Kernel Mode Setting (KMS)¶

Drivers must initialize the mode setting core by calling drmm_mode_config_init() on the DRM device. The function initializes the struct drm_device mode_config field and never fails. Once done, mode configuration must be setup by initializing the following fields.

int min_width, min_height; int max_width, max_height; Minimum and maximum width and height of the frame buffers in pixel units.
struct drm_mode_config_funcs *funcs; Mode setting functions.

Overview¶

The basic object structure KMS presents to userspace is fairly simple. Framebuffers (represented by struct drm_framebuffer, see Frame Buffer Abstraction) feed into planes. Planes are represented by struct drm_plane, see Plane Abstraction for more details. One or more (or even no) planes feed their pixel data into a CRTC (represented by struct drm_crtc, see CRTC Abstraction) for blending. The precise blending step is explained in more detail in Plane Composition Properties and related chapters.

For the output routing the first step is encoders (represented by struct drm_encoder, see Encoder Abstraction). Those are really just internal artifacts of the helper libraries used to implement KMS drivers. Besides that they make it unecessarily more complicated for userspace to figure out which connections between a CRTC and a connector are possible, and what kind of cloning is supported, they serve no purpose in the userspace API. Unfortunately encoders have been exposed to userspace, hence can’t remove them at this point. Futhermore the exposed restrictions are often wrongly set by drivers, and in many cases not powerful enough to express the real restrictions. A CRTC can be connected to multiple encoders, and for an active CRTC there must be at least one encoder.

The final, and real, endpoint in the display chain is the connector (represented by struct drm_connector, see Connector Abstraction). Connectors can have different possible encoders, but the kernel driver selects which encoder to use for each connector. The use case is DVI, which could switch between an analog and a digital encoder. Encoders can also drive multiple different connectors. There is exactly one active connector for every active encoder.

Internally the output pipeline is a bit more complex and matches today’s hardware more closely:

Internally two additional helper objects come into play. First, to be able to share code for encoders (sometimes on the same SoC, sometimes off-chip) one or more Bridges (represented by struct drm_bridge) can be linked to an encoder. This link is static and cannot be changed, which means the cross-bar (if there is any) needs to be mapped between the CRTC and any encoders. Often for drivers with bridges there’s no code left at the encoder level. Atomic drivers can leave out all the encoder callbacks to essentially only leave a dummy routing object behind, which is needed for backwards compatibility since encoders are exposed to userspace.

The second object is for panels, represented by struct drm_panel, see Panel Helper Reference. Panels do not have a fixed binding point, but are generally linked to the driver private structure that embeds struct drm_connector.

Note that currently the bridge chaining and interactions with connectors and panels are still in-flux and not really fully sorted out yet.

KMS Core Structures and Functions¶

struct drm_mode_config_funcs¶: basic driver provided mode setting functions

Definition

struct drm_mode_config_funcs {
  struct drm_framebuffer *(*fb_create)(struct drm_device *dev,struct drm_file *file_priv, const struct drm_mode_fb_cmd2 *mode_cmd);
  const struct drm_format_info *(*get_format_info)(const struct drm_mode_fb_cmd2 *mode_cmd);
  void (*output_poll_changed)(struct drm_device *dev);
  enum drm_mode_status (*mode_valid)(struct drm_device *dev, const struct drm_display_mode *mode);
  int (*atomic_check)(struct drm_device *dev, struct drm_atomic_state *state);
  int (*atomic_commit)(struct drm_device *dev,struct drm_atomic_state *state, bool nonblock);
  struct drm_atomic_state *(*atomic_state_alloc)(struct drm_device *dev);
  void (*atomic_state_clear)(struct drm_atomic_state *state);
  void (*atomic_state_free)(struct drm_atomic_state *state);
};

Members

fb_create

Create a new framebuffer object. The core does basic checks on the requested metadata, but most of that is left to the driver. See struct drm_mode_fb_cmd2 for details.

To validate the pixel format and modifier drivers can use drm_any_plane_has_format() to make sure at least one plane supports the requested values. Note that the driver must first determine the actual modifier used if the request doesn’t have it specified, ie. when (mode_cmd->flags & DRM_MODE_FB_MODIFIERS) == 0.

IMPORTANT: These implied modifiers for legacy userspace must be stored in struct drm_framebuffer, including all relevant metadata like drm_framebuffer.pitches and drm_framebuffer.offsets if the modifier enables additional planes beyond the fourcc pixel format code. This is required by the GETFB2 ioctl.

If the parameters are deemed valid and the backing storage objects in the underlying memory manager all exist, then the driver allocates a new drm_framebuffer structure, subclassed to contain driver-specific information (like the internal native buffer object references). It also needs to fill out all relevant metadata, which should be done by calling drm_helper_mode_fill_fb_struct().

The initialization is finalized by calling drm_framebuffer_init(), which registers the framebuffer and makes it accessible to other threads.

RETURNS:

A new framebuffer with an initial reference count of 1 or a negative error code encoded with ERR_PTR().

get_format_info

Allows a driver to return custom format information for special fb layouts (eg. ones with auxiliary compression control planes).

RETURNS:

The format information specific to the given fb metadata, or NULL if none is found.

output_poll_changed

Callback used by helpers to inform the driver of output configuration changes.

Drivers implementing fbdev emulation use drm_kms_helper_hotplug_event() to call this hook to inform the fbdev helper of output changes.

This hook is deprecated, drivers should instead use drm_fbdev_generic_setup() which takes care of any necessary hotplug event forwarding already without further involvement by the driver.

mode_valid

Device specific validation of display modes. Can be used to reject modes that can never be supported. Only device wide constraints can be checked here. crtc/encoder/bridge/connector specific constraints should be checked in the .mode_valid() hook for each specific object.

atomic_check

This is the only hook to validate an atomic modeset update. This function must reject any modeset and state changes which the hardware or driver doesn’t support. This includes but is of course not limited to:

Checking that the modes, framebuffers, scaling and placement requirements and so on are within the limits of the hardware.

Checking that any hidden shared resources are not oversubscribed. This can be shared PLLs, shared lanes, overall memory bandwidth, display fifo space (where shared between planes or maybe even CRTCs).

Checking that virtualized resources exported to userspace are not oversubscribed. For various reasons it can make sense to expose more planes, crtcs or encoders than which are physically there. One example is dual-pipe operations (which generally should be hidden from userspace if when lockstepped in hardware, exposed otherwise), where a plane might need 1 hardware plane (if it’s just on one pipe), 2 hardware planes (when it spans both pipes) or maybe even shared a hardware plane with a 2nd plane (if there’s a compatible plane requested on the area handled by the other pipe).

Check that any transitional state is possible and that if requested, the update can indeed be done in the vblank period without temporarily disabling some functions.

Check any other constraints the driver or hardware might have.

This callback also needs to correctly fill out the drm_crtc_state in this update to make sure that drm_atomic_crtc_needs_modeset() reflects the nature of the possible update and returns true if and only if the update cannot be applied without tearing within one vblank on that CRTC. The core uses that information to reject updates which require a full modeset (i.e. blanking the screen, or at least pausing updates for a substantial amount of time) if userspace has disallowed that in its request.

The driver also does not need to repeat basic input validation like done for the corresponding legacy entry points. The core does that before calling this hook.

See the documentation of atomic_commit for an exhaustive list of error conditions which don’t have to be checked at the in this callback.

See the documentation for struct drm_atomic_state for how exactly an atomic modeset update is described.

Drivers using the atomic helpers can implement this hook using drm_atomic_helper_check(), or one of the exported sub-functions of it.

RETURNS:

0 on success or one of the below negative error codes:

-EINVAL, if any of the above constraints are violated.

-EDEADLK, when returned from an attempt to acquire an additional drm_modeset_lock through drm_modeset_lock().

-ENOMEM, if allocating additional state sub-structures failed due to lack of memory.

-EINTR, -EAGAIN or -ERESTARTSYS, if the IOCTL should be restarted. This can either be due to a pending signal, or because the driver needs to completely bail out to recover from an exceptional situation like a GPU hang. From a userspace point all errors are treated equally.

atomic_commit

This is the only hook to commit an atomic modeset update. The core guarantees that atomic_check has been called successfully before calling this function, and that nothing has been changed in the interim.

See the documentation for struct drm_atomic_state for how exactly an atomic modeset update is described.

Drivers using the atomic helpers can implement this hook using drm_atomic_helper_commit(), or one of the exported sub-functions of it.

Nonblocking commits (as indicated with the nonblock parameter) must do any preparatory work which might result in an unsuccessful commit in the context of this callback. The only exceptions are hardware errors resulting in -EIO. But even in that case the driver must ensure that the display pipe is at least running, to avoid compositors crashing when pageflips don’t work. Anything else, specifically committing the update to the hardware, should be done without blocking the caller. For updates which do not require a modeset this must be guaranteed.

The driver must wait for any pending rendering to the new framebuffers to complete before executing the flip. It should also wait for any pending rendering from other drivers if the underlying buffer is a shared dma-buf. Nonblocking commits must not wait for rendering in the context of this callback.

An application can request to be notified when the atomic commit has completed. These events are per-CRTC and can be distinguished by the CRTC index supplied in drm_event to userspace.

The drm core will supply a struct drm_event in each CRTC’s drm_crtc_state.event. See the documentation for drm_crtc_state.event for more details about the precise semantics of this event.

NOTE:

Drivers are not allowed to shut down any display pipe successfully enabled through an atomic commit on their own. Doing so can result in compositors crashing if a page flip is suddenly rejected because the pipe is off.

RETURNS:

0 on success or one of the below negative error codes:

-EBUSY, if a nonblocking updated is requested and there is an earlier updated pending. Drivers are allowed to support a queue of outstanding updates, but currently no driver supports that. Note that drivers must wait for preceding updates to complete if a synchronous update is requested, they are not allowed to fail the commit in that case.

-ENOMEM, if the driver failed to allocate memory. Specifically this can happen when trying to pin framebuffers, which must only be done when committing the state.

-ENOSPC, as a refinement of the more generic -ENOMEM to indicate that the driver has run out of vram, iommu space or similar GPU address space needed for framebuffer.

-EIO, if the hardware completely died.

-EINTR, -EAGAIN or -ERESTARTSYS, if the IOCTL should be restarted. This can either be due to a pending signal, or because the driver needs to completely bail out to recover from an exceptional situation like a GPU hang. From a userspace point of view all errors are treated equally.

This list is exhaustive. Specifically this hook is not allowed to return -EINVAL (any invalid requests should be caught in atomic_check) or -EDEADLK (this function must not acquire additional modeset locks).

atomic_state_alloc

This optional hook can be used by drivers that want to subclass struct drm_atomic_state to be able to track their own driver-private global state easily. If this hook is implemented, drivers must also implement atomic_state_clear and atomic_state_free.

Subclassing of drm_atomic_state is deprecated in favour of using drm_private_state and drm_private_obj.

RETURNS:

A new drm_atomic_state on success or NULL on failure.

atomic_state_clear

This hook must clear any driver private state duplicated into the passed-in drm_atomic_state. This hook is called when the caller encountered a drm_modeset_lock deadlock and needs to drop all already acquired locks as part of the deadlock avoidance dance implemented in drm_modeset_backoff().

Any duplicated state must be invalidated since a concurrent atomic update might change it, and the drm atomic interfaces always apply updates as relative changes to the current state.

Drivers that implement this must call drm_atomic_state_default_clear() to clear common state.

Subclassing of drm_atomic_state is deprecated in favour of using drm_private_state and drm_private_obj.

atomic_state_free

This hook needs driver private resources and the drm_atomic_state itself. Note that the core first calls drm_atomic_state_clear() to avoid code duplicate between the clear and free hooks.

Drivers that implement this must call drm_atomic_state_default_release() to release common resources.

Subclassing of drm_atomic_state is deprecated in favour of using drm_private_state and drm_private_obj.

Description

Some global (i.e. not per-CRTC, connector, etc) mode setting functions that involve drivers.

struct drm_mode_config¶: Mode configuration control structure

Definition

struct drm_mode_config {
  struct mutex mutex;
  struct drm_modeset_lock connection_mutex;
  struct drm_modeset_acquire_ctx *acquire_ctx;
  struct mutex idr_mutex;
  struct idr object_idr;
  struct idr tile_idr;
  struct mutex fb_lock;
  int num_fb;
  struct list_head fb_list;
  spinlock_t connector_list_lock;
  int num_connector;
  struct ida connector_ida;
  struct list_head connector_list;
  struct llist_head connector_free_list;
  struct work_struct connector_free_work;
  int num_encoder;
  struct list_head encoder_list;
  int num_total_plane;
  struct list_head plane_list;
  int num_crtc;
  struct list_head crtc_list;
  struct list_head property_list;
  struct list_head privobj_list;
  int min_width, min_height;
  int max_width, max_height;
  const struct drm_mode_config_funcs *funcs;
  resource_size_t fb_base;
  bool poll_enabled;
  bool poll_running;
  bool delayed_event;
  struct delayed_work output_poll_work;
  struct mutex blob_lock;
  struct list_head property_blob_list;
  struct drm_property *edid_property;
  struct drm_property *dpms_property;
  struct drm_property *path_property;
  struct drm_property *tile_property;
  struct drm_property *link_status_property;
  struct drm_property *plane_type_property;
  struct drm_property *prop_src_x;
  struct drm_property *prop_src_y;
  struct drm_property *prop_src_w;
  struct drm_property *prop_src_h;
  struct drm_property *prop_crtc_x;
  struct drm_property *prop_crtc_y;
  struct drm_property *prop_crtc_w;
  struct drm_property *prop_crtc_h;
  struct drm_property *prop_fb_id;
  struct drm_property *prop_in_fence_fd;
  struct drm_property *prop_out_fence_ptr;
  struct drm_property *prop_crtc_id;
  struct drm_property *prop_fb_damage_clips;
  struct drm_property *prop_active;
  struct drm_property *prop_mode_id;
  struct drm_property *prop_vrr_enabled;
  struct drm_property *dvi_i_subconnector_property;
  struct drm_property *dvi_i_select_subconnector_property;
  struct drm_property *dp_subconnector_property;
  struct drm_property *tv_subconnector_property;
  struct drm_property *tv_select_subconnector_property;
  struct drm_property *tv_mode_property;
  struct drm_property *tv_left_margin_property;
  struct drm_property *tv_right_margin_property;
  struct drm_property *tv_top_margin_property;
  struct drm_property *tv_bottom_margin_property;
  struct drm_property *tv_brightness_property;
  struct drm_property *tv_contrast_property;
  struct drm_property *tv_flicker_reduction_property;
  struct drm_property *tv_overscan_property;
  struct drm_property *tv_saturation_property;
  struct drm_property *tv_hue_property;
  struct drm_property *scaling_mode_property;
  struct drm_property *aspect_ratio_property;
  struct drm_property *content_type_property;
  struct drm_property *degamma_lut_property;
  struct drm_property *degamma_lut_size_property;
  struct drm_property *ctm_property;
  struct drm_property *gamma_lut_property;
  struct drm_property *gamma_lut_size_property;
  struct drm_property *suggested_x_property;
  struct drm_property *suggested_y_property;
  struct drm_property *non_desktop_property;
  struct drm_property *panel_orientation_property;
  struct drm_property *writeback_fb_id_property;
  struct drm_property *writeback_pixel_formats_property;
  struct drm_property *writeback_out_fence_ptr_property;
  struct drm_property *hdr_output_metadata_property;
  struct drm_property *content_protection_property;
  struct drm_property *hdcp_content_type_property;
  uint32_t preferred_depth, prefer_shadow;
  bool prefer_shadow_fbdev;
  bool quirk_addfb_prefer_xbgr_30bpp;
  bool quirk_addfb_prefer_host_byte_order;
  bool async_page_flip;
  bool fb_modifiers_not_supported;
  bool normalize_zpos;
  struct drm_property *modifiers_property;
  uint32_t cursor_width, cursor_height;
  struct drm_atomic_state *suspend_state;
  const struct drm_mode_config_helper_funcs *helper_private;
};

Members

mutex

This is the big scary modeset BKL which protects everything that isn’t protect otherwise. Scope is unclear and fuzzy, try to remove anything from under its protection and move it into more well-scoped locks.

The one important thing this protects is the use of acquire_ctx.

connection_mutex

This protects connector state and the connector to encoder to CRTC routing chain.

For atomic drivers specifically this protects drm_connector.state.

acquire_ctx

Global implicit acquire context used by atomic drivers for legacy IOCTLs. Deprecated, since implicit locking contexts make it impossible to use driver-private struct drm_modeset_lock. Users of this must hold mutex.

idr_mutex

Mutex for KMS ID allocation and management. Protects both object_idr and tile_idr.

object_idr

Main KMS ID tracking object. Use this idr for all IDs, fb, crtc, connector, modes - just makes life easier to have only one.

tile_idr

Use this idr for allocating new IDs for tiled sinks like use in some high-res DP MST screens.

fb_lock

Mutex to protect fb the global fb_list and num_fb.

num_fb

Number of entries on fb_list.

fb_list

List of all struct drm_framebuffer.

connector_list_lock

Protects num_connector and connector_list and connector_free_list.

num_connector

Number of connectors on this device. Protected by connector_list_lock.

connector_ida

ID allocator for connector indices.

connector_list

List of connector objects linked with drm_connector.head. Protected by connector_list_lock. Only use drm_for_each_connector_iter() and struct drm_connector_list_iter to walk this list.

connector_free_list

List of connector objects linked with drm_connector.free_head. Protected by connector_list_lock. Used by drm_for_each_connector_iter() and struct drm_connector_list_iter to savely free connectors using connector_free_work.

connector_free_work

Work to clean up connector_free_list.

num_encoder

Number of encoders on this device. This is invariant over the lifetime of a device and hence doesn’t need any locks.

encoder_list

List of encoder objects linked with drm_encoder.head. This is invariant over the lifetime of a device and hence doesn’t need any locks.

num_total_plane

Number of universal (i.e. with primary/curso) planes on this device. This is invariant over the lifetime of a device and hence doesn’t need any locks.

plane_list

List of plane objects linked with drm_plane.head. This is invariant over the lifetime of a device and hence doesn’t need any locks.

num_crtc

Number of CRTCs on this device linked with drm_crtc.head. This is invariant over the lifetime of a device and hence doesn’t need any locks.

crtc_list

List of CRTC objects linked with drm_crtc.head. This is invariant over the lifetime of a device and hence doesn’t need any locks.

property_list

List of property type objects linked with drm_property.head. This is invariant over the lifetime of a device and hence doesn’t need any locks.

privobj_list

List of private objects linked with drm_private_obj.head. This is invariant over the lifetime of a device and hence doesn’t need any locks.

min_width

minimum fb pixel width on this device

min_height

minimum fb pixel height on this device

max_width

maximum fb pixel width on this device

max_height

maximum fb pixel height on this device

funcs

core driver provided mode setting functions

fb_base

base address of the framebuffer

poll_enabled

track polling support for this device

poll_running

track polling status for this device

delayed_event

track delayed poll uevent deliver for this device

output_poll_work

delayed work for polling in process context

blob_lock

Mutex for blob property allocation and management, protects property_blob_list and drm_file.blobs.

property_blob_list

List of all the blob property objects linked with drm_property_blob.head. Protected by blob_lock.

edid_property

Default connector property to hold the EDID of the currently connected sink, if any.

dpms_property

Default connector property to control the connector’s DPMS state.

path_property

Default connector property to hold the DP MST path for the port.

tile_property

Default connector property to store the tile position of a tiled screen, for sinks which need to be driven with multiple CRTCs.

link_status_property

Default connector property for link status of a connector

plane_type_property

Default plane property to differentiate CURSOR, PRIMARY and OVERLAY legacy uses of planes.

prop_src_x

Default atomic plane property for the plane source position in the connected drm_framebuffer.

prop_src_y

Default atomic plane property for the plane source position in the connected drm_framebuffer.

prop_src_w

Default atomic plane property for the plane source position in the connected drm_framebuffer.

prop_src_h

Default atomic plane property for the plane source position in the connected drm_framebuffer.

prop_crtc_x

Default atomic plane property for the plane destination position in the drm_crtc is being shown on.

prop_crtc_y

Default atomic plane property for the plane destination position in the drm_crtc is being shown on.

prop_crtc_w

Default atomic plane property for the plane destination position in the drm_crtc is being shown on.

prop_crtc_h

Default atomic plane property for the plane destination position in the drm_crtc is being shown on.

prop_fb_id

Default atomic plane property to specify the drm_framebuffer.

prop_in_fence_fd

Sync File fd representing the incoming fences for a Plane.

prop_out_fence_ptr

Sync File fd pointer representing the outgoing fences for a CRTC. Userspace should provide a pointer to a value of type s32, and then cast that pointer to u64.

prop_crtc_id

Default atomic plane property to specify the drm_crtc.

prop_fb_damage_clips

Optional plane property to mark damaged regions on the plane in framebuffer coordinates of the framebuffer attached to the plane.

The layout of blob data is simply an array of drm_mode_rect. Unlike plane src coordinates, damage clips are not in 16.16 fixed point.

prop_active

Default atomic CRTC property to control the active state, which is the simplified implementation for DPMS in atomic drivers.

prop_mode_id

Default atomic CRTC property to set the mode for a CRTC. A 0 mode implies that the CRTC is entirely disabled - all connectors must be of and active must be set to disabled, too.

prop_vrr_enabled

Default atomic CRTC property to indicate whether variable refresh rate should be enabled on the CRTC.

dvi_i_subconnector_property

Optional DVI-I property to differentiate between analog or digital mode.

dvi_i_select_subconnector_property

Optional DVI-I property to select between analog or digital mode.

dp_subconnector_property

Optional DP property to differentiate between different DP downstream port types.

tv_subconnector_property

Optional TV property to differentiate between different TV connector types.

tv_select_subconnector_property

Optional TV property to select between different TV connector types.

tv_mode_property

Optional TV property to select the output TV mode.

tv_left_margin_property

Optional TV property to set the left margin (expressed in pixels).

tv_right_margin_property

Optional TV property to set the right margin (expressed in pixels).

tv_top_margin_property

Optional TV property to set the right margin (expressed in pixels).

tv_bottom_margin_property

Optional TV property to set the right margin (expressed in pixels).

tv_brightness_property

Optional TV property to set the brightness.

tv_contrast_property

Optional TV property to set the contrast.

tv_flicker_reduction_property

Optional TV property to control the flicker reduction mode.

tv_overscan_property

Optional TV property to control the overscan setting.

tv_saturation_property

Optional TV property to set the saturation.

tv_hue_property

Optional TV property to set the hue.

scaling_mode_property

Optional connector property to control the upscaling, mostly used for built-in panels.

aspect_ratio_property

Optional connector property to control the HDMI infoframe aspect ratio setting.

content_type_property

Optional connector property to control the HDMI infoframe content type setting.

degamma_lut_property

Optional CRTC property to set the LUT used to convert the framebuffer’s colors to linear gamma.

degamma_lut_size_property

Optional CRTC property for the size of the degamma LUT as supported by the driver (read-only).

ctm_property

Optional CRTC property to set the matrix used to convert colors after the lookup in the degamma LUT.

gamma_lut_property

Optional CRTC property to set the LUT used to convert the colors, after the CTM matrix, to the gamma space of the connected screen.

gamma_lut_size_property

Optional CRTC property for the size of the gamma LUT as supported by the driver (read-only).

suggested_x_property

Optional connector property with a hint for the position of the output on the host’s screen.

suggested_y_property

Optional connector property with a hint for the position of the output on the host’s screen.

non_desktop_property

Optional connector property with a hint that device isn’t a standard display, and the console/desktop, should not be displayed on it.

panel_orientation_property

Optional connector property indicating how the lcd-panel is mounted inside the casing (e.g. normal or upside-down).

writeback_fb_id_property

Property for writeback connectors, storing the ID of the output framebuffer. See also: drm_writeback_connector_init()

writeback_pixel_formats_property

Property for writeback connectors, storing an array of the supported pixel formats for the writeback engine (read-only). See also: drm_writeback_connector_init()

writeback_out_fence_ptr_property

Property for writeback connectors, fd pointer representing the outgoing fences for a writeback connector. Userspace should provide a pointer to a value of type s32, and then cast that pointer to u64. See also: drm_writeback_connector_init()

hdr_output_metadata_property

Connector property containing hdr metatada. This will be provided by userspace compositors based on HDR content

content_protection_property

DRM ENUM property for content protection. See drm_connector_attach_content_protection_property().

hdcp_content_type_property

DRM ENUM property for type of Protected Content.

preferred_depth

preferred RBG pixel depth, used by fb helpers

prefer_shadow

hint to userspace to prefer shadow-fb rendering

prefer_shadow_fbdev

Hint to framebuffer emulation to prefer shadow-fb rendering.

quirk_addfb_prefer_xbgr_30bpp

Special hack for legacy ADDFB to keep nouveau userspace happy. Should only ever be set by the nouveau kernel driver.

quirk_addfb_prefer_host_byte_order

When set to true drm_mode_addfb() will pick host byte order pixel_format when calling drm_mode_addfb2(). This is how drm_mode_addfb() should have worked from day one. It didn’t though, so we ended up with quirks in both kernel and userspace drivers to deal with the broken behavior. Simply fixing drm_mode_addfb() unconditionally would break these drivers, so add a quirk bit here to allow drivers opt-in.

async_page_flip

Does this device support async flips on the primary plane?

fb_modifiers_not_supported

When this flag is set, the DRM device will not expose modifier support to userspace. This is only used by legacy drivers that infer the buffer layout through heuristics without using modifiers. New drivers shall not set fhis flag.

normalize_zpos

If true the drm core will call drm_atomic_normalize_zpos() as part of atomic mode checking from drm_atomic_helper_check()

modifiers_property

Plane property to list support modifier/format combination.

cursor_width

hint to userspace for max cursor width

cursor_height

hint to userspace for max cursor height

suspend_state

Atomic state when suspended. Set by drm_mode_config_helper_suspend() and cleared by drm_mode_config_helper_resume().

helper_private

mid-layer private data

Description

Core mode resource tracking structure. All CRTC, encoders, and connectors enumerated by the driver are added here, as are global properties. Some global restrictions are also here, e.g. dimension restrictions.

Framebuffer sizes refer to the virtual screen that can be displayed by the CRTC. This can be different from the physical resolution programmed. The minimum width and height, stored in min_width and min_height, describe the smallest size of the framebuffer. It correlates to the minimum programmable resolution. The maximum width, stored in max_width, is typically limited by the maximum pitch between two adjacent scanlines. The maximum height, stored in max_height, is usually only limited by the amount of addressable video memory. For hardware that has no real maximum, drivers should pick a reasonable default.

See also DRM_SHADOW_PLANE_MAX_WIDTH and DRM_SHADOW_PLANE_MAX_HEIGHT.

int drm_mode_config_init(struct drm_device *dev)¶: DRM mode_configuration structure initialization

Parameters

struct drm_device *dev: DRM device

Description

This is the unmanaged version of drmm_mode_config_init() for drivers which still explicitly call drm_mode_config_cleanup().

FIXME: This function is deprecated and drivers should be converted over to drmm_mode_config_init().

void drm_mode_config_reset(struct drm_device *dev)¶: call ->reset callbacks

Parameters

struct drm_device *dev: drm device

Description

This functions calls all the crtc’s, encoder’s and connector’s ->reset callback. Drivers can use this in e.g. their driver load or resume code to reset hardware and software state.

int drmm_mode_config_init(struct drm_device *dev)¶: managed DRM mode_configuration structure initialization

Parameters

struct drm_device *dev: DRM device

Description

Initialize dev’s mode_config structure, used for tracking the graphics configuration of dev.

Since this initializes the modeset locks, no locking is possible. Which is no problem, since this should happen single threaded at init time. It is the driver’s problem to ensure this guarantee.

Cleanup is automatically handled through registering drm_mode_config_cleanup with drmm_add_action().

Return

0 on success, negative error value on failure.

void drm_mode_config_cleanup(struct drm_device *dev)¶: free up DRM mode_config info

Parameters

struct drm_device *dev: DRM device

Description

Free up all the connectors and CRTCs associated with this DRM device, then free up the framebuffers and associated buffer objects.

Note that since this /should/ happen single-threaded at driver/device teardown time, no locking is required. It’s the driver’s job to ensure that this guarantee actually holds true.

FIXME: With the managed drmm_mode_config_init() it is no longer necessary for drivers to explicitly call this function.

Modeset Base Object Abstraction¶

The base structure for all KMS objects is struct drm_mode_object. One of the base services it provides is tracking properties, which are especially important for the atomic IOCTL (see Atomic Mode Setting). The somewhat surprising part here is that properties are not directly instantiated on each object, but free-standing mode objects themselves, represented by struct drm_property, which only specify the type and value range of a property. Any given property can be attached multiple times to different objects using drm_object_attach_property().

struct drm_mode_object¶: base structure for modeset objects

Definition

struct drm_mode_object {
  uint32_t id;
  uint32_t type;
  struct drm_object_properties *properties;
  struct kref refcount;
  void (*free_cb)(struct kref *kref);
};

Members

id: userspace visible identifier
type: type of the object, one of DRM_MODE_OBJECT_*
properties: properties attached to this object, including values
refcount: reference count for objects which with dynamic lifetime
free_cb: free function callback, only set for objects with dynamic lifetime

Description

Base structure for modeset objects visible to userspace. Objects can be looked up using drm_mode_object_find(). Besides basic uapi interface properties like id and type it provides two services:

It tracks attached properties and their values. This is used by drm_crtc, drm_plane and drm_connector. Properties are attached by calling drm_object_attach_property() before the object is visible to userspace.
For objects with dynamic lifetimes (as indicated by a non-NULL free_cb) it provides reference counting through drm_mode_object_get() and drm_mode_object_put(). This is used by drm_framebuffer, drm_connector and drm_property_blob. These objects provide specialized reference counting wrappers.

struct drm_object_properties¶: property tracking for drm_mode_object

Definition

struct drm_object_properties {
  int count;
  struct drm_property *properties[DRM_OBJECT_MAX_PROPERTY];
  uint64_t values[DRM_OBJECT_MAX_PROPERTY];
};

Members

count

number of valid properties, must be less than or equal to DRM_OBJECT_MAX_PROPERTY.

properties

Array of pointers to drm_property.

NOTE: if we ever start dynamically destroying properties (ie. not at drm_mode_config_cleanup() time), then we’d have to do a better job of detaching property from mode objects to avoid dangling property pointers:

values

Array to store the property values, matching properties. Do not read/write values directly, but use drm_object_property_get_value() and drm_object_property_set_value().

Note that atomic drivers do not store mutable properties in this array, but only the decoded values in the corresponding state structure. The decoding is done using the drm_crtc.atomic_get_property and drm_crtc.atomic_set_property hooks for struct drm_crtc. For struct drm_plane the hooks are drm_plane_funcs.atomic_get_property and drm_plane_funcs.atomic_set_property. And for struct drm_connector the hooks are drm_connector_funcs.atomic_get_property and drm_connector_funcs.atomic_set_property .

Hence atomic drivers should not use drm_object_property_set_value() and drm_object_property_get_value() on mutable objects, i.e. those without the DRM_MODE_PROP_IMMUTABLE flag set.

For atomic drivers the default value of properties is stored in this array, so drm_object_property_get_default_value can be used to retrieve it.

struct drm_mode_object *drm_mode_object_find(struct drm_device *dev, struct drm_file *file_priv, uint32_t id, uint32_t type)¶: look up a drm object with static lifetime

Parameters

struct drm_device *dev: drm device
struct drm_file *file_priv: drm file
uint32_t id: id of the mode object
uint32_t type: type of the mode object

Description

This function is used to look up a modeset object. It will acquire a reference for reference counted objects. This reference must be dropped again by callind drm_mode_object_put().

void drm_mode_object_put(struct drm_mode_object *obj)¶: release a mode object reference

Parameters

struct drm_mode_object *obj: DRM mode object

Description

This function decrements the object’s refcount if it is a refcounted modeset object. It is a no-op on any other object. This is used to drop references acquired with drm_mode_object_get().

void drm_mode_object_get(struct drm_mode_object *obj)¶: acquire a mode object reference

Parameters

struct drm_mode_object *obj: DRM mode object

Description

This function increments the object’s refcount if it is a refcounted modeset object. It is a no-op on any other object. References should be dropped again by calling drm_mode_object_put().

void drm_object_attach_property(struct drm_mode_object *obj, struct drm_property *property, uint64_t init_val)¶: attach a property to a modeset object

Parameters

struct drm_mode_object *obj: drm modeset object
struct drm_property *property: property to attach
uint64_t init_val: initial value of the property

Description

This attaches the given property to the modeset object with the given initial value. Currently this function cannot fail since the properties are stored in a statically sized array.

Note that all properties must be attached before the object itself is registered and accessible from userspace.

int drm_object_property_set_value(struct drm_mode_object *obj, struct drm_property *property, uint64_t val)¶: set the value of a property

Parameters

struct drm_mode_object *obj: drm mode object to set property value for
struct drm_property *property: property to set
uint64_t val: value the property should be set to

Description

This function sets a given property on a given object. This function only changes the software state of the property, it does not call into the driver’s ->set_property callback.

Note that atomic drivers should not have any need to call this, the core will ensure consistency of values reported back to userspace through the appropriate ->atomic_get_property callback. Only legacy drivers should call this function to update the tracked value (after clamping and other restrictions have been applied).

Return

Zero on success, error code on failure.

int drm_object_property_get_value(struct drm_mode_object *obj, struct drm_property *property, uint64_t *val)¶: retrieve the value of a property

Parameters

struct drm_mode_object *obj: drm mode object to get property value from
struct drm_property *property: property to retrieve
uint64_t *val: storage for the property value

Description

This function retrieves the softare state of the given property for the given property. Since there is no driver callback to retrieve the current property value this might be out of sync with the hardware, depending upon the driver and property.

Atomic drivers should never call this function directly, the core will read out property values through the various ->atomic_get_property callbacks.

Return

Zero on success, error code on failure.

int drm_object_property_get_default_value(struct drm_mode_object *obj, struct drm_property *property, uint64_t *val)¶: retrieve the default value of a property when in atomic mode.

Parameters

struct drm_mode_object *obj: drm mode object to get property value from
struct drm_property *property: property to retrieve
uint64_t *val: storage for the property value

Description

This function retrieves the default state of the given property as passed in to drm_object_attach_property

Only atomic drivers should call this function directly, as for non-atomic drivers it will return the current value.

Return

Zero on success, error code on failure.

Atomic Mode Setting¶

Atomic provides transactional modeset (including planes) updates, but a bit differently from the usual transactional approach of try-commit and rollback:

Firstly, no hardware changes are allowed when the commit would fail. This allows us to implement the DRM_MODE_ATOMIC_TEST_ONLY mode, which allows userspace to explore whether certain configurations would work or not.
This would still allow setting and rollback of just the software state, simplifying conversion of existing drivers. But auditing drivers for correctness of the atomic_check code becomes really hard with that: Rolling back changes in data structures all over the place is hard to get right.
Lastly, for backwards compatibility and to support all use-cases, atomic updates need to be incremental and be able to execute in parallel. Hardware doesn’t always allow it, but where possible plane updates on different CRTCs should not interfere, and not get stalled due to output routing changing on different CRTCs.

Taken all together there’s two consequences for the atomic design:

The overall state is split up into per-object state structures: struct drm_plane_state for planes, struct drm_crtc_state for CRTCs and struct drm_connector_state for connectors. These are the only objects with userspace-visible and settable state. For internal state drivers can subclass these structures through embeddeding, or add entirely new state structures for their globally shared hardware functions, see struct drm_private_state.
An atomic update is assembled and validated as an entirely free-standing pile of structures within the drm_atomic_state container. Driver private state structures are also tracked in the same structure; see the next chapter. Only when a state is committed is it applied to the driver and modeset objects. This way rolling back an update boils down to releasing memory and unreferencing objects like framebuffers.

Locking of atomic state structures is internally using struct drm_modeset_lock. As a general rule the locking shouldn’t be exposed to drivers, instead the right locks should be automatically acquired by any function that duplicates or peeks into a state, like e.g. drm_atomic_get_crtc_state(). Locking only protects the software data structure, ordering of committing state changes to hardware is sequenced using struct drm_crtc_commit.

Read on in this chapter, and also in Atomic Modeset Helper Functions Reference for more detailed coverage of specific topics.

Handling Driver Private State¶

Very often the DRM objects exposed to userspace in the atomic modeset api (drm_connector, drm_crtc and drm_plane) do not map neatly to the underlying hardware. Especially for any kind of shared resources (e.g. shared clocks, scaler units, bandwidth and fifo limits shared among a group of planes or CRTCs, and so on) it makes sense to model these as independent objects. Drivers then need to do similar state tracking and commit ordering for such private (since not exposed to userspace) objects as the atomic core and helpers already provide for connectors, planes and CRTCs.

To make this easier on drivers the atomic core provides some support to track driver private state objects using struct drm_private_obj, with the associated state struct drm_private_state.

Similar to userspace-exposed objects, private state structures can be acquired by calling drm_atomic_get_private_obj_state(). This also takes care of locking, hence drivers should not have a need to call drm_modeset_lock() directly. Sequence of the actual hardware state commit is not handled, drivers might need to keep track of struct drm_crtc_commit within subclassed structure of drm_private_state as necessary, e.g. similar to drm_plane_state.commit. See also drm_atomic_state.fake_commit.

All private state structures contained in a drm_atomic_state update can be iterated using for_each_oldnew_private_obj_in_state(), for_each_new_private_obj_in_state() and for_each_old_private_obj_in_state(). Drivers are recommended to wrap these for each type of driver private state object they have, filtering on drm_private_obj.funcs using for_each_if(), at least if they want to iterate over all objects of a given type.

An earlier way to handle driver private state was by subclassing struct drm_atomic_state. But since that encourages non-standard ways to implement the check/commit split atomic requires (by using e.g. “check and rollback or commit instead” of “duplicate state, check, then either commit or release duplicated state) it is deprecated in favour of using drm_private_state.

Atomic Mode Setting Function Reference¶

struct drm_crtc_commit¶: track modeset commits on a CRTC

Definition

struct drm_crtc_commit {
  struct drm_crtc *crtc;
  struct kref ref;
  struct completion flip_done;
  struct completion hw_done;
  struct completion cleanup_done;
  struct list_head commit_entry;
  struct drm_pending_vblank_event *event;
  bool abort_completion;
};

Members

crtc

DRM CRTC for this commit.

ref

Reference count for this structure. Needed to allow blocking on completions without the risk of the completion disappearing meanwhile.

flip_done

Will be signaled when the hardware has flipped to the new set of buffers. Signals at the same time as when the drm event for this commit is sent to userspace, or when an out-fence is singalled. Note that for most hardware, in most cases this happens after hw_done is signalled.

Completion of this stage is signalled implicitly by calling drm_crtc_send_vblank_event() on drm_crtc_state.event.

hw_done

Will be signalled when all hw register changes for this commit have been written out. Especially when disabling a pipe this can be much later than flip_done, since that can signal already when the screen goes black, whereas to fully shut down a pipe more register I/O is required.

Note that this does not need to include separately reference-counted resources like backing storage buffer pinning, or runtime pm management.

Drivers should call drm_atomic_helper_commit_hw_done() to signal completion of this stage.

cleanup_done

Will be signalled after old buffers have been cleaned up by calling drm_atomic_helper_cleanup_planes(). Since this can only happen after a vblank wait completed it might be a bit later. This completion is useful to throttle updates and avoid hardware updates getting ahead of the buffer cleanup too much.

Drivers should call drm_atomic_helper_commit_cleanup_done() to signal completion of this stage.

commit_entry

Entry on the per-CRTC drm_crtc.commit_list. Protected by $drm_crtc.commit_lock.

event

drm_pending_vblank_event pointer to clean up private events.

abort_completion

A flag that’s set after drm_atomic_helper_setup_commit() takes a second reference for the completion of $drm_crtc_state.event. It’s used by the free code to remove the second reference if commit fails.

Description

This structure is used to track pending modeset changes and atomic commit on a per-CRTC basis. Since updating the list should never block, this structure is reference counted to allow waiters to safely wait on an event to complete, without holding any locks.

It has 3 different events in total to allow a fine-grained synchronization between outstanding updates:

atomic commit thread                    hardware

write new state into hardware   ---->   ...
signal hw_done
                                        switch to new state on next
...                                     v/hblank

wait for buffers to show up             ...

...                                     send completion irq
                                        irq handler signals flip_done
cleanup old buffers

signal cleanup_done

wait for flip_done              <----
clean up atomic state

The important bit to know is that cleanup_done is the terminal event, but the ordering between flip_done and hw_done is entirely up to the specific driver and modeset state change.

For an implementation of how to use this look at drm_atomic_helper_setup_commit() from the atomic helper library.

Atomic Mode Setting IOCTL and UAPI Functions¶

This file contains the marshalling and demarshalling glue for the atomic UAPI in all its forms: The monster ATOMIC IOCTL itself, code for GET_PROPERTY and SET_PROPERTY IOCTLs. Plus interface functions for compatibility helpers and drivers which have special needs to construct their own atomic updates, e.g. for load detect or similar.

int drm_atomic_set_mode_for_crtc(struct drm_crtc_state *state, const struct drm_display_mode *mode)¶: set mode for CRTC

Parameters

struct drm_crtc_state *state: the CRTC whose incoming state to update
const struct drm_display_mode *mode: kernel-internal mode to use for the CRTC, or NULL to disable

Description

Set a mode (originating from the kernel) on the desired CRTC state and update the enable property.

Return

Zero on success, error code on failure. Cannot return -EDEADLK.

int drm_atomic_set_mode_prop_for_crtc(struct drm_crtc_state *state, struct drm_property_blob *blob)¶: set mode for CRTC

Parameters

struct drm_crtc_state *state: the CRTC whose incoming state to update
struct drm_property_blob *blob: pointer to blob property to use for mode

Description

Set a mode (originating from a blob property) on the desired CRTC state. This function will take a reference on the blob property for the CRTC state, and release the reference held on the state’s existing mode property, if any was set.

Return

Zero on success, error code on failure. Cannot return -EDEADLK.

int drm_atomic_set_crtc_for_plane(struct drm_plane_state *plane_state, struct drm_crtc *crtc)¶: set CRTC for plane

Parameters

struct drm_plane_state *plane_state: the plane whose incoming state to update
struct drm_crtc *crtc: CRTC to use for the plane

Description

Changing the assigned CRTC for a plane requires us to grab the lock and state for the new CRTC, as needed. This function takes care of all these details besides updating the pointer in the state object itself.

Return

0 on success or can fail with -EDEADLK or -ENOMEM. When the error is EDEADLK then the w/w mutex code has detected a deadlock and the entire atomic sequence must be restarted. All other errors are fatal.

void drm_atomic_set_fb_for_plane(struct drm_plane_state *plane_state, struct drm_framebuffer *fb)¶: set framebuffer for plane

Parameters

struct drm_plane_state *plane_state: atomic state object for the plane
struct drm_framebuffer *fb: fb to use for the plane

Description

Changing the assigned framebuffer for a plane requires us to grab a reference to the new fb and drop the reference to the old fb, if there is one. This function takes care of all these details besides updating the pointer in the state object itself.

int drm_atomic_set_crtc_for_connector(struct drm_connector_state *conn_state, struct drm_crtc *crtc)¶: set CRTC for connector

Parameters

struct drm_connector_state *conn_state: atomic state object for the connector
struct drm_crtc *crtc: CRTC to use for the connector

Description

Changing the assigned CRTC for a connector requires us to grab the lock and state for the new CRTC, as needed. This function takes care of all these details besides updating the pointer in the state object itself.

Return

0 on success or can fail with -EDEADLK or -ENOMEM. When the error is EDEADLK then the w/w mutex code has detected a deadlock and the entire atomic sequence must be restarted. All other errors are fatal.

CRTC Abstraction¶

A CRTC represents the overall display pipeline. It receives pixel data from drm_plane and blends them together. The drm_display_mode is also attached to the CRTC, specifying display timings. On the output side the data is fed to one or more drm_encoder, which are then each connected to one drm_connector.

To create a CRTC, a KMS drivers allocates and zeroes an instances of struct drm_crtc (possibly as part of a larger structure) and registers it with a call to drm_crtc_init_with_planes().

The CRTC is also the entry point for legacy modeset operations, see drm_crtc_funcs.set_config, legacy plane operations, see drm_crtc_funcs.page_flip and drm_crtc_funcs.cursor_set2, and other legacy operations like drm_crtc_funcs.gamma_set. For atomic drivers all these features are controlled through drm_property and drm_mode_config_funcs.atomic_check.

CRTC Functions Reference¶

struct drm_crtc_state¶: mutable CRTC state

Definition

struct drm_crtc_state {
  struct drm_crtc *crtc;
  bool enable;
  bool active;
  bool planes_changed : 1;
  bool mode_changed : 1;
  bool active_changed : 1;
  bool connectors_changed : 1;
  bool zpos_changed : 1;
  bool color_mgmt_changed : 1;
  bool no_vblank : 1;
  u32 plane_mask;
  u32 connector_mask;
  u32 encoder_mask;
  struct drm_display_mode adjusted_mode;
  struct drm_display_mode mode;
  struct drm_property_blob *mode_blob;
  struct drm_property_blob *degamma_lut;
  struct drm_property_blob *ctm;
  struct drm_property_blob *gamma_lut;
  u32 target_vblank;
  bool async_flip;
  bool vrr_enabled;
  bool self_refresh_active;
  enum drm_scaling_filter scaling_filter;
  struct drm_pending_vblank_event *event;
  struct drm_crtc_commit *commit;
  struct drm_atomic_state *state;
};

Members

crtc

backpointer to the CRTC

enable

Whether the CRTC should be enabled, gates all other state. This controls reservations of shared resources. Actual hardware state is controlled by active.

active

Whether the CRTC is actively displaying (used for DPMS). Implies that enable is set. The driver must not release any shared resources if active is set to false but enable still true, because userspace expects that a DPMS ON always succeeds.

Hence drivers must not consult active in their various drm_mode_config_funcs.atomic_check callback to reject an atomic commit. They can consult it to aid in the computation of derived hardware state, since even in the DPMS OFF state the display hardware should be as much powered down as when the CRTC is completely disabled through setting enable to false.

planes_changed

Planes on this crtc are updated. Used by the atomic helpers and drivers to steer the atomic commit control flow.

mode_changed

mode or enable has been changed. Used by the atomic helpers and drivers to steer the atomic commit control flow. See also drm_atomic_crtc_needs_modeset().

Drivers are supposed to set this for any CRTC state changes that require a full modeset. They can also reset it to false if e.g. a mode change can be done without a full modeset by only changing scaler settings.

active_changed

active has been toggled. Used by the atomic helpers and drivers to steer the atomic commit control flow. See also drm_atomic_crtc_needs_modeset().

connectors_changed

Connectors to this crtc have been updated, either in their state or routing. Used by the atomic helpers and drivers to steer the atomic commit control flow. See also drm_atomic_crtc_needs_modeset().

Drivers are supposed to set this as-needed from their own atomic check code, e.g. from drm_encoder_helper_funcs.atomic_check

zpos_changed

zpos values of planes on this crtc have been updated. Used by the atomic helpers and drivers to steer the atomic commit control flow.

color_mgmt_changed

Color management properties have changed (gamma_lut, degamma_lut or ctm). Used by the atomic helpers and drivers to steer the atomic commit control flow.

no_vblank

Reflects the ability of a CRTC to send VBLANK events. This state usually depends on the pipeline configuration. If set to true, DRM atomic helpers will send out a fake VBLANK event during display updates after all hardware changes have been committed. This is implemented in drm_atomic_helper_fake_vblank().

One usage is for drivers and/or hardware without support for VBLANK interrupts. Such drivers typically do not initialize vblanking (i.e., call drm_vblank_init() with the number of CRTCs). For CRTCs without initialized vblanking, this field is set to true in drm_atomic_helper_check_modeset(), and a fake VBLANK event will be send out on each update of the display pipeline by drm_atomic_helper_fake_vblank().

Another usage is CRTCs feeding a writeback connector operating in oneshot mode. In this case the fake VBLANK event is only generated when a job is queued to the writeback connector, and we want the core to fake VBLANK events when this part of the pipeline hasn’t changed but others had or when the CRTC and connectors are being disabled.

__drm_atomic_helper_crtc_duplicate_state() will not reset the value from the current state, the CRTC driver is then responsible for updating this field when needed.

Note that the combination of drm_crtc_state.event == NULL and drm_crtc_state.no_blank == true is valid and usually used when the writeback connector attached to the CRTC has a new job queued. In this case the driver will send the VBLANK event on its own when the writeback job is complete.

plane_mask

Bitmask of drm_plane_mask(plane) of planes attached to this CRTC.

connector_mask

Bitmask of drm_connector_mask(connector) of connectors attached to this CRTC.

encoder_mask

Bitmask of drm_encoder_mask(encoder) of encoders attached to this CRTC.

adjusted_mode

Internal display timings which can be used by the driver to handle differences between the mode requested by userspace in mode and what is actually programmed into the hardware.

For drivers using drm_bridge, this stores hardware display timings used between the CRTC and the first bridge. For other drivers, the meaning of the adjusted_mode field is purely driver implementation defined information, and will usually be used to store the hardware display timings used between the CRTC and encoder blocks.

mode

Display timings requested by userspace. The driver should try to match the refresh rate as close as possible (but note that it’s undefined what exactly is close enough, e.g. some of the HDMI modes only differ in less than 1% of the refresh rate). The active width and height as observed by userspace for positioning planes must match exactly.

For external connectors where the sink isn’t fixed (like with a built-in panel), this mode here should match the physical mode on the wire to the last details (i.e. including sync polarities and everything).

mode_blob

drm_property_blob for mode, for exposing the mode to atomic userspace.

degamma_lut

Lookup table for converting framebuffer pixel data before apply the color conversion matrix ctm. See drm_crtc_enable_color_mgmt(). The blob (if not NULL) is an array of struct drm_color_lut.

ctm

Color transformation matrix. See drm_crtc_enable_color_mgmt(). The blob (if not NULL) is a struct drm_color_ctm.

gamma_lut

Lookup table for converting pixel data after the color conversion matrix ctm. See drm_crtc_enable_color_mgmt(). The blob (if not NULL) is an array of struct drm_color_lut.

Note that for mostly historical reasons stemming from Xorg heritage, this is also used to store the color map (also sometimes color lut, CLUT or color palette) for indexed formats like DRM_FORMAT_C8.

target_vblank

Target vertical blank period when a page flip should take effect.

async_flip

This is set when DRM_MODE_PAGE_FLIP_ASYNC is set in the legacy PAGE_FLIP IOCTL. It’s not wired up for the atomic IOCTL itself yet.

vrr_enabled

Indicates if variable refresh rate should be enabled for the CRTC. Support for the requested vrr state will depend on driver and hardware capabiltiy - lacking support is not treated as failure.

self_refresh_active

Used by the self refresh helpers to denote when a self refresh transition is occurring. This will be set on enable/disable callbacks when self refresh is being enabled or disabled. In some cases, it may not be desirable to fully shut off the crtc during self refresh. CRTC’s can inspect this flag and determine the best course of action.

scaling_filter

Scaling filter to be applied

event

Optional pointer to a DRM event to signal upon completion of the state update. The driver must send out the event when the atomic commit operation completes. There are two cases:

The event is for a CRTC which is being disabled through this atomic commit. In that case the event can be send out any time after the hardware has stopped scanning out the current framebuffers. It should contain the timestamp and counter for the last vblank before the display pipeline was shut off. The simplest way to achieve that is calling drm_crtc_send_vblank_event() somewhen after drm_crtc_vblank_off() has been called.

For a CRTC which is enabled at the end of the commit (even when it undergoes an full modeset) the vblank timestamp and counter must be for the vblank right before the first frame that scans out the new set of buffers. Again the event can only be sent out after the hardware has stopped scanning out the old buffers.

Events for disabled CRTCs are not allowed, and drivers can ignore that case.

For very simple hardware without VBLANK interrupt, enabling struct drm_crtc_state.no_vblank makes DRM’s atomic commit helpers send a fake VBLANK event at the end of the display update after all hardware changes have been applied. See drm_atomic_helper_fake_vblank().

For more complex hardware this can be handled by the drm_crtc_send_vblank_event() function, which the driver should call on the provided event upon completion of the atomic commit. Note that if the driver supports vblank signalling and timestamping the vblank counters and timestamps must agree with the ones returned from page flip events. With the current vblank helper infrastructure this can be achieved by holding a vblank reference while the page flip is pending, acquired through drm_crtc_vblank_get() and released with drm_crtc_vblank_put(). Drivers are free to implement their own vblank counter and timestamp tracking though, e.g. if they have accurate timestamp registers in hardware.

For hardware which supports some means to synchronize vblank interrupt delivery with committing display state there’s also drm_crtc_arm_vblank_event(). See the documentation of that function for a detailed discussion of the constraints it needs to be used safely.

If the device can’t notify of flip completion in a race-free way at all, then the event should be armed just after the page flip is committed. In the worst case the driver will send the event to userspace one frame too late. This doesn’t allow for a real atomic update, but it should avoid tearing.

commit

This tracks how the commit for this update proceeds through the various phases. This is never cleared, except when we destroy the state, so that subsequent commits can synchronize with previous ones.

state

backpointer to global drm_atomic_state

Description

Note that the distinction between enable and active is rather subtle: Flipping active while enable is set without changing anything else may never return in a failure from the drm_mode_config_funcs.atomic_check callback. Userspace assumes that a DPMS On will always succeed. In other words: enable controls resource assignment, active controls the actual hardware state.

The three booleans active_changed, connectors_changed and mode_changed are intended to indicate whether a full modeset is needed, rather than strictly describing what has changed in a commit. See also: drm_atomic_crtc_needs_modeset()

WARNING: Transitional helpers (like drm_helper_crtc_mode_set() or drm_helper_crtc_mode_set_base()) do not maintain many of the derived control state like plane_mask so drivers not converted over to atomic helpers should not rely on these being accurate!

struct drm_crtc_funcs¶: control CRTCs for a given device

Definition

struct drm_crtc_funcs {
  void (*reset)(struct drm_crtc *crtc);
  int (*cursor_set)(struct drm_crtc *crtc, struct drm_file *file_priv, uint32_t handle, uint32_t width, uint32_t height);
  int (*cursor_set2)(struct drm_crtc *crtc, struct drm_file *file_priv,uint32_t handle, uint32_t width, uint32_t height, int32_t hot_x, int32_t hot_y);
  int (*cursor_move)(struct drm_crtc *crtc, int x, int y);
  int (*gamma_set)(struct drm_crtc *crtc, u16 *r, u16 *g, u16 *b,uint32_t size, struct drm_modeset_acquire_ctx *ctx);
  void (*destroy)(struct drm_crtc *crtc);
  int (*set_config)(struct drm_mode_set *set, struct drm_modeset_acquire_ctx *ctx);
  int (*page_flip)(struct drm_crtc *crtc,struct drm_framebuffer *fb,struct drm_pending_vblank_event *event,uint32_t flags, struct drm_modeset_acquire_ctx *ctx);
  int (*page_flip_target)(struct drm_crtc *crtc,struct drm_framebuffer *fb,struct drm_pending_vblank_event *event,uint32_t flags, uint32_t target, struct drm_modeset_acquire_ctx *ctx);
  int (*set_property)(struct drm_crtc *crtc, struct drm_property *property, uint64_t val);
  struct drm_crtc_state *(*atomic_duplicate_state)(struct drm_crtc *crtc);
  void (*atomic_destroy_state)(struct drm_crtc *crtc, struct drm_crtc_state *state);
  int (*atomic_set_property)(struct drm_crtc *crtc,struct drm_crtc_state *state,struct drm_property *property, uint64_t val);
  int (*atomic_get_property)(struct drm_crtc *crtc,const struct drm_crtc_state *state,struct drm_property *property, uint64_t *val);
  int (*late_register)(struct drm_crtc *crtc);
  void (*early_unregister)(struct drm_crtc *crtc);
  int (*set_crc_source)(struct drm_crtc *crtc, const char *source);
  int (*verify_crc_source)(struct drm_crtc *crtc, const char *source, size_t *values_cnt);
  const char *const *(*get_crc_sources)(struct drm_crtc *crtc, size_t *count);
  void (*atomic_print_state)(struct drm_printer *p, const struct drm_crtc_state *state);
  u32 (*get_vblank_counter)(struct drm_crtc *crtc);
  int (*enable_vblank)(struct drm_crtc *crtc);
  void (*disable_vblank)(struct drm_crtc *crtc);
  bool (*get_vblank_timestamp)(struct drm_crtc *crtc,int *max_error,ktime_t *vblank_time, bool in_vblank_irq);
};

Members

reset

Reset CRTC hardware and software state to off. This function isn’t called by the core directly, only through drm_mode_config_reset(). It’s not a helper hook only for historical reasons.

Atomic drivers can use drm_atomic_helper_crtc_reset() to reset atomic state using this hook.

cursor_set

Update the cursor image. The cursor position is relative to the CRTC and can be partially or fully outside of the visible area.

Note that contrary to all other KMS functions the legacy cursor entry points don’t take a framebuffer object, but instead take directly a raw buffer object id from the driver’s buffer manager (which is either GEM or TTM for current drivers).

This entry point is deprecated, drivers should instead implement universal plane support and register a proper cursor plane using drm_crtc_init_with_planes().

This callback is optional

RETURNS:

0 on success or a negative error code on failure.

cursor_set2

Update the cursor image, including hotspot information. The hotspot must not affect the cursor position in CRTC coordinates, but is only meant as a hint for virtualized display hardware to coordinate the guests and hosts cursor position. The cursor hotspot is relative to the cursor image. Otherwise this works exactly like cursor_set.

This entry point is deprecated, drivers should instead implement universal plane support and register a proper cursor plane using drm_crtc_init_with_planes().

This callback is optional.

RETURNS:

0 on success or a negative error code on failure.

cursor_move

Update the cursor position. The cursor does not need to be visible when this hook is called.

This entry point is deprecated, drivers should instead implement universal plane support and register a proper cursor plane using drm_crtc_init_with_planes().

This callback is optional.

RETURNS:

0 on success or a negative error code on failure.

gamma_set

Set gamma on the CRTC.

This callback is optional.

Atomic drivers who want to support gamma tables should implement the atomic color management support, enabled by calling drm_crtc_enable_color_mgmt(), which then supports the legacy gamma interface through the drm_atomic_helper_legacy_gamma_set() compatibility implementation.

destroy

Clean up CRTC resources. This is only called at driver unload time through drm_mode_config_cleanup() since a CRTC cannot be hotplugged in DRM.

set_config

This is the main legacy entry point to change the modeset state on a CRTC. All the details of the desired configuration are passed in a struct drm_mode_set - see there for details.

Drivers implementing atomic modeset should use drm_atomic_helper_set_config() to implement this hook.

RETURNS:

0 on success or a negative error code on failure.

page_flip

Legacy entry point to schedule a flip to the given framebuffer.

Page flipping is a synchronization mechanism that replaces the frame buffer being scanned out by the CRTC with a new frame buffer during vertical blanking, avoiding tearing (except when requested otherwise through the DRM_MODE_PAGE_FLIP_ASYNC flag). When an application requests a page flip the DRM core verifies that the new frame buffer is large enough to be scanned out by the CRTC in the currently configured mode and then calls this hook with a pointer to the new frame buffer.

The driver must wait for any pending rendering to the new framebuffer to complete before executing the flip. It should also wait for any pending rendering from other drivers if the underlying buffer is a shared dma-buf.

An application can request to be notified when the page flip has completed. The drm core will supply a struct drm_event in the event parameter in this case. This can be handled by the drm_crtc_send_vblank_event() function, which the driver should call on the provided event upon completion of the flip. Note that if the driver supports vblank signalling and timestamping the vblank counters and timestamps must agree with the ones returned from page flip events. With the current vblank helper infrastructure this can be achieved by holding a vblank reference while the page flip is pending, acquired through drm_crtc_vblank_get() and released with drm_crtc_vblank_put(). Drivers are free to implement their own vblank counter and timestamp tracking though, e.g. if they have accurate timestamp registers in hardware.

This callback is optional.

NOTE:

Very early versions of the KMS ABI mandated that the driver must block (but not reject) any rendering to the old framebuffer until the flip operation has completed and the old framebuffer is no longer visible. This requirement has been lifted, and userspace is instead expected to request delivery of an event and wait with recycling old buffers until such has been received.

RETURNS:

0 on success or a negative error code on failure. Note that if a page flip operation is already pending the callback should return -EBUSY. Pageflips on a disabled CRTC (either by setting a NULL mode or just runtime disabled through DPMS respectively the new atomic “ACTIVE” state) should result in an -EINVAL error code. Note that drm_atomic_helper_page_flip() checks this already for atomic drivers.

page_flip_target

Same as page_flip but with an additional parameter specifying the absolute target vertical blank period (as reported by drm_crtc_vblank_count()) when the flip should take effect.

Note that the core code calls drm_crtc_vblank_get before this entry point, and will call drm_crtc_vblank_put if this entry point returns any non-0 error code. It’s the driver’s responsibility to call drm_crtc_vblank_put after this entry point returns 0, typically when the flip completes.

set_property

This is the legacy entry point to update a property attached to the CRTC.

This callback is optional if the driver does not support any legacy driver-private properties. For atomic drivers it is not used because property handling is done entirely in the DRM core.

RETURNS:

0 on success or a negative error code on failure.

atomic_duplicate_state

Duplicate the current atomic state for this CRTC and return it. The core and helpers guarantee that any atomic state duplicated with this hook and still owned by the caller (i.e. not transferred to the driver by calling drm_mode_config_funcs.atomic_commit) will be cleaned up by calling the atomic_destroy_state hook in this structure.

This callback is mandatory for atomic drivers.

Atomic drivers which don’t subclass struct drm_crtc_state should use drm_atomic_helper_crtc_duplicate_state(). Drivers that subclass the state structure to extend it with driver-private state should use __drm_atomic_helper_crtc_duplicate_state() to make sure shared state is duplicated in a consistent fashion across drivers.

It is an error to call this hook before drm_crtc.state has been initialized correctly.

NOTE:

If the duplicate state references refcounted resources this hook must acquire a reference for each of them. The driver must release these references again in atomic_destroy_state.

RETURNS:

Duplicated atomic state or NULL when the allocation failed.

atomic_destroy_state

Destroy a state duplicated with atomic_duplicate_state and release or unreference all resources it references

This callback is mandatory for atomic drivers.

atomic_set_property

Decode a driver-private property value and store the decoded value into the passed-in state structure. Since the atomic core decodes all standardized properties (even for extensions beyond the core set of properties which might not be implemented by all drivers) this requires drivers to subclass the state structure.

Such driver-private properties should really only be implemented for truly hardware/vendor specific state. Instead it is preferred to standardize atomic extension and decode the properties used to expose such an extension in the core.

Do not call this function directly, use drm_atomic_crtc_set_property() instead.

This callback is optional if the driver does not support any driver-private atomic properties.

NOTE:

This function is called in the state assembly phase of atomic modesets, which can be aborted for any reason (including on userspace’s request to just check whether a configuration would be possible). Drivers MUST NOT touch any persistent state (hardware or software) or data structures except the passed in state parameter.

Also since userspace controls in which order properties are set this function must not do any input validation (since the state update is incomplete and hence likely inconsistent). Instead any such input validation must be done in the various atomic_check callbacks.

RETURNS:

0 if the property has been found, -EINVAL if the property isn’t implemented by the driver (which should never happen, the core only asks for properties attached to this CRTC). No other validation is allowed by the driver. The core already checks that the property value is within the range (integer, valid enum value, …) the driver set when registering the property.

atomic_get_property

Reads out the decoded driver-private property. This is used to implement the GETCRTC IOCTL.

Do not call this function directly, use drm_atomic_crtc_get_property() instead.

This callback is optional if the driver does not support any driver-private atomic properties.

RETURNS:

0 on success, -EINVAL if the property isn’t implemented by the driver (which should never happen, the core only asks for properties attached to this CRTC).

late_register

This optional hook can be used to register additional userspace interfaces attached to the crtc like debugfs interfaces. It is called late in the driver load sequence from drm_dev_register(). Everything added from this callback should be unregistered in the early_unregister callback.

Returns:

0 on success, or a negative error code on failure.

early_unregister

This optional hook should be used to unregister the additional userspace interfaces attached to the crtc from late_register. It is called from drm_dev_unregister(), early in the driver unload sequence to disable userspace access before data structures are torndown.

set_crc_source

Changes the source of CRC checksums of frames at the request of userspace, typically for testing purposes. The sources available are specific of each driver and a NULL value indicates that CRC generation is to be switched off.

When CRC generation is enabled, the driver should call drm_crtc_add_crc_entry() at each frame, providing any information that characterizes the frame contents in the crcN arguments, as provided from the configured source. Drivers must accept an “auto” source name that will select a default source for this CRTC.

This may trigger an atomic modeset commit if necessary, to enable CRC generation.

Note that “auto” can depend upon the current modeset configuration, e.g. it could pick an encoder or output specific CRC sampling point.

This callback is optional if the driver does not support any CRC generation functionality.

RETURNS:

0 on success or a negative error code on failure.

verify_crc_source

verifies the source of CRC checksums of frames before setting the source for CRC and during crc open. Source parameter can be NULL while disabling crc source.

This callback is optional if the driver does not support any CRC generation functionality.

RETURNS:

0 on success or a negative error code on failure.

get_crc_sources

Driver callback for getting a list of all the available sources for CRC generation. This callback depends upon verify_crc_source, So verify_crc_source callback should be implemented before implementing this. Driver can pass full list of available crc sources, this callback does the verification on each crc-source before passing it to userspace.

This callback is optional if the driver does not support exporting of possible CRC sources list.

RETURNS:

a constant character pointer to the list of all the available CRC sources. On failure driver should return NULL. count should be updated with number of sources in list. if zero we don’t process any source from the list.

atomic_print_state

If driver subclasses struct drm_crtc_state, it should implement this optional hook for printing additional driver specific state.

Do not call this directly, use drm_atomic_crtc_print_state() instead.

get_vblank_counter

Driver callback for fetching a raw hardware vblank counter for the CRTC. It’s meant to be used by new drivers as the replacement of drm_driver.get_vblank_counter hook.

This callback is optional. If a device doesn’t have a hardware counter, the driver can simply leave the hook as NULL. The DRM core will account for missed vblank events while interrupts where disabled based on system timestamps.

Wraparound handling and loss of events due to modesetting is dealt with in the DRM core code, as long as drivers call drm_crtc_vblank_off() and drm_crtc_vblank_on() when disabling or enabling a CRTC.

Returns:

Raw vblank counter value.

enable_vblank

Enable vblank interrupts for the CRTC. It’s meant to be used by new drivers as the replacement of drm_driver.enable_vblank hook.

Returns:

Zero on success, appropriate errno if the vblank interrupt cannot be enabled.

disable_vblank

Disable vblank interrupts for the CRTC. It’s meant to be used by new drivers as the replacement of drm_driver.disable_vblank hook.

get_vblank_timestamp

Called by drm_get_last_vbltimestamp(). Should return a precise timestamp when the most recent vblank interval ended or will end.

Specifically, the timestamp in vblank_time should correspond as closely as possible to the time when the first video scanline of the video frame after the end of vblank will start scanning out, the time immediately after end of the vblank interval. If the crtc is currently inside vblank, this will be a time in the future. If the crtc is currently scanning out a frame, this will be the past start time of the current scanout. This is meant to adhere to the OpenML OML_sync_control extension specification.

Parameters:

crtc:: CRTC for which timestamp should be returned.
max_error:: Maximum allowable timestamp error in nanoseconds. Implementation should strive to provide timestamp with an error of at most max_error nanoseconds. Returns true upper bound on error for timestamp.
vblank_time:: Target location for returned vblank timestamp.
in_vblank_irq:: True when called from drm_crtc_handle_vblank(). Some drivers need to apply some workarounds for gpu-specific vblank irq quirks if flag is set.

Returns:

True on success, false on failure, which means the core should fallback to a simple timestamp taken in drm_crtc_handle_vblank().

Description

The drm_crtc_funcs structure is the central CRTC management structure in the DRM. Each CRTC controls one or more connectors (note that the name CRTC is simply historical, a CRTC may control LVDS, VGA, DVI, TV out, etc. connectors, not just CRTs).

Each driver is responsible for filling out this structure at startup time, in addition to providing other modesetting features, like i2c and DDC bus accessors.

struct drm_crtc¶: central CRTC control structure

Definition

struct drm_crtc {
  struct drm_device *dev;
  struct device_node *port;
  struct list_head head;
  char *name;
  struct drm_modeset_lock mutex;
  struct drm_mode_object base;
  struct drm_plane *primary;
  struct drm_plane *cursor;
  unsigned index;
  int cursor_x;
  int cursor_y;
  bool enabled;
  struct drm_display_mode mode;
  struct drm_display_mode hwmode;
  int x;
  int y;
  const struct drm_crtc_funcs *funcs;
  uint32_t gamma_size;
  uint16_t *gamma_store;
  const struct drm_crtc_helper_funcs *helper_private;
  struct drm_object_properties properties;
  struct drm_property *scaling_filter_property;
  struct drm_crtc_state *state;
  struct list_head commit_list;
  spinlock_t commit_lock;
  struct dentry *debugfs_entry;
  struct drm_crtc_crc crc;
  unsigned int fence_context;
  spinlock_t fence_lock;
  unsigned long fence_seqno;
  char timeline_name[32];
  struct drm_self_refresh_data *self_refresh_data;
};

Members

dev

parent DRM device

port

OF node used by drm_of_find_possible_crtcs().

head

List of all CRTCs on dev, linked from drm_mode_config.crtc_list. Invariant over the lifetime of dev and therefore does not need locking.

name

human readable name, can be overwritten by the driver

mutex

This provides a read lock for the overall CRTC state (mode, dpms state, …) and a write lock for everything which can be update without a full modeset (fb, cursor data, CRTC properties …). A full modeset also need to grab drm_mode_config.connection_mutex.

For atomic drivers specifically this protects state.

base

base KMS object for ID tracking etc.

primary

Primary plane for this CRTC. Note that this is only relevant for legacy IOCTL, it specifies the plane implicitly used by the SETCRTC and PAGE_FLIP IOCTLs. It does not have any significance beyond that.

cursor

Cursor plane for this CRTC. Note that this is only relevant for legacy IOCTL, it specifies the plane implicitly used by the SETCURSOR and SETCURSOR2 IOCTLs. It does not have any significance beyond that.

index

Position inside the mode_config.list, can be used as an array index. It is invariant over the lifetime of the CRTC.

cursor_x

Current x position of the cursor, used for universal cursor planes because the SETCURSOR IOCTL only can update the framebuffer without supplying the coordinates. Drivers should not use this directly, atomic drivers should look at drm_plane_state.crtc_x of the cursor plane instead.

cursor_y

Current y position of the cursor, used for universal cursor planes because the SETCURSOR IOCTL only can update the framebuffer without supplying the coordinates. Drivers should not use this directly, atomic drivers should look at drm_plane_state.crtc_y of the cursor plane instead.

enabled

Is this CRTC enabled? Should only be used by legacy drivers, atomic drivers should instead consult drm_crtc_state.enable and drm_crtc_state.active. Atomic drivers can update this by calling drm_atomic_helper_update_legacy_modeset_state().

mode

Current mode timings. Should only be used by legacy drivers, atomic drivers should instead consult drm_crtc_state.mode. Atomic drivers can update this by calling drm_atomic_helper_update_legacy_modeset_state().

hwmode

Programmed mode in hw, after adjustments for encoders, crtc, panel scaling etc. Should only be used by legacy drivers, for high precision vblank timestamps in drm_crtc_vblank_helper_get_vblank_timestamp().

Note that atomic drivers should not use this, but instead use drm_crtc_state.adjusted_mode. And for high-precision timestamps drm_crtc_vblank_helper_get_vblank_timestamp() used drm_vblank_crtc.hwmode, which is filled out by calling drm_calc_timestamping_constants().

x

x position on screen. Should only be used by legacy drivers, atomic drivers should look at drm_plane_state.crtc_x of the primary plane instead. Updated by calling drm_atomic_helper_update_legacy_modeset_state().

y

y position on screen. Should only be used by legacy drivers, atomic drivers should look at drm_plane_state.crtc_y of the primary plane instead. Updated by calling drm_atomic_helper_update_legacy_modeset_state().

funcs

CRTC control functions

gamma_size

Size of legacy gamma ramp reported to userspace. Set up by calling drm_mode_crtc_set_gamma_size().

Note that atomic drivers need to instead use drm_crtc_state.gamma_lut. See drm_crtc_enable_color_mgmt().

gamma_store

Gamma ramp values used by the legacy SETGAMMA and GETGAMMA IOCTls. Set up by calling drm_mode_crtc_set_gamma_size().

Note that atomic drivers need to instead use drm_crtc_state.gamma_lut. See drm_crtc_enable_color_mgmt().

helper_private

mid-layer private data

properties

property tracking for this CRTC

scaling_filter_property

property to apply a particular filter while scaling.

state

Current atomic state for this CRTC.

This is protected by mutex. Note that nonblocking atomic commits access the current CRTC state without taking locks. Either by going through the struct drm_atomic_state pointers, see for_each_oldnew_crtc_in_state(), for_each_old_crtc_in_state() and for_each_new_crtc_in_state(). Or through careful ordering of atomic commit operations as implemented in the atomic helpers, see struct drm_crtc_commit.

commit_list

List of drm_crtc_commit structures tracking pending commits. Protected by commit_lock. This list holds its own full reference, as does the ongoing commit.

“Note that the commit for a state change is also tracked in drm_crtc_state.commit. For accessing the immediately preceding commit in an atomic update it is recommended to just use that pointer in the old CRTC state, since accessing that doesn’t need any locking or list-walking. commit_list should only be used to stall for framebuffer cleanup that’s signalled through drm_crtc_commit.cleanup_done.”

commit_lock

Spinlock to protect commit_list.

debugfs_entry

Debugfs directory for this CRTC.

crc

Configuration settings of CRC capture.

fence_context

timeline context used for fence operations.

fence_lock

spinlock to protect the fences in the fence_context.

fence_seqno

Seqno variable used as monotonic counter for the fences created on the CRTC’s timeline.

timeline_name

The name of the CRTC’s fence timeline.

self_refresh_data

Holds the state for the self refresh helpers

Initialized via drm_self_refresh_helper_init().

Description

Each CRTC may have one or more connectors associated with it. This structure allows the CRTC to be controlled.

struct drm_mode_set¶: new values for a CRTC config change

Definition

struct drm_mode_set {
  struct drm_framebuffer *fb;
  struct drm_crtc *crtc;
  struct drm_display_mode *mode;
  uint32_t x;
  uint32_t y;
  struct drm_connector **connectors;
  size_t num_connectors;
};

Members

fb: framebuffer to use for new config
crtc: CRTC whose configuration we’re about to change
mode: mode timings to use
x: position of this CRTC relative to fb
y: position of this CRTC relative to fb
connectors: array of connectors to drive with this CRTC if possible
num_connectors: size of connectors array

Description

This represents a modeset configuration for the legacy SETCRTC ioctl and is also used internally. Atomic drivers instead use drm_atomic_state.

drmm_crtc_alloc_with_planes¶

drmm_crtc_alloc_with_planes (dev, type, member, primary, cursor, funcs, name, ...)

Allocate and initialize a new CRTC object with specified primary and cursor planes.

Parameters

dev: DRM device
type: the type of the struct which contains struct drm_crtc
member: the name of the drm_crtc within type.
primary: Primary plane for CRTC
cursor: Cursor plane for CRTC
funcs: callbacks for the new CRTC
name: printf style format string for the CRTC name, or NULL for default name
...: variable arguments

Description

Allocates and initializes a new crtc object. Cleanup is automatically handled through registering drmm_crtc_cleanup() with drmm_add_action().

The drm_crtc_funcs.destroy hook must be NULL.

Return

Pointer to new crtc, or ERR_PTR on failure.

unsigned int drm_crtc_index(const struct drm_crtc *crtc)¶: find the index of a registered CRTC

Parameters

const struct drm_crtc *crtc: CRTC to find index for

Description

Given a registered CRTC, return the index of that CRTC within a DRM device’s list of CRTCs.

uint32_t drm_crtc_mask(const struct drm_crtc *crtc)¶: find the mask of a registered CRTC

Parameters

const struct drm_crtc *crtc: CRTC to find mask for

Description

Given a registered CRTC, return the mask bit of that CRTC for the drm_encoder.possible_crtcs and drm_plane.possible_crtcs fields.

struct drm_crtc *drm_crtc_find(struct drm_device *dev, struct drm_file *file_priv, uint32_t id)¶: look up a CRTC object from its ID

Parameters

struct drm_device *dev: DRM device
struct drm_file *file_priv: drm file to check for lease against.
uint32_t id: drm_mode_object ID

Description

This can be used to look up a CRTC from its userspace ID. Only used by drivers for legacy IOCTLs and interface, nowadays extensions to the KMS userspace interface should be done using drm_property.

drm_for_each_crtc¶

drm_for_each_crtc (crtc, dev)

iterate over all CRTCs

Parameters

crtc: a struct drm_crtc as the loop cursor
dev: the struct drm_device

Description

Iterate over all CRTCs of dev.

drm_for_each_crtc_reverse¶

drm_for_each_crtc_reverse (crtc, dev)

iterate over all CRTCs in reverse order

Parameters

crtc: a struct drm_crtc as the loop cursor
dev: the struct drm_device

Description

Iterate over all CRTCs of dev.

struct drm_crtc *drm_crtc_from_index(struct drm_device *dev, int idx)¶: find the registered CRTC at an index

Parameters

struct drm_device *dev: DRM device
int idx: index of registered CRTC to find for

Description

Given a CRTC index, return the registered CRTC from DRM device’s list of CRTCs with matching index. This is the inverse of drm_crtc_index(). It’s useful in the vblank callbacks (like drm_driver.enable_vblank or drm_driver.disable_vblank), since that still deals with indices instead of pointers to struct drm_crtc.”

int drm_crtc_init_with_planes(struct drm_device *dev, struct drm_crtc *crtc, struct drm_plane *primary, struct drm_plane *cursor, const struct drm_crtc_funcs *funcs, const char *name, ...)¶: Initialise a new CRTC object with specified primary and cursor planes.

Parameters

struct drm_device *dev: DRM device
struct drm_crtc *crtc: CRTC object to init
struct drm_plane *primary: Primary plane for CRTC
struct drm_plane *cursor: Cursor plane for CRTC
const struct drm_crtc_funcs *funcs: callbacks for the new CRTC
const char *name: printf style format string for the CRTC name, or NULL for default name
...: variable arguments

Description

Inits a new object created as base part of a driver crtc object. Drivers should use this function instead of drm_crtc_init(), which is only provided for backwards compatibility with drivers which do not yet support universal planes). For really simple hardware which has only 1 plane look at drm_simple_display_pipe_init() instead. The drm_crtc_funcs.destroy hook should call drm_crtc_cleanup() and kfree() the crtc structure. The crtc structure should not be allocated with devm_kzalloc().

The primary and cursor planes are only relevant for legacy uAPI, see drm_crtc.primary and drm_crtc.cursor.

Note

consider using drmm_crtc_alloc_with_planes() or drmm_crtc_init_with_planes() instead of drm_crtc_init_with_planes() to let the DRM managed resource infrastructure take care of cleanup and deallocation.

Return

Zero on success, error code on failure.

int drmm_crtc_init_with_planes(struct drm_device *dev, struct drm_crtc *crtc, struct drm_plane *primary, struct drm_plane *cursor, const struct drm_crtc_funcs *funcs, const char *name, ...)¶: Initialise a new CRTC object with specified primary and cursor planes.

Parameters

struct drm_device *dev: DRM device
struct drm_crtc *crtc: CRTC object to init
struct drm_plane *primary: Primary plane for CRTC
struct drm_plane *cursor: Cursor plane for CRTC
const struct drm_crtc_funcs *funcs: callbacks for the new CRTC
const char *name: printf style format string for the CRTC name, or NULL for default name
...: variable arguments

Description

Inits a new object created as base part of a driver crtc object. Drivers should use this function instead of drm_crtc_init(), which is only provided for backwards compatibility with drivers which do not yet support universal planes). For really simple hardware which has only 1 plane look at drm_simple_display_pipe_init() instead.

Cleanup is automatically handled through registering drmm_crtc_cleanup() with drmm_add_action(). The crtc structure should be allocated with drmm_kzalloc().

The drm_crtc_funcs.destroy hook must be NULL.

The primary and cursor planes are only relevant for legacy uAPI, see drm_crtc.primary and drm_crtc.cursor.

Return

Zero on success, error code on failure.

void drm_crtc_cleanup(struct drm_crtc *crtc)¶: Clean up the core crtc usage

Parameters

struct drm_crtc *crtc: CRTC to cleanup

Description

This function cleans up crtc and removes it from the DRM mode setting core. Note that the function does not free the crtc structure itself, this is the responsibility of the caller.

int drm_mode_set_config_internal(struct drm_mode_set *set)¶: helper to call drm_mode_config_funcs.set_config

Parameters

struct drm_mode_set *set: modeset config to set

Description

This is a little helper to wrap internal calls to the drm_mode_config_funcs.set_config driver interface. The only thing it adds is correct refcounting dance.

This should only be used by non-atomic legacy drivers.

Return

Zero on success, negative errno on failure.

int drm_crtc_check_viewport(const struct drm_crtc *crtc, int x, int y, const struct drm_display_mode *mode, const struct drm_framebuffer *fb)¶: Checks that a framebuffer is big enough for the CRTC viewport

Parameters

const struct drm_crtc *crtc: CRTC that framebuffer will be displayed on
int x: x panning
int y: y panning
const struct drm_display_mode *mode: mode that framebuffer will be displayed under
const struct drm_framebuffer *fb: framebuffer to check size of

int drm_crtc_create_scaling_filter_property(struct drm_crtc *crtc, unsigned int supported_filters)¶: create a new scaling filter property

Parameters

struct drm_crtc *crtc: drm CRTC
unsigned int supported_filters: bitmask of supported scaling filters, must include BIT(DRM_SCALING_FILTER_DEFAULT).

Description

This function lets driver to enable the scaling filter property on a given CRTC.

Return

Zero for success or -errno

Color Management Functions Reference¶

u64 drm_color_ctm_s31_32_to_qm_n(u64 user_input, u32 m, u32 n)¶

Parameters

u64 user_input: input value
u32 m: number of integer bits, only support m <= 32, include the sign-bit
u32 n: number of fractional bits, only support n <= 32

Description

Convert and clamp S31.32 sign-magnitude to Qm.n (signed 2’s complement). The sign-bit BIT(m+n-1) and above are 0 for positive value and 1 for negative the range of value is [-2^(m-1), 2^(m-1) - 2^-n]

For example A Q3.12 format number: - required bit: 3 + 12 = 15bits - range: [-2^2, 2^2 - 2^−15]

NOTE

the m can be zero if all bit_precision are used to present fractional: bits like Q0.32

void drm_crtc_enable_color_mgmt(struct drm_crtc *crtc, uint degamma_lut_size, bool has_ctm, uint gamma_lut_size)¶: enable color management properties

Parameters

struct drm_crtc *crtc: DRM CRTC
uint degamma_lut_size: the size of the degamma lut (before CSC)
bool has_ctm: whether to attach ctm_property for CSC matrix
uint gamma_lut_size: the size of the gamma lut (after CSC)

Description

This function lets the driver enable the color correction properties on a CRTC. This includes 3 degamma, csc and gamma properties that userspace can set and 2 size properties to inform the userspace of the lut sizes. Each of the properties are optional. The gamma and degamma properties are only attached if their size is not 0 and ctm_property is only attached if has_ctm is true.

int drm_mode_crtc_set_gamma_size(struct drm_crtc *crtc, int gamma_size)¶: set the gamma table size

Parameters

struct drm_crtc *crtc: CRTC to set the gamma table size for
int gamma_size: size of the gamma table

Description

Drivers which support gamma tables should set this to the supported gamma table size when initializing the CRTC. Currently the drm core only supports a fixed gamma table size.

Return

Zero on success, negative errno on failure.

int drm_plane_create_color_properties(struct drm_plane *plane, u32 supported_encodings, u32 supported_ranges, enum drm_color_encoding default_encoding, enum drm_color_range default_range)¶: color encoding related plane properties

Parameters

struct drm_plane *plane: plane object
u32 supported_encodings: bitfield indicating supported color encodings
u32 supported_ranges: bitfileld indicating supported color ranges
enum drm_color_encoding default_encoding: default color encoding
enum drm_color_range default_range: default color range

Description

Create and attach plane specific COLOR_ENCODING and COLOR_RANGE properties to plane. The supported encodings and ranges should be provided in supported_encodings and supported_ranges bitmasks. Each bit set in the bitmask indicates that its number as enum value is supported.

int drm_color_lut_check(const struct drm_property_blob *lut, u32 tests)¶: check validity of lookup table

Parameters

const struct drm_property_blob *lut: property blob containing LUT to check
u32 tests: bitmask of tests to run

Description

Helper to check whether a userspace-provided lookup table is valid and satisfies hardware requirements. Drivers pass a bitmask indicating which of the tests in drm_color_lut_tests should be performed.

Returns 0 on success, -EINVAL on failure.

u32 drm_color_lut_extract(u32 user_input, int bit_precision)¶: clamp and round LUT entries

Parameters

u32 user_input: input value
int bit_precision: number of bits the hw LUT supports

Description

Extract a degamma/gamma LUT value provided by user (in the form of drm_color_lut entries) and round it to the precision supported by the hardware.

int drm_color_lut_size(const struct drm_property_blob *blob)¶: calculate the number of entries in the LUT

Parameters

const struct drm_property_blob *blob: blob containing the LUT

Return

The number of entries in the color LUT stored in blob.

enum drm_color_lut_tests¶: hw-specific LUT tests to perform

Constants

DRM_COLOR_LUT_EQUAL_CHANNELS: Checks whether the entries of a LUT all have equal values for the red, green, and blue channels. Intended for hardware that only accepts a single value per LUT entry and assumes that value applies to all three color components.
DRM_COLOR_LUT_NON_DECREASING: Checks whether the entries of a LUT are always flat or increasing (never decreasing).

Description

The drm_color_lut_check() function takes a bitmask of the values here to determine which tests to apply to a userspace-provided LUT.

Frame Buffer Abstraction¶

Frame buffers are abstract memory objects that provide a source of pixels to scanout to a CRTC. Applications explicitly request the creation of frame buffers through the DRM_IOCTL_MODE_ADDFB(2) ioctls and receive an opaque handle that can be passed to the KMS CRTC control, plane configuration and page flip functions.

Frame buffers rely on the underlying memory manager for allocating backing storage. When creating a frame buffer applications pass a memory handle (or a list of memory handles for multi-planar formats) through the struct drm_mode_fb_cmd2 argument. For drivers using GEM as their userspace buffer management interface this would be a GEM handle. Drivers are however free to use their own backing storage object handles, e.g. vmwgfx directly exposes special TTM handles to userspace and so expects TTM handles in the create ioctl and not GEM handles.

Framebuffers are tracked with struct drm_framebuffer. They are published using drm_framebuffer_init() - after calling that function userspace can use and access the framebuffer object. The helper function drm_helper_mode_fill_fb_struct() can be used to pre-fill the required metadata fields.

The lifetime of a drm framebuffer is controlled with a reference count, drivers can grab additional references with drm_framebuffer_get() and drop them again with drm_framebuffer_put(). For driver-private framebuffers for which the last reference is never dropped (e.g. for the fbdev framebuffer when the struct struct drm_framebuffer is embedded into the fbdev helper struct) drivers can manually clean up a framebuffer at module unload time with drm_framebuffer_unregister_private(). But doing this is not recommended, and it’s better to have a normal free-standing struct drm_framebuffer.

Frame Buffer Functions Reference¶

struct drm_framebuffer_funcs¶: framebuffer hooks

Definition

struct drm_framebuffer_funcs {
  void (*destroy)(struct drm_framebuffer *framebuffer);
  int (*create_handle)(struct drm_framebuffer *fb,struct drm_file *file_priv, unsigned int *handle);
  int (*dirty)(struct drm_framebuffer *framebuffer,struct drm_file *file_priv, unsigned flags,unsigned color, struct drm_clip_rect *clips, unsigned num_clips);
};

Members

destroy

Clean up framebuffer resources, specifically also unreference the backing storage. The core guarantees to call this function for every framebuffer successfully created by calling drm_mode_config_funcs.fb_create. Drivers must also call drm_framebuffer_cleanup() to release DRM core resources for this framebuffer.

create_handle

Create a buffer handle in the driver-specific buffer manager (either GEM or TTM) valid for the passed-in struct drm_file. This is used by the core to implement the GETFB IOCTL, which returns (for sufficiently priviledged user) also a native buffer handle. This can be used for seamless transitions between modesetting clients by copying the current screen contents to a private buffer and blending between that and the new contents.

GEM based drivers should call drm_gem_handle_create() to create the handle.

RETURNS:

0 on success or a negative error code on failure.

dirty

Optional callback for the dirty fb IOCTL.

Userspace can notify the driver via this callback that an area of the framebuffer has changed and should be flushed to the display hardware. This can also be used internally, e.g. by the fbdev emulation, though that’s not the case currently.

See documentation in drm_mode.h for the struct drm_mode_fb_dirty_cmd for more information as all the semantics and arguments have a one to one mapping on this function.

Atomic drivers should use drm_atomic_helper_dirtyfb() to implement this hook.

RETURNS:

0 on success or a negative error code on failure.

struct drm_framebuffer¶: frame buffer object

Definition

struct drm_framebuffer {
  struct drm_device *dev;
  struct list_head head;
  struct drm_mode_object base;
  char comm[TASK_COMM_LEN];
  const struct drm_format_info *format;
  const struct drm_framebuffer_funcs *funcs;
  unsigned int pitches[DRM_FORMAT_MAX_PLANES];
  unsigned int offsets[DRM_FORMAT_MAX_PLANES];
  uint64_t modifier;
  unsigned int width;
  unsigned int height;
  int flags;
  int hot_x;
  int hot_y;
  struct list_head filp_head;
  struct drm_gem_object *obj[DRM_FORMAT_MAX_PLANES];
};

Members

dev

DRM device this framebuffer belongs to

head

Place on the drm_mode_config.fb_list, access protected by drm_mode_config.fb_lock.

base

base modeset object structure, contains the reference count.

comm

Name of the process allocating the fb, used for fb dumping.

format

framebuffer format information

funcs

framebuffer vfunc table

pitches

Line stride per buffer. For userspace created object this is copied from drm_mode_fb_cmd2.

offsets

Offset from buffer start to the actual pixel data in bytes, per buffer. For userspace created object this is copied from drm_mode_fb_cmd2.

Note that this is a linear offset and does not take into account tiling or buffer layout per modifier. It is meant to be used when the actual pixel data for this framebuffer plane starts at an offset, e.g. when multiple planes are allocated within the same backing storage buffer object. For tiled layouts this generally means its offsets must at least be tile-size aligned, but hardware often has stricter requirements.

This should not be used to specifiy x/y pixel offsets into the buffer data (even for linear buffers). Specifying an x/y pixel offset is instead done through the source rectangle in struct drm_plane_state.

modifier

Data layout modifier. This is used to describe tiling, or also special layouts (like compression) of auxiliary buffers. For userspace created object this is copied from drm_mode_fb_cmd2.

width

Logical width of the visible area of the framebuffer, in pixels.

height

Logical height of the visible area of the framebuffer, in pixels.

flags

Framebuffer flags like DRM_MODE_FB_INTERLACED or DRM_MODE_FB_MODIFIERS.

hot_x

X coordinate of the cursor hotspot. Used by the legacy cursor IOCTL when the driver supports cursor through a DRM_PLANE_TYPE_CURSOR universal plane.

hot_y

Y coordinate of the cursor hotspot. Used by the legacy cursor IOCTL when the driver supports cursor through a DRM_PLANE_TYPE_CURSOR universal plane.

filp_head

Placed on drm_file.fbs, protected by drm_file.fbs_lock.

obj

GEM objects backing the framebuffer, one per plane (optional).

This is used by the GEM framebuffer helpers, see e.g. drm_gem_fb_create().

Description

Note that the fb is refcounted for the benefit of driver internals, for example some hw, disabling a CRTC/plane is asynchronous, and scanout does not actually complete until the next vblank. So some cleanup (like releasing the reference(s) on the backing GEM bo(s)) should be deferred. In cases like this, the driver would like to hold a ref to the fb even though it has already been removed from userspace perspective. See drm_framebuffer_get() and drm_framebuffer_put().

The refcount is stored inside the mode object base.

void drm_framebuffer_get(struct drm_framebuffer *fb)¶: acquire a framebuffer reference

Parameters

struct drm_framebuffer *fb: DRM framebuffer

Description

This function increments the framebuffer’s reference count.

void drm_framebuffer_put(struct drm_framebuffer *fb)¶: release a framebuffer reference

Parameters

struct drm_framebuffer *fb: DRM framebuffer

Description

This function decrements the framebuffer’s reference count and frees the framebuffer if the reference count drops to zero.

uint32_t drm_framebuffer_read_refcount(const struct drm_framebuffer *fb)¶: read the framebuffer reference count.

Parameters

const struct drm_framebuffer *fb: framebuffer

Description

This functions returns the framebuffer’s reference count.

void drm_framebuffer_assign(struct drm_framebuffer **p, struct drm_framebuffer *fb)¶: store a reference to the fb

Parameters

struct drm_framebuffer **p: location to store framebuffer
struct drm_framebuffer *fb: new framebuffer (maybe NULL)

Description

This functions sets the location to store a reference to the framebuffer, unreferencing the framebuffer that was previously stored in that location.

struct drm_afbc_framebuffer¶: a special afbc frame buffer object

Definition

struct drm_afbc_framebuffer {
  struct drm_framebuffer base;
  u32 block_width;
  u32 block_height;
  u32 aligned_width;
  u32 aligned_height;
  u32 offset;
  u32 afbc_size;
};

Members

base: base framebuffer structure.
block_width: width of a single afbc block
block_height: height of a single afbc block
aligned_width: aligned frame buffer width
aligned_height: aligned frame buffer height
offset: offset of the first afbc header
afbc_size: minimum size of afbc buffer

Description

A derived class of struct drm_framebuffer, dedicated for afbc use cases.

int drm_framebuffer_init(struct drm_device *dev, struct drm_framebuffer *fb, const struct drm_framebuffer_funcs *funcs)¶: initialize a framebuffer

Parameters

struct drm_device *dev: DRM device
struct drm_framebuffer *fb: framebuffer to be initialized
const struct drm_framebuffer_funcs *funcs: … with these functions

Description

Allocates an ID for the framebuffer’s parent mode object, sets its mode functions & device file and adds it to the master fd list.

IMPORTANT: This functions publishes the fb and makes it available for concurrent access by other users. Which means by this point the fb _must_ be fully set up - since all the fb attributes are invariant over its lifetime, no further locking but only correct reference counting is required.

Return

Zero on success, error code on failure.

struct drm_framebuffer *drm_framebuffer_lookup(struct drm_device *dev, struct drm_file *file_priv, uint32_t id)¶: look up a drm framebuffer and grab a reference

Parameters

struct drm_device *dev: drm device
struct drm_file *file_priv: drm file to check for lease against.
uint32_t id: id of the fb object

Description

If successful, this grabs an additional reference to the framebuffer - callers need to make sure to eventually unreference the returned framebuffer again, using drm_framebuffer_put().

void drm_framebuffer_unregister_private(struct drm_framebuffer *fb)¶: unregister a private fb from the lookup idr

Parameters

struct drm_framebuffer *fb: fb to unregister

Description

Drivers need to call this when cleaning up driver-private framebuffers, e.g. those used for fbdev. Note that the caller must hold a reference of its own, i.e. the object may not be destroyed through this call (since it’ll lead to a locking inversion).

NOTE

This function is deprecated. For driver-private framebuffers it is not recommended to embed a framebuffer struct info fbdev struct, instead, a framebuffer pointer is preferred and drm_framebuffer_put() should be called when the framebuffer is to be cleaned up.

void drm_framebuffer_cleanup(struct drm_framebuffer *fb)¶: remove a framebuffer object

Parameters

struct drm_framebuffer *fb: framebuffer to remove

Description

Cleanup framebuffer. This function is intended to be used from the drivers drm_framebuffer_funcs.destroy callback. It can also be used to clean up driver private framebuffers embedded into a larger structure.

Note that this function does not remove the fb from active usage - if it is still used anywhere, hilarity can ensue since userspace could call getfb on the id and get back -EINVAL. Obviously no concern at driver unload time.

Also, the framebuffer will not be removed from the lookup idr - for user-created framebuffers this will happen in the rmfb ioctl. For driver-private objects (e.g. for fbdev) drivers need to explicitly call drm_framebuffer_unregister_private.

void drm_framebuffer_remove(struct drm_framebuffer *fb)¶: remove and unreference a framebuffer object

Parameters

struct drm_framebuffer *fb: framebuffer to remove

Description

Scans all the CRTCs and planes in dev’s mode_config. If they’re using fb, removes it, setting it to NULL. Then drops the reference to the passed-in framebuffer. Might take the modeset locks.

Note that this function optimizes the cleanup away if the caller holds the last reference to the framebuffer. It is also guaranteed to not take the modeset locks in this case.

int drm_framebuffer_plane_width(int width, const struct drm_framebuffer *fb, int plane)¶: width of the plane given the first plane

Parameters

int width: width of the first plane
const struct drm_framebuffer *fb: the framebuffer
int plane: plane index

Return

The width of plane, given that the width of the first plane is width.

int drm_framebuffer_plane_height(int height, const struct drm_framebuffer *fb, int plane)¶: height of the plane given the first plane

Parameters

int height: height of the first plane
const struct drm_framebuffer *fb: the framebuffer
int plane: plane index

Return

The height of plane, given that the height of the first plane is height.

DRM Format Handling¶

In the DRM subsystem, framebuffer pixel formats are described using the fourcc codes defined in include/uapi/drm/drm_fourcc.h. In addition to the fourcc code, a Format Modifier may optionally be provided, in order to further describe the buffer’s format - for example tiling or compression.

Format Modifiers¶

Format modifiers are used in conjunction with a fourcc code, forming a unique fourcc:modifier pair. This format:modifier pair must fully define the format and data layout of the buffer, and should be the only way to describe that particular buffer.

Having multiple fourcc:modifier pairs which describe the same layout should be avoided, as such aliases run the risk of different drivers exposing different names for the same data format, forcing userspace to understand that they are aliases.

Format modifiers may change any property of the buffer, including the number of planes and/or the required allocation size. Format modifiers are vendor-namespaced, and as such the relationship between a fourcc code and a modifier is specific to the modifer being used. For example, some modifiers may preserve meaning - such as number of planes - from the fourcc code, whereas others may not.

Modifiers must uniquely encode buffer layout. In other words, a buffer must match only a single modifier. A modifier must not be a subset of layouts of another modifier. For instance, it’s incorrect to encode pitch alignment in a modifier: a buffer may match a 64-pixel aligned modifier and a 32-pixel aligned modifier. That said, modifiers can have implicit minimal requirements.

For modifiers where the combination of fourcc code and modifier can alias, a canonical pair needs to be defined and used by all drivers. Preferred combinations are also encouraged where all combinations might lead to confusion and unnecessarily reduced interoperability. An example for the latter is AFBC, where the ABGR layouts are preferred over ARGB layouts.

There are two kinds of modifier users:

Kernel and user-space drivers: for drivers it’s important that modifiers don’t alias, otherwise two drivers might support the same format but use different aliases, preventing them from sharing buffers in an efficient format.
Higher-level programs interfacing with KMS/GBM/EGL/Vulkan/etc: these users see modifiers as opaque tokens they can check for equality and intersect. These users musn’t need to know to reason about the modifier value (i.e. they are not expected to extract information out of the modifier).

Vendors should document their modifier usage in as much detail as possible, to ensure maximum compatibility across devices, drivers and applications.

The authoritative list of format modifier codes is found in include/uapi/drm/drm_fourcc.h

Format Functions Reference¶

DRM_FORMAT_MAX_PLANES¶

DRM_FORMAT_MAX_PLANES ()

maximum number of planes a DRM format can have

Parameters

struct drm_format_info¶: information about a DRM format

Definition

struct drm_format_info {
  u32 format;
  u8 depth;
  u8 num_planes;
  union {
    u8 cpp[DRM_FORMAT_MAX_PLANES];
    u8 char_per_block[DRM_FORMAT_MAX_PLANES];
  };
  u8 block_w[DRM_FORMAT_MAX_PLANES];
  u8 block_h[DRM_FORMAT_MAX_PLANES];
  u8 hsub;
  u8 vsub;
  bool has_alpha;
  bool is_yuv;
  bool is_color_indexed;
};

Members

format

4CC format identifier (DRM_FORMAT_*)

depth

Color depth (number of bits per pixel excluding padding bits), valid for a subset of RGB formats only. This is a legacy field, do not use in new code and set to 0 for new formats.

num_planes

Number of color planes (1 to 3)

{unnamed_union}

anonymous

cpp

Number of bytes per pixel (per plane), this is aliased with char_per_block. It is deprecated in favour of using the triplet char_per_block, block_w, block_h for better describing the pixel format.

char_per_block

Number of bytes per block (per plane), where blocks are defined as a rectangle of pixels which are stored next to each other in a byte aligned memory region. Together with block_w and block_h this is used to properly describe tiles in tiled formats or to describe groups of pixels in packed formats for which the memory needed for a single pixel is not byte aligned.

cpp has been kept for historical reasons because there are a lot of places in drivers where it’s used. In drm core for generic code paths the preferred way is to use char_per_block, drm_format_info_block_width() and drm_format_info_block_height() which allows handling both block and non-block formats in the same way.

For formats that are intended to be used only with non-linear modifiers both cpp and char_per_block must be 0 in the generic format table. Drivers could supply accurate information from their drm_mode_config.get_format_info hook if they want the core to be validating the pitch.

block_w

Block width in pixels, this is intended to be accessed through drm_format_info_block_width()

block_h

Block height in pixels, this is intended to be accessed through drm_format_info_block_height()

hsub

Horizontal chroma subsampling factor

vsub

Vertical chroma subsampling factor

has_alpha

Does the format embeds an alpha component?

is_yuv

Is it a YUV format?

is_color_indexed

Is it a color-indexed format?

bool drm_format_info_is_yuv_packed(const struct drm_format_info *info)¶: check that the format info matches a YUV format with data laid in a single plane

Parameters

const struct drm_format_info *info: format info

Return

A boolean indicating whether the format info matches a packed YUV format.

bool drm_format_info_is_yuv_semiplanar(const struct drm_format_info *info)¶: check that the format info matches a YUV format with data laid in two planes (luminance and chrominance)

Parameters

const struct drm_format_info *info: format info

Return

A boolean indicating whether the format info matches a semiplanar YUV format.

bool drm_format_info_is_yuv_planar(const struct drm_format_info *info)¶: check that the format info matches a YUV format with data laid in three planes (one for each YUV component)

Parameters

const struct drm_format_info *info: format info

Return

A boolean indicating whether the format info matches a planar YUV format.

bool drm_format_info_is_yuv_sampling_410(const struct drm_format_info *info)¶: check that the format info matches a YUV format with 4:1:0 sub-sampling

Parameters

const struct drm_format_info *info: format info

Return

A boolean indicating whether the format info matches a YUV format with 4:1:0 sub-sampling.

bool drm_format_info_is_yuv_sampling_411(const struct drm_format_info *info)¶: check that the format info matches a YUV format with 4:1:1 sub-sampling

Parameters

const struct drm_format_info *info: format info

Return

A boolean indicating whether the format info matches a YUV format with 4:1:1 sub-sampling.

bool drm_format_info_is_yuv_sampling_420(const struct drm_format_info *info)¶: check that the format info matches a YUV format with 4:2:0 sub-sampling

Parameters

const struct drm_format_info *info: format info

Return

A boolean indicating whether the format info matches a YUV format with 4:2:0 sub-sampling.

bool drm_format_info_is_yuv_sampling_422(const struct drm_format_info *info)¶: check that the format info matches a YUV format with 4:2:2 sub-sampling

Parameters

const struct drm_format_info *info: format info

Return

A boolean indicating whether the format info matches a YUV format with 4:2:2 sub-sampling.

bool drm_format_info_is_yuv_sampling_444(const struct drm_format_info *info)¶: check that the format info matches a YUV format with 4:4:4 sub-sampling

Parameters

const struct drm_format_info *info: format info

Return

A boolean indicating whether the format info matches a YUV format with 4:4:4 sub-sampling.

int drm_format_info_plane_width(const struct drm_format_info *info, int width, int plane)¶: width of the plane given the first plane

Parameters

const struct drm_format_info *info: pixel format info
int width: width of the first plane
int plane: plane index

Return

The width of plane, given that the width of the first plane is width.

int drm_format_info_plane_height(const struct drm_format_info *info, int height, int plane)¶: height of the plane given the first plane

Parameters

const struct drm_format_info *info: pixel format info
int height: height of the first plane
int plane: plane index

Return

The height of plane, given that the height of the first plane is height.

uint32_t drm_mode_legacy_fb_format(uint32_t bpp, uint32_t depth)¶: compute drm fourcc code from legacy description

Parameters

uint32_t bpp: bits per pixels
uint32_t depth: bit depth per pixel

Description

Computes a drm fourcc pixel format code for the given bpp/depth values. Useful in fbdev emulation code, since that deals in those values.

uint32_t drm_driver_legacy_fb_format(struct drm_device *dev, uint32_t bpp, uint32_t depth)¶: compute drm fourcc code from legacy description

Parameters

struct drm_device *dev: DRM device
uint32_t bpp: bits per pixels
uint32_t depth: bit depth per pixel

Description

Computes a drm fourcc pixel format code for the given bpp/depth values. Unlike drm_mode_legacy_fb_format() this looks at the drivers mode_config, and depending on the drm_mode_config.quirk_addfb_prefer_host_byte_order flag it returns little endian byte order or host byte order framebuffer formats.

const struct drm_format_info *drm_format_info(u32 format): query information for a given format

Parameters

u32 format: pixel format (DRM_FORMAT_*)

Description

The caller should only pass a supported pixel format to this function. Unsupported pixel formats will generate a warning in the kernel log.

Return

The instance of struct drm_format_info that describes the pixel format, or NULL if the format is unsupported.

const struct drm_format_info *drm_get_format_info(struct drm_device *dev, const struct drm_mode_fb_cmd2 *mode_cmd)¶: query information for a given framebuffer configuration

Parameters

struct drm_device *dev: DRM device
const struct drm_mode_fb_cmd2 *mode_cmd: metadata from the userspace fb creation request

Return

The instance of struct drm_format_info that describes the pixel format, or NULL if the format is unsupported.

unsigned int drm_format_info_block_width(const struct drm_format_info *info, int plane)¶: width in pixels of block.

Parameters

const struct drm_format_info *info: pixel format info
int plane: plane index

Return

The width in pixels of a block, depending on the plane index.

unsigned int drm_format_info_block_height(const struct drm_format_info *info, int plane)¶: height in pixels of a block

Parameters

const struct drm_format_info *info: pixel format info
int plane: plane index

Return

The height in pixels of a block, depending on the plane index.

unsigned int drm_format_info_bpp(const struct drm_format_info *info, int plane)¶: number of bits per pixel

Parameters

const struct drm_format_info *info: pixel format info
int plane: plane index

Return

The actual number of bits per pixel, depending on the plane index.

uint64_t drm_format_info_min_pitch(const struct drm_format_info *info, int plane, unsigned int buffer_width)¶: computes the minimum required pitch in bytes

Parameters

const struct drm_format_info *info: pixel format info
int plane: plane index
unsigned int buffer_width: buffer width in pixels

Return

The minimum required pitch in bytes for a buffer by taking into consideration the pixel format information and the buffer width.

Dumb Buffer Objects¶

The KMS API doesn’t standardize backing storage object creation and leaves it to driver-specific ioctls. Furthermore actually creating a buffer object even for GEM-based drivers is done through a driver-specific ioctl - GEM only has a common userspace interface for sharing and destroying objects. While not an issue for full-fledged graphics stacks that include device-specific userspace components (in libdrm for instance), this limit makes DRM-based early boot graphics unnecessarily complex.

Dumb objects partly alleviate the problem by providing a standard API to create dumb buffers suitable for scanout, which can then be used to create KMS frame buffers.

To support dumb objects drivers must implement the drm_driver.dumb_create and drm_driver.dumb_map_offset operations (the latter defaults to drm_gem_dumb_map_offset() if not set). Drivers that don’t use GEM handles additionally need to implement the drm_driver.dumb_destroy operation. See the callbacks for further details.

Note that dumb objects may not be used for gpu acceleration, as has been attempted on some ARM embedded platforms. Such drivers really must have a hardware-specific ioctl to allocate suitable buffer objects.

Plane Abstraction¶

A plane represents an image source that can be blended with or overlaid on top of a CRTC during the scanout process. Planes take their input data from a drm_framebuffer object. The plane itself specifies the cropping and scaling of that image, and where it is placed on the visible area of a display pipeline, represented by drm_crtc. A plane can also have additional properties that specify how the pixels are positioned and blended, like rotation or Z-position. All these properties are stored in drm_plane_state.

To create a plane, a KMS drivers allocates and zeroes an instances of struct drm_plane (possibly as part of a larger structure) and registers it with a call to drm_universal_plane_init().

Each plane has a type, see enum drm_plane_type. A plane can be compatible with multiple CRTCs, see drm_plane.possible_crtcs.

Each CRTC must have a unique primary plane userspace can attach to enable the CRTC. In other words, userspace must be able to attach a different primary plane to each CRTC at the same time. Primary planes can still be compatible with multiple CRTCs. There must be exactly as many primary planes as there are CRTCs.

Legacy uAPI doesn’t expose the primary and cursor planes directly. DRM core relies on the driver to set the primary and optionally the cursor plane used for legacy IOCTLs. This is done by calling drm_crtc_init_with_planes(). All drivers must provide one primary plane per CRTC to avoid surprising legacy userspace too much.

Plane Functions Reference¶

struct drm_plane_state¶: mutable plane state

Definition

struct drm_plane_state {
  struct drm_plane *plane;
  struct drm_crtc *crtc;
  struct drm_framebuffer *fb;
  struct dma_fence *fence;
  int32_t crtc_x;
  int32_t crtc_y;
  uint32_t crtc_w, crtc_h;
  uint32_t src_x;
  uint32_t src_y;
  uint32_t src_h, src_w;
  u16 alpha;
  uint16_t pixel_blend_mode;
  unsigned int rotation;
  unsigned int zpos;
  unsigned int normalized_zpos;
  enum drm_color_encoding color_encoding;
  enum drm_color_range color_range;
  struct drm_property_blob *fb_damage_clips;
  struct drm_rect src, dst;
  bool visible;
  enum drm_scaling_filter scaling_filter;
  struct drm_crtc_commit *commit;
  struct drm_atomic_state *state;
};

Members

plane

backpointer to the plane

crtc

Currently bound CRTC, NULL if disabled. Do not this write directly, use drm_atomic_set_crtc_for_plane()

fb

Currently bound framebuffer. Do not write this directly, use drm_atomic_set_fb_for_plane()

fence

Optional fence to wait for before scanning out fb. The core atomic code will set this when userspace is using explicit fencing. Do not write this field directly for a driver’s implicit fence.

Drivers should store any implicit fence in this from their drm_plane_helper_funcs.prepare_fb callback. See drm_gem_plane_helper_prepare_fb() and drm_gem_simple_display_pipe_prepare_fb() for suitable helpers.

crtc_x

Left position of visible portion of plane on crtc, signed dest location allows it to be partially off screen.

crtc_y

Upper position of visible portion of plane on crtc, signed dest location allows it to be partially off screen.

crtc_w

width of visible portion of plane on crtc

crtc_h

height of visible portion of plane on crtc

src_x

left position of visible portion of plane within plane (in 16.16 fixed point).

src_y

upper position of visible portion of plane within plane (in 16.16 fixed point).

src_h

height of visible portion of plane (in 16.16)

src_w

width of visible portion of plane (in 16.16)

alpha

Opacity of the plane with 0 as completely transparent and 0xffff as completely opaque. See drm_plane_create_alpha_property() for more details.

pixel_blend_mode

The alpha blending equation selection, describing how the pixels from the current plane are composited with the background. Value can be one of DRM_MODE_BLEND_*

rotation

Rotation of the plane. See drm_plane_create_rotation_property() for more details.

zpos

Priority of the given plane on crtc (optional).

User-space may set mutable zpos properties so that multiple active planes on the same CRTC have identical zpos values. This is a user-space bug, but drivers can solve the conflict by comparing the plane object IDs; the plane with a higher ID is stacked on top of a plane with a lower ID.

See drm_plane_create_zpos_property() and drm_plane_create_zpos_immutable_property() for more details.

normalized_zpos

Normalized value of zpos: unique, range from 0 to N-1 where N is the number of active planes for given crtc. Note that the driver must set drm_mode_config.normalize_zpos or call drm_atomic_normalize_zpos() to update this before it can be trusted.

color_encoding

Color encoding for non RGB formats

color_range

Color range for non RGB formats

fb_damage_clips

Blob representing damage (area in plane framebuffer that changed since last plane update) as an array of drm_mode_rect in framebuffer coodinates of the attached framebuffer. Note that unlike plane src, damage clips are not in 16.16 fixed point.

See drm_plane_get_damage_clips() and drm_plane_get_damage_clips_count() for accessing these.

src

source coordinates of the plane (in 16.16).

When using drm_atomic_helper_check_plane_state(), the coordinates are clipped, but the driver may choose to use unclipped coordinates instead when the hardware performs the clipping automatically.

dst

clipped destination coordinates of the plane.

When using drm_atomic_helper_check_plane_state(), the coordinates are clipped, but the driver may choose to use unclipped coordinates instead when the hardware performs the clipping automatically.

visible

Visibility of the plane. This can be false even if fb!=NULL and crtc!=NULL, due to clipping.

scaling_filter

Scaling filter to be applied

commit

Tracks the pending commit to prevent use-after-free conditions, and for async plane updates.

May be NULL.

state

backpointer to global drm_atomic_state

Description

Please note that the destination coordinates crtc_x, crtc_y, crtc_h and crtc_w and the source coordinates src_x, src_y, src_h and src_w are the raw coordinates provided by userspace. Drivers should use drm_atomic_helper_check_plane_state() and only use the derived rectangles in src and dst to program the hardware.

struct drm_plane_funcs¶: driver plane control functions

Definition

struct drm_plane_funcs {
  int (*update_plane)(struct drm_plane *plane,struct drm_crtc *crtc, struct drm_framebuffer *fb,int crtc_x, int crtc_y,unsigned int crtc_w, unsigned int crtc_h,uint32_t src_x, uint32_t src_y,uint32_t src_w, uint32_t src_h, struct drm_modeset_acquire_ctx *ctx);
  int (*disable_plane)(struct drm_plane *plane, struct drm_modeset_acquire_ctx *ctx);
  void (*destroy)(struct drm_plane *plane);
  void (*reset)(struct drm_plane *plane);
  int (*set_property)(struct drm_plane *plane, struct drm_property *property, uint64_t val);
  struct drm_plane_state *(*atomic_duplicate_state)(struct drm_plane *plane);
  void (*atomic_destroy_state)(struct drm_plane *plane, struct drm_plane_state *state);
  int (*atomic_set_property)(struct drm_plane *plane,struct drm_plane_state *state,struct drm_property *property, uint64_t val);
  int (*atomic_get_property)(struct drm_plane *plane,const struct drm_plane_state *state,struct drm_property *property, uint64_t *val);
  int (*late_register)(struct drm_plane *plane);
  void (*early_unregister)(struct drm_plane *plane);
  void (*atomic_print_state)(struct drm_printer *p, const struct drm_plane_state *state);
  bool (*format_mod_supported)(struct drm_plane *plane, uint32_t format, uint64_t modifier);
};

Members

update_plane

This is the legacy entry point to enable and configure the plane for the given CRTC and framebuffer. It is never called to disable the plane, i.e. the passed-in crtc and fb paramters are never NULL.

The source rectangle in frame buffer memory coordinates is given by the src_x, src_y, src_w and src_h parameters (as 16.16 fixed point values). Devices that don’t support subpixel plane coordinates can ignore the fractional part.

The destination rectangle in CRTC coordinates is given by the crtc_x, crtc_y, crtc_w and crtc_h parameters (as integer values). Devices scale the source rectangle to the destination rectangle. If scaling is not supported, and the source rectangle size doesn’t match the destination rectangle size, the driver must return a -<errorname>EINVAL</errorname> error.

Drivers implementing atomic modeset should use drm_atomic_helper_update_plane() to implement this hook.

RETURNS:

0 on success or a negative error code on failure.

disable_plane

This is the legacy entry point to disable the plane. The DRM core calls this method in response to a DRM_IOCTL_MODE_SETPLANE IOCTL call with the frame buffer ID set to 0. Disabled planes must not be processed by the CRTC.

Drivers implementing atomic modeset should use drm_atomic_helper_disable_plane() to implement this hook.

RETURNS:

0 on success or a negative error code on failure.

destroy

Clean up plane resources. This is only called at driver unload time through drm_mode_config_cleanup() since a plane cannot be hotplugged in DRM.

reset

Reset plane hardware and software state to off. This function isn’t called by the core directly, only through drm_mode_config_reset(). It’s not a helper hook only for historical reasons.

Atomic drivers can use drm_atomic_helper_plane_reset() to reset atomic state using this hook.

set_property

This is the legacy entry point to update a property attached to the plane.

This callback is optional if the driver does not support any legacy driver-private properties. For atomic drivers it is not used because property handling is done entirely in the DRM core.

RETURNS:

0 on success or a negative error code on failure.

atomic_duplicate_state

Duplicate the current atomic state for this plane and return it. The core and helpers guarantee that any atomic state duplicated with this hook and still owned by the caller (i.e. not transferred to the driver by calling drm_mode_config_funcs.atomic_commit) will be cleaned up by calling the atomic_destroy_state hook in this structure.

This callback is mandatory for atomic drivers.

Atomic drivers which don’t subclass struct drm_plane_state should use drm_atomic_helper_plane_duplicate_state(). Drivers that subclass the state structure to extend it with driver-private state should use __drm_atomic_helper_plane_duplicate_state() to make sure shared state is duplicated in a consistent fashion across drivers.

It is an error to call this hook before drm_plane.state has been initialized correctly.

NOTE:

If the duplicate state references refcounted resources this hook must acquire a reference for each of them. The driver must release these references again in atomic_destroy_state.

RETURNS:

Duplicated atomic state or NULL when the allocation failed.

atomic_destroy_state

Destroy a state duplicated with atomic_duplicate_state and release or unreference all resources it references

This callback is mandatory for atomic drivers.

atomic_set_property

Decode a driver-private property value and store the decoded value into the passed-in state structure. Since the atomic core decodes all standardized properties (even for extensions beyond the core set of properties which might not be implemented by all drivers) this requires drivers to subclass the state structure.

Such driver-private properties should really only be implemented for truly hardware/vendor specific state. Instead it is preferred to standardize atomic extension and decode the properties used to expose such an extension in the core.

Do not call this function directly, use drm_atomic_plane_set_property() instead.

This callback is optional if the driver does not support any driver-private atomic properties.

NOTE:

This function is called in the state assembly phase of atomic modesets, which can be aborted for any reason (including on userspace’s request to just check whether a configuration would be possible). Drivers MUST NOT touch any persistent state (hardware or software) or data structures except the passed in state parameter.

Also since userspace controls in which order properties are set this function must not do any input validation (since the state update is incomplete and hence likely inconsistent). Instead any such input validation must be done in the various atomic_check callbacks.

RETURNS:

0 if the property has been found, -EINVAL if the property isn’t implemented by the driver (which shouldn’t ever happen, the core only asks for properties attached to this plane). No other validation is allowed by the driver. The core already checks that the property value is within the range (integer, valid enum value, …) the driver set when registering the property.

atomic_get_property

Reads out the decoded driver-private property. This is used to implement the GETPLANE IOCTL.

Do not call this function directly, use drm_atomic_plane_get_property() instead.

This callback is optional if the driver does not support any driver-private atomic properties.

RETURNS:

0 on success, -EINVAL if the property isn’t implemented by the driver (which should never happen, the core only asks for properties attached to this plane).

late_register

This optional hook can be used to register additional userspace interfaces attached to the plane like debugfs interfaces. It is called late in the driver load sequence from drm_dev_register(). Everything added from this callback should be unregistered in the early_unregister callback.

Returns:

0 on success, or a negative error code on failure.

early_unregister

This optional hook should be used to unregister the additional userspace interfaces attached to the plane from late_register. It is called from drm_dev_unregister(), early in the driver unload sequence to disable userspace access before data structures are torndown.

atomic_print_state

If driver subclasses struct drm_plane_state, it should implement this optional hook for printing additional driver specific state.

Do not call this directly, use drm_atomic_plane_print_state() instead.

format_mod_supported

This optional hook is used for the DRM to determine if the given format/modifier combination is valid for the plane. This allows the DRM to generate the correct format bitmask (which formats apply to which modifier), and to validate modifiers at atomic_check time.

If not present, then any modifier in the plane’s modifier list is allowed with any of the plane’s formats.

Returns:

True if the given modifier is valid for that format on the plane. False otherwise.

enum drm_plane_type¶: uapi plane type enumeration

Constants

DRM_PLANE_TYPE_OVERLAY: Overlay planes represent all non-primary, non-cursor planes. Some drivers refer to these types of planes as “sprites” internally.
DRM_PLANE_TYPE_PRIMARY: A primary plane attached to a CRTC is the most likely to be able to light up the CRTC when no scaling/cropping is used and the plane covers the whole CRTC.
DRM_PLANE_TYPE_CURSOR: A cursor plane attached to a CRTC is more likely to be able to be enabled when no scaling/cropping is used and the framebuffer has the size indicated by drm_mode_config.cursor_width and drm_mode_config.cursor_height. Additionally, if the driver doesn’t support modifiers, the framebuffer should have a linear layout.

Description

For historical reasons not all planes are made the same. This enumeration is used to tell the different types of planes apart to implement the different uapi semantics for them. For userspace which is universal plane aware and which is using that atomic IOCTL there’s no difference between these planes (beyong what the driver and hardware can support of course).

For compatibility with legacy userspace, only overlay planes are made available to userspace by default. Userspace clients may set the DRM_CLIENT_CAP_UNIVERSAL_PLANES client capability bit to indicate that they wish to receive a universal plane list containing all plane types. See also drm_for_each_legacy_plane().

In addition to setting each plane’s type, drivers need to setup the drm_crtc.primary and optionally drm_crtc.cursor pointers for legacy IOCTLs. See drm_crtc_init_with_planes().

WARNING: The values of this enum is UABI since they’re exposed in the “type” property.

struct drm_plane¶: central DRM plane control structure

Definition

struct drm_plane {
  struct drm_device *dev;
  struct list_head head;
  char *name;
  struct drm_modeset_lock mutex;
  struct drm_mode_object base;
  uint32_t possible_crtcs;
  uint32_t *format_types;
  unsigned int format_count;
  bool format_default;
  uint64_t *modifiers;
  unsigned int modifier_count;
  struct drm_crtc *crtc;
  struct drm_framebuffer *fb;
  struct drm_framebuffer *old_fb;
  const struct drm_plane_funcs *funcs;
  struct drm_object_properties properties;
  enum drm_plane_type type;
  unsigned index;
  const struct drm_plane_helper_funcs *helper_private;
  struct drm_plane_state *state;
  struct drm_property *alpha_property;
  struct drm_property *zpos_property;
  struct drm_property *rotation_property;
  struct drm_property *blend_mode_property;
  struct drm_property *color_encoding_property;
  struct drm_property *color_range_property;
  struct drm_property *scaling_filter_property;
};

Members

dev

DRM device this plane belongs to

head

List of all planes on dev, linked from drm_mode_config.plane_list. Invariant over the lifetime of dev and therefore does not need locking.

name

human readable name, can be overwritten by the driver

mutex

Protects modeset plane state, together with the drm_crtc.mutex of CRTC this plane is linked to (when active, getting activated or getting disabled).

For atomic drivers specifically this protects state.

base

base mode object

possible_crtcs

pipes this plane can be bound to constructed from drm_crtc_mask()

format_types

array of formats supported by this plane

format_count

Size of the array pointed at by format_types.

format_default

driver hasn’t supplied supported formats for the plane. Used by the non-atomic driver compatibility wrapper only.

modifiers

array of modifiers supported by this plane

modifier_count

Size of the array pointed at by modifier_count.

crtc

Currently bound CRTC, only meaningful for non-atomic drivers. For atomic drivers this is forced to be NULL, atomic drivers should instead check drm_plane_state.crtc.

fb

Currently bound framebuffer, only meaningful for non-atomic drivers. For atomic drivers this is forced to be NULL, atomic drivers should instead check drm_plane_state.fb.

old_fb

Temporary tracking of the old fb while a modeset is ongoing. Only used by non-atomic drivers, forced to be NULL for atomic drivers.

funcs

plane control functions

properties

property tracking for this plane

type

Type of plane, see enum drm_plane_type for details.

index

Position inside the mode_config.list, can be used as an array index. It is invariant over the lifetime of the plane.

helper_private

mid-layer private data

state

Current atomic state for this plane.

This is protected by mutex. Note that nonblocking atomic commits access the current plane state without taking locks. Either by going through the struct drm_atomic_state pointers, see for_each_oldnew_plane_in_state(), for_each_old_plane_in_state() and for_each_new_plane_in_state(). Or through careful ordering of atomic commit operations as implemented in the atomic helpers, see struct drm_crtc_commit.

alpha_property

Optional alpha property for this plane. See drm_plane_create_alpha_property().

zpos_property

Optional zpos property for this plane. See drm_plane_create_zpos_property().

rotation_property

Optional rotation property for this plane. See drm_plane_create_rotation_property().

blend_mode_property

Optional “pixel blend mode” enum property for this plane. Blend mode property represents the alpha blending equation selection, describing how the pixels from the current plane are composited with the background.

color_encoding_property

Optional “COLOR_ENCODING” enum property for specifying color encoding for non RGB formats. See drm_plane_create_color_properties().

color_range_property

Optional “COLOR_RANGE” enum property for specifying color range for non RGB formats. See drm_plane_create_color_properties().

scaling_filter_property

property to apply a particular filter while scaling.

Description

Planes represent the scanout hardware of a display block. They receive their input data from a drm_framebuffer and feed it to a drm_crtc. Planes control the color conversion, see Plane Composition Properties for more details, and are also involved in the color conversion of input pixels, see Color Management Properties for details on that.

drmm_universal_plane_alloc¶

drmm_universal_plane_alloc (dev, type, member, possible_crtcs, funcs, formats, format_count, format_modifiers, plane_type, name, ...)

Allocate and initialize an universal plane object

Parameters

dev: DRM device
type: the type of the struct which contains struct drm_plane
member: the name of the drm_plane within type
possible_crtcs: bitmask of possible CRTCs
funcs: callbacks for the new plane
formats: array of supported formats (DRM_FORMAT_*)
format_count: number of elements in formats
format_modifiers: array of struct drm_format modifiers terminated by DRM_FORMAT_MOD_INVALID
plane_type: type of plane (overlay, primary, cursor)
name: printf style format string for the plane name, or NULL for default name
...: variable arguments

Description

Allocates and initializes a plane object of type type. Cleanup is automatically handled through registering drm_plane_cleanup() with drmm_add_action().

The drm_plane_funcs.destroy hook must be NULL.

Drivers that only support the DRM_FORMAT_MOD_LINEAR modifier support may set format_modifiers to NULL. The plane will advertise the linear modifier.

Return

Pointer to new plane, or ERR_PTR on failure.

drm_universal_plane_alloc¶

drm_universal_plane_alloc (dev, type, member, possible_crtcs, funcs, formats, format_count, format_modifiers, plane_type, name, ...)

Allocate and initialize an universal plane object

Parameters

dev: DRM device
type: the type of the struct which contains struct drm_plane
member: the name of the drm_plane within type
possible_crtcs: bitmask of possible CRTCs
funcs: callbacks for the new plane
formats: array of supported formats (DRM_FORMAT_*)
format_count: number of elements in formats
format_modifiers: array of struct drm_format modifiers terminated by DRM_FORMAT_MOD_INVALID
plane_type: type of plane (overlay, primary, cursor)
name: printf style format string for the plane name, or NULL for default name
...: variable arguments

Description

Allocates and initializes a plane object of type type. The caller is responsible for releasing the allocated memory with kfree().

Drivers are encouraged to use drmm_universal_plane_alloc() instead.

Drivers that only support the DRM_FORMAT_MOD_LINEAR modifier support may set format_modifiers to NULL. The plane will advertise the linear modifier.

Return

Pointer to new plane, or ERR_PTR on failure.

unsigned int drm_plane_index(const struct drm_plane *plane)¶: find the index of a registered plane

Parameters

const struct drm_plane *plane: plane to find index for

Description

Given a registered plane, return the index of that plane within a DRM device’s list of planes.

u32 drm_plane_mask(const struct drm_plane *plane)¶: find the mask of a registered plane

Parameters

const struct drm_plane *plane: plane to find mask for

struct drm_plane *drm_plane_find(struct drm_device *dev, struct drm_file *file_priv, uint32_t id)¶: find a drm_plane

Parameters

struct drm_device *dev: DRM device
struct drm_file *file_priv: drm file to check for lease against.
uint32_t id: plane id

Description

Returns the plane with id, NULL if it doesn’t exist. Simple wrapper around drm_mode_object_find().

drm_for_each_plane_mask¶

drm_for_each_plane_mask (plane, dev, plane_mask)

iterate over planes specified by bitmask

Parameters

plane: the loop cursor
dev: the DRM device
plane_mask: bitmask of plane indices

Description

Iterate over all planes specified by bitmask.

drm_for_each_legacy_plane¶

drm_for_each_legacy_plane (plane, dev)

iterate over all planes for legacy userspace

Parameters

plane: the loop cursor
dev: the DRM device

Description

Iterate over all legacy planes of dev, excluding primary and cursor planes. This is useful for implementing userspace apis when userspace is not universal plane aware. See also enum drm_plane_type.

drm_for_each_plane¶

drm_for_each_plane (plane, dev)

iterate over all planes

Parameters

plane: the loop cursor
dev: the DRM device

Description

Iterate over all planes of dev, include primary and cursor planes.

int drm_universal_plane_init(struct drm_device *dev, struct drm_plane *plane, uint32_t possible_crtcs, const struct drm_plane_funcs *funcs, const uint32_t *formats, unsigned int format_count, const uint64_t *format_modifiers, enum drm_plane_type type, const char *name, ...)¶: Initialize a new universal plane object

Parameters

struct drm_device *dev: DRM device
struct drm_plane *plane: plane object to init
uint32_t possible_crtcs: bitmask of possible CRTCs
const struct drm_plane_funcs *funcs: callbacks for the new plane
const uint32_t *formats: array of supported formats (DRM_FORMAT_*)
unsigned int format_count: number of elements in formats
const uint64_t *format_modifiers: array of struct drm_format modifiers terminated by DRM_FORMAT_MOD_INVALID
enum drm_plane_type type: type of plane (overlay, primary, cursor)
const char *name: printf style format string for the plane name, or NULL for default name
...: variable arguments

Description

Initializes a plane object of type type. The drm_plane_funcs.destroy hook should call drm_plane_cleanup() and kfree() the plane structure. The plane structure should not be allocated with devm_kzalloc().

Drivers that only support the DRM_FORMAT_MOD_LINEAR modifier support may set format_modifiers to NULL. The plane will advertise the linear modifier.

Note

consider using drmm_universal_plane_alloc() instead of drm_universal_plane_init() to let the DRM managed resource infrastructure take care of cleanup and deallocation.

Return

Zero on success, error code on failure.

void drm_plane_cleanup(struct drm_plane *plane)¶: Clean up the core plane usage

Parameters

struct drm_plane *plane: plane to cleanup

Description

This function cleans up plane and removes it from the DRM mode setting core. Note that the function does not free the plane structure itself, this is the responsibility of the caller.

struct drm_plane *drm_plane_from_index(struct drm_device *dev, int idx)¶: find the registered plane at an index

Parameters

struct drm_device *dev: DRM device
int idx: index of registered plane to find for

Description

Given a plane index, return the registered plane from DRM device’s list of planes with matching index. This is the inverse of drm_plane_index().

void drm_plane_force_disable(struct drm_plane *plane)¶: Forcibly disable a plane

Parameters

struct drm_plane *plane: plane to disable

Description

Forces the plane to be disabled.

Used when the plane’s current framebuffer is destroyed, and when restoring fbdev mode.

Note that this function is not suitable for atomic drivers, since it doesn’t wire through the lock acquisition context properly and hence can’t handle retries or driver private locks. You probably want to use drm_atomic_helper_disable_plane() or drm_atomic_helper_disable_planes_on_crtc() instead.

int drm_mode_plane_set_obj_prop(struct drm_plane *plane, struct drm_property *property, uint64_t value)¶: set the value of a property

Parameters

struct drm_plane *plane: drm plane object to set property value for
struct drm_property *property: property to set
uint64_t value: value the property should be set to

Description

This functions sets a given property on a given plane object. This function calls the driver’s ->set_property callback and changes the software state of the property if the callback succeeds.

Return

Zero on success, error code on failure.

bool drm_any_plane_has_format(struct drm_device *dev, u32 format, u64 modifier)¶: Check whether any plane supports this format and modifier combination

Parameters

struct drm_device *dev: DRM device
u32 format: pixel format (DRM_FORMAT_*)
u64 modifier: data layout modifier

Return

Whether at least one plane supports the specified format and modifier combination.

void drm_plane_enable_fb_damage_clips(struct drm_plane *plane)¶: Enables plane fb damage clips property.

Parameters

struct drm_plane *plane: Plane on which to enable damage clips property.

Description

This function lets driver to enable the damage clips property on a plane.

unsigned int drm_plane_get_damage_clips_count(const struct drm_plane_state *state)¶: Returns damage clips count.

Parameters

const struct drm_plane_state *state: Plane state.

Description

Simple helper to get the number of drm_mode_rect clips set by user-space during plane update.

Return

Number of clips in plane fb_damage_clips blob property.

struct drm_mode_rect *drm_plane_get_damage_clips(const struct drm_plane_state *state)¶: Returns damage clips.

Parameters

const struct drm_plane_state *state: Plane state.

Description

Note that this function returns uapi type drm_mode_rect. Drivers might want to use the helper functions drm_atomic_helper_damage_iter_init() and drm_atomic_helper_damage_iter_next() or drm_atomic_helper_damage_merged() if the driver can only handle a single damage region at most.

Return

Damage clips in plane fb_damage_clips blob property.

int drm_plane_create_scaling_filter_property(struct drm_plane *plane, unsigned int supported_filters)¶: create a new scaling filter property

Parameters

struct drm_plane *plane: drm plane
unsigned int supported_filters: bitmask of supported scaling filters, must include BIT(DRM_SCALING_FILTER_DEFAULT).

Description

This function lets driver to enable the scaling filter property on a given plane.

Return

Zero for success or -errno

Plane Composition Functions Reference¶

int drm_plane_create_alpha_property(struct drm_plane *plane)¶: create a new alpha property

Parameters

struct drm_plane *plane: drm plane

Description

This function creates a generic, mutable, alpha property and enables support for it in the DRM core. It is attached to plane.

The alpha property will be allowed to be within the bounds of 0 (transparent) to 0xffff (opaque).

Return

0 on success, negative error code on failure.

int drm_plane_create_rotation_property(struct drm_plane *plane, unsigned int rotation, unsigned int supported_rotations)¶: create a new rotation property

Parameters

struct drm_plane *plane: drm plane
unsigned int rotation: initial value of the rotation property
unsigned int supported_rotations: bitmask of supported rotations and reflections

Description

This creates a new property with the selected support for transformations.

Since a rotation by 180° degress is the same as reflecting both along the x and the y axis the rotation property is somewhat redundant. Drivers can use drm_rotation_simplify() to normalize values of this property.

The property exposed to userspace is a bitmask property (see drm_property_create_bitmask()) called “rotation” and has the following bitmask enumaration values:

DRM_MODE_ROTATE_0:: “rotate-0”
DRM_MODE_ROTATE_90:: “rotate-90”
DRM_MODE_ROTATE_180:: “rotate-180”
DRM_MODE_ROTATE_270:: “rotate-270”
DRM_MODE_REFLECT_X:: “reflect-x”
DRM_MODE_REFLECT_Y:: “reflect-y”

Rotation is the specified amount in degrees in counter clockwise direction, the X and Y axis are within the source rectangle, i.e. the X/Y axis before rotation. After reflection, the rotation is applied to the image sampled from the source rectangle, before scaling it to fit the destination rectangle.

unsigned int drm_rotation_simplify(unsigned int rotation, unsigned int supported_rotations)¶: Try to simplify the rotation

Parameters

unsigned int rotation: Rotation to be simplified
unsigned int supported_rotations: Supported rotations

Description

Attempt to simplify the rotation to a form that is supported. Eg. if the hardware supports everything except DRM_MODE_REFLECT_X one could call this function like this:

drm_rotation_simplify(rotation, DRM_MODE_ROTATE_0 |: DRM_MODE_ROTATE_90 | DRM_MODE_ROTATE_180 | DRM_MODE_ROTATE_270 | DRM_MODE_REFLECT_Y);

to eliminate the DRM_MODE_REFLECT_X flag. Depending on what kind of transforms the hardware supports, this function may not be able to produce a supported transform, so the caller should check the result afterwards.

int drm_plane_create_zpos_property(struct drm_plane *plane, unsigned int zpos, unsigned int min, unsigned int max)¶: create mutable zpos property

Parameters

struct drm_plane *plane: drm plane
unsigned int zpos: initial value of zpos property
unsigned int min: minimal possible value of zpos property
unsigned int max: maximal possible value of zpos property

Description

This function initializes generic mutable zpos property and enables support for it in drm core. Drivers can then attach this property to planes to enable support for configurable planes arrangement during blending operation. Drivers that attach a mutable zpos property to any plane should call the drm_atomic_normalize_zpos() helper during their implementation of drm_mode_config_funcs.atomic_check(), which will update the normalized zpos values and store them in drm_plane_state.normalized_zpos. Usually min should be set to 0 and max to maximal number of planes for given crtc - 1.

If zpos of some planes cannot be changed (like fixed background or cursor/topmost planes), drivers shall adjust the min/max values and assign those planes immutable zpos properties with lower or higher values (for more information, see drm_plane_create_zpos_immutable_property() function). In such case drivers shall also assign proper initial zpos values for all planes in its plane_reset() callback, so the planes will be always sorted properly.

Plane Damage Tracking Functions Reference¶

void drm_atomic_helper_check_plane_damage(struct drm_atomic_state *state, struct drm_plane_state *plane_state)¶: Verify plane damage on atomic_check.

Parameters

struct drm_atomic_state *state: The driver state object.
struct drm_plane_state *plane_state: Plane state for which to verify damage.

Description

This helper function makes sure that damage from plane state is discarded for full modeset. If there are more reasons a driver would want to do a full plane update rather than processing individual damage regions, then those cases should be taken care of here.

Note that drm_plane_state.fb_damage_clips == NULL in plane state means that full plane update should happen. It also ensure helper iterator will return drm_plane_state.src as damage.

int drm_atomic_helper_dirtyfb(struct drm_framebuffer *fb, struct drm_file *file_priv, unsigned int flags, unsigned int color, struct drm_clip_rect *clips, unsigned int num_clips)¶: Helper for dirtyfb.

Parameters

struct drm_framebuffer *fb: DRM framebuffer.
struct drm_file *file_priv: Drm file for the ioctl call.
unsigned int flags: Dirty fb annotate flags.
unsigned int color: Color for annotate fill.
struct drm_clip_rect *clips: Dirty region.
unsigned int num_clips: Count of clip in clips.

Description

A helper to implement drm_framebuffer_funcs.dirty using damage interface during plane update. If num_clips is 0 then this helper will do a full plane update. This is the same behaviour expected by DIRTFB IOCTL.

Note that this helper is blocking implementation. This is what current drivers and userspace expect in their DIRTYFB IOCTL implementation, as a way to rate-limit userspace and make sure its rendering doesn’t get ahead of uploading new data too much.

Return

Zero on success, negative errno on failure.

void drm_atomic_helper_damage_iter_init(struct drm_atomic_helper_damage_iter *iter, const struct drm_plane_state *old_state, const struct drm_plane_state *state)¶: Initialize the damage iterator.

Parameters

struct drm_atomic_helper_damage_iter *iter: The iterator to initialize.
const struct drm_plane_state *old_state: Old plane state for validation.
const struct drm_plane_state *state: Plane state from which to iterate the damage clips.

Description

Initialize an iterator, which clips plane damage drm_plane_state.fb_damage_clips to plane drm_plane_state.src. This iterator returns full plane src in case damage is not present because either user-space didn’t sent or driver discarded it (it want to do full plane update). Currently this iterator returns full plane src in case plane src changed but that can be changed in future to return damage.

For the case when plane is not visible or plane update should not happen the first call to iter_next will return false. Note that this helper use clipped drm_plane_state.src, so driver calling this helper should have called drm_atomic_helper_check_plane_state() earlier.

bool drm_atomic_helper_damage_iter_next(struct drm_atomic_helper_damage_iter *iter, struct drm_rect *rect)¶: Advance the damage iterator.

Parameters

struct drm_atomic_helper_damage_iter *iter: The iterator to advance.
struct drm_rect *rect: Return a rectangle in fb coordinate clipped to plane src.

Description

Since plane src is in 16.16 fixed point and damage clips are whole number, this iterator round off clips that intersect with plane src. Round down for x1/y1 and round up for x2/y2 for the intersected coordinate. Similar rounding off for full plane src, in case it’s returned as damage. This iterator will skip damage clips outside of plane src.

If the first call to iterator next returns false then it means no need to update the plane.

Return

True if the output is valid, false if reached the end.

bool drm_atomic_helper_damage_merged(const struct drm_plane_state *old_state, struct drm_plane_state *state, struct drm_rect *rect)¶: Merged plane damage

Parameters

const struct drm_plane_state *old_state: Old plane state for validation.
struct drm_plane_state *state: Plane state from which to iterate the damage clips.
struct drm_rect *rect: Returns the merged damage rectangle

Description

This function merges any valid plane damage clips into one rectangle and returns it in rect.

For details see: drm_atomic_helper_damage_iter_init() and drm_atomic_helper_damage_iter_next().

Return

True if there is valid plane damage otherwise false.

drm_atomic_for_each_plane_damage¶

drm_atomic_for_each_plane_damage (iter, rect)

Iterator macro for plane damage.

Parameters

iter: The iterator to advance.
rect: Return a rectangle in fb coordinate clipped to plane src.

Description

Note that if the first call to iterator macro return false then no need to do plane update. Iterator will return full plane src when damage is not passed by user-space.

struct drm_atomic_helper_damage_iter¶: Closure structure for damage iterator.

Definition

struct drm_atomic_helper_damage_iter {
};

Members

Description

This structure tracks state needed to walk the list of plane damage clips.

Display Modes Function Reference¶

enum drm_mode_status¶: hardware support status of a mode

Constants

MODE_OK: Mode OK
MODE_HSYNC: hsync out of range
MODE_VSYNC: vsync out of range
MODE_H_ILLEGAL: mode has illegal horizontal timings
MODE_V_ILLEGAL: mode has illegal vertical timings
MODE_BAD_WIDTH: requires an unsupported linepitch
MODE_NOMODE: no mode with a matching name
MODE_NO_INTERLACE: interlaced mode not supported
MODE_NO_DBLESCAN: doublescan mode not supported
MODE_NO_VSCAN: multiscan mode not supported
MODE_MEM: insufficient video memory
MODE_VIRTUAL_X: mode width too large for specified virtual size
MODE_VIRTUAL_Y: mode height too large for specified virtual size
MODE_MEM_VIRT: insufficient video memory given virtual size
MODE_NOCLOCK: no fixed clock available
MODE_CLOCK_HIGH: clock required is too high
MODE_CLOCK_LOW: clock required is too low
MODE_CLOCK_RANGE: clock/mode isn’t in a ClockRange
MODE_BAD_HVALUE: horizontal timing was out of range
MODE_BAD_VVALUE: vertical timing was out of range
MODE_BAD_VSCAN: VScan value out of range
MODE_HSYNC_NARROW: horizontal sync too narrow
MODE_HSYNC_WIDE: horizontal sync too wide
MODE_HBLANK_NARROW: horizontal blanking too narrow
MODE_HBLANK_WIDE: horizontal blanking too wide
MODE_VSYNC_NARROW: vertical sync too narrow
MODE_VSYNC_WIDE: vertical sync too wide
MODE_VBLANK_NARROW: vertical blanking too narrow
MODE_VBLANK_WIDE: vertical blanking too wide
MODE_PANEL: exceeds panel dimensions
MODE_INTERLACE_WIDTH: width too large for interlaced mode
MODE_ONE_WIDTH: only one width is supported
MODE_ONE_HEIGHT: only one height is supported
MODE_ONE_SIZE: only one resolution is supported
MODE_NO_REDUCED: monitor doesn’t accept reduced blanking
MODE_NO_STEREO: stereo modes not supported
MODE_NO_420: ycbcr 420 modes not supported
MODE_STALE: mode has become stale
MODE_BAD: unspecified reason
MODE_ERROR: error condition

Description

This enum is used to filter out modes not supported by the driver/hardware combination.

DRM_MODE_RES_MM¶

DRM_MODE_RES_MM (res, dpi)

Calculates the display size from resolution and DPI

Parameters

res: The resolution in pixel
dpi: The number of dots per inch

DRM_MODE_INIT¶

DRM_MODE_INIT (hz, hd, vd, hd_mm, vd_mm)

Initialize display mode

Parameters

hz: Vertical refresh rate in Hertz
hd: Horizontal resolution, width
vd: Vertical resolution, height
hd_mm: Display width in millimeters
vd_mm: Display height in millimeters

Description

This macro initializes a drm_display_mode that contains information about refresh rate, resolution and physical size.

DRM_SIMPLE_MODE¶

DRM_SIMPLE_MODE (hd, vd, hd_mm, vd_mm)

Simple display mode

Parameters

hd: Horizontal resolution, width
vd: Vertical resolution, height
hd_mm: Display width in millimeters
vd_mm: Display height in millimeters

Description

This macro initializes a drm_display_mode that only contains info about resolution and physical size.

struct drm_display_mode¶: DRM kernel-internal display mode structure

Definition

struct drm_display_mode {
  int clock;
  u16 hdisplay;
  u16 hsync_start;
  u16 hsync_end;
  u16 htotal;
  u16 hskew;
  u16 vdisplay;
  u16 vsync_start;
  u16 vsync_end;
  u16 vtotal;
  u16 vscan;
  u32 flags;
  int crtc_clock;
  u16 crtc_hdisplay;
  u16 crtc_hblank_start;
  u16 crtc_hblank_end;
  u16 crtc_hsync_start;
  u16 crtc_hsync_end;
  u16 crtc_htotal;
  u16 crtc_hskew;
  u16 crtc_vdisplay;
  u16 crtc_vblank_start;
  u16 crtc_vblank_end;
  u16 crtc_vsync_start;
  u16 crtc_vsync_end;
  u16 crtc_vtotal;
  u16 width_mm;
  u16 height_mm;
  u8 type;
  bool expose_to_userspace;
  struct list_head head;
  char name[DRM_DISPLAY_MODE_LEN];
  enum drm_mode_status status;
  enum hdmi_picture_aspect picture_aspect_ratio;
};

Members

clock

Pixel clock in kHz.

hdisplay

horizontal display size

hsync_start

horizontal sync start

hsync_end

horizontal sync end

htotal

horizontal total size

hskew

horizontal skew?!

vdisplay

vertical display size

vsync_start

vertical sync start

vsync_end

vertical sync end

vtotal

vertical total size

vscan

vertical scan?!

flags

Sync and timing flags:

DRM_MODE_FLAG_PHSYNC: horizontal sync is active high.

DRM_MODE_FLAG_NHSYNC: horizontal sync is active low.

DRM_MODE_FLAG_PVSYNC: vertical sync is active high.

DRM_MODE_FLAG_NVSYNC: vertical sync is active low.

DRM_MODE_FLAG_INTERLACE: mode is interlaced.

DRM_MODE_FLAG_DBLSCAN: mode uses doublescan.

DRM_MODE_FLAG_CSYNC: mode uses composite sync.

DRM_MODE_FLAG_PCSYNC: composite sync is active high.

DRM_MODE_FLAG_NCSYNC: composite sync is active low.

DRM_MODE_FLAG_HSKEW: hskew provided (not used?).

DRM_MODE_FLAG_BCAST: <deprecated>

DRM_MODE_FLAG_PIXMUX: <deprecated>

DRM_MODE_FLAG_DBLCLK: double-clocked mode.

DRM_MODE_FLAG_CLKDIV2: half-clocked mode.

Additionally there’s flags to specify how 3D modes are packed:

DRM_MODE_FLAG_3D_NONE: normal, non-3D mode.

DRM_MODE_FLAG_3D_FRAME_PACKING: 2 full frames for left and right.

DRM_MODE_FLAG_3D_FIELD_ALTERNATIVE: interleaved like fields.

DRM_MODE_FLAG_3D_LINE_ALTERNATIVE: interleaved lines.

DRM_MODE_FLAG_3D_SIDE_BY_SIDE_FULL: side-by-side full frames.

DRM_MODE_FLAG_3D_L_DEPTH: ?

DRM_MODE_FLAG_3D_L_DEPTH_GFX_GFX_DEPTH: ?

DRM_MODE_FLAG_3D_TOP_AND_BOTTOM: frame split into top and bottom parts.

DRM_MODE_FLAG_3D_SIDE_BY_SIDE_HALF: frame split into left and right parts.

crtc_clock

Actual pixel or dot clock in the hardware. This differs from the logical clock when e.g. using interlacing, double-clocking, stereo modes or other fancy stuff that changes the timings and signals actually sent over the wire.

This is again in kHz.

Note that with digital outputs like HDMI or DP there’s usually a massive confusion between the dot clock and the signal clock at the bit encoding level. Especially when a 8b/10b encoding is used and the difference is exactly a factor of 10.

crtc_hdisplay

hardware mode horizontal display size

crtc_hblank_start

hardware mode horizontal blank start

crtc_hblank_end

hardware mode horizontal blank end

crtc_hsync_start

hardware mode horizontal sync start

crtc_hsync_end

hardware mode horizontal sync end

crtc_htotal

hardware mode horizontal total size

crtc_hskew

hardware mode horizontal skew?!

crtc_vdisplay

hardware mode vertical display size

crtc_vblank_start

hardware mode vertical blank start

crtc_vblank_end

hardware mode vertical blank end

crtc_vsync_start

hardware mode vertical sync start

crtc_vsync_end

hardware mode vertical sync end

crtc_vtotal

hardware mode vertical total size

width_mm

Addressable size of the output in mm, projectors should set this to 0.

height_mm

Addressable size of the output in mm, projectors should set this to 0.

type

A bitmask of flags, mostly about the source of a mode. Possible flags are:

DRM_MODE_TYPE_PREFERRED: Preferred mode, usually the native resolution of an LCD panel. There should only be one preferred mode per connector at any given time.

DRM_MODE_TYPE_DRIVER: Mode created by the driver, which is all of them really. Drivers must set this bit for all modes they create and expose to userspace.

DRM_MODE_TYPE_USERDEF: Mode defined or selected via the kernel command line.

Plus a big list of flags which shouldn’t be used at all, but are still around since these flags are also used in the userspace ABI. We no longer accept modes with these types though:

DRM_MODE_TYPE_BUILTIN: Meant for hard-coded modes, unused. Use DRM_MODE_TYPE_DRIVER instead.

DRM_MODE_TYPE_DEFAULT: Again a leftover, use DRM_MODE_TYPE_PREFERRED instead.

DRM_MODE_TYPE_CLOCK_C and DRM_MODE_TYPE_CRTC_C: Define leftovers which are stuck around for hysterical raisins only. No one has an idea what they were meant for. Don’t use.

expose_to_userspace

Indicates whether the mode is to be exposed to the userspace. This is to maintain a set of exposed modes while preparing user-mode’s list in drm_mode_getconnector ioctl. The purpose of this only lies in the ioctl function, and is not to be used outside the function.

head

struct list_head for mode lists.

name

Human-readable name of the mode, filled out with drm_mode_set_name().

status

Status of the mode, used to filter out modes not supported by the hardware. See enum drm_mode_status.

picture_aspect_ratio

Field for setting the HDMI picture aspect ratio of a mode.

Description

This is the kernel API display mode information structure. For the user-space version see struct drm_mode_modeinfo.

The horizontal and vertical timings are defined per the following diagram.

          Active                 Front           Sync           Back
         Region                 Porch                          Porch
<-----------------------><----------------><-------------><-------------->
  //////////////////////|
 ////////////////////// |
//////////////////////  |..................               ................
                                           _______________
<----- [hv]display ----->
<------------- [hv]sync_start ------------>
<--------------------- [hv]sync_end --------------------->
<-------------------------------- [hv]total ----------------------------->*

This structure contains two copies of timings. First are the plain timings, which specify the logical mode, as it would be for a progressive 1:1 scanout at the refresh rate userspace can observe through vblank timestamps. Then there’s the hardware timings, which are corrected for interlacing, double-clocking and similar things. They are provided as a convenience, and can be appropriately computed using drm_mode_set_crtcinfo().

For printing you can use DRM_MODE_FMT and DRM_MODE_ARG().

DRM_MODE_FMT¶

DRM_MODE_FMT ()

printf string for struct drm_display_mode

Parameters

DRM_MODE_ARG¶

DRM_MODE_ARG (m)

printf arguments for struct drm_display_mode

Parameters

m: display mode

bool drm_mode_is_stereo(const struct drm_display_mode *mode)¶: check for stereo mode flags

Parameters

const struct drm_display_mode *mode: drm_display_mode to check

Return

True if the mode is one of the stereo modes (like side-by-side), false if not.

void drm_mode_debug_printmodeline(const struct drm_display_mode *mode)¶: print a mode to dmesg

Parameters

const struct drm_display_mode *mode: mode to print

Description

Describe mode using DRM_DEBUG.

struct drm_display_mode *drm_mode_create(struct drm_device *dev)¶: create a new display mode

Parameters

struct drm_device *dev: DRM device

Description

Create a new, cleared drm_display_mode with kzalloc, allocate an ID for it and return it.

Return

Pointer to new mode on success, NULL on error.

void drm_mode_destroy(struct drm_device *dev, struct drm_display_mode *mode)¶: remove a mode

Parameters

struct drm_device *dev: DRM device
struct drm_display_mode *mode: mode to remove

Description

Release mode’s unique ID, then free it mode structure itself using kfree.

void drm_mode_probed_add(struct drm_connector *connector, struct drm_display_mode *mode)¶: add a mode to a connector’s probed_mode list

Parameters

struct drm_connector *connector: connector the new mode
struct drm_display_mode *mode: mode data

Description

Add mode to connector’s probed_mode list for later use. This list should then in a second step get filtered and all the modes actually supported by the hardware moved to the connector’s modes list.

struct drm_display_mode *drm_cvt_mode(struct drm_device *dev, int hdisplay, int vdisplay, int vrefresh, bool reduced, bool interlaced, bool margins)¶: create a modeline based on the CVT algorithm

Parameters

struct drm_device *dev: drm device
int hdisplay: hdisplay size
int vdisplay: vdisplay size
int vrefresh: vrefresh rate
bool reduced: whether to use reduced blanking
bool interlaced: whether to compute an interlaced mode
bool margins: whether to add margins (borders)

Description

This function is called to generate the modeline based on CVT algorithm according to the hdisplay, vdisplay, vrefresh. It is based from the VESA(TM) Coordinated Video Timing Generator by Graham Loveridge April 9, 2003 available at http://www.elo.utfsm.cl/~elo212/docs/CVTd6r1.xls

And it is copied from xf86CVTmode in xserver/hw/xfree86/modes/xf86cvt.c. What I have done is to translate it by using integer calculation.

Return

The modeline based on the CVT algorithm stored in a drm_display_mode object. The display mode object is allocated with drm_mode_create(). Returns NULL when no mode could be allocated.

struct drm_display_mode *drm_gtf_mode_complex(struct drm_device *dev, int hdisplay, int vdisplay, int vrefresh, bool interlaced, int margins, int GTF_M, int GTF_2C, int GTF_K, int GTF_2J)¶: create the modeline based on the full GTF algorithm

Parameters

struct drm_device *dev: drm device
int hdisplay: hdisplay size
int vdisplay: vdisplay size
int vrefresh: vrefresh rate.
bool interlaced: whether to compute an interlaced mode
int margins: desired margin (borders) size
int GTF_M: extended GTF formula parameters
int GTF_2C: extended GTF formula parameters
int GTF_K: extended GTF formula parameters
int GTF_2J: extended GTF formula parameters

Description

GTF feature blocks specify C and J in multiples of 0.5, so we pass them in here multiplied by two. For a C of 40, pass in 80.

Return

The modeline based on the full GTF algorithm stored in a drm_display_mode object. The display mode object is allocated with drm_mode_create(). Returns NULL when no mode could be allocated.

struct drm_display_mode *drm_gtf_mode(struct drm_device *dev, int hdisplay, int vdisplay, int vrefresh, bool interlaced, int margins)¶: create the modeline based on the GTF algorithm

Parameters

struct drm_device *dev: drm device
int hdisplay: hdisplay size
int vdisplay: vdisplay size
int vrefresh: vrefresh rate.
bool interlaced: whether to compute an interlaced mode
int margins: desired margin (borders) size

Description

return the modeline based on GTF algorithm

This function is to create the modeline based on the GTF algorithm. Generalized Timing Formula is derived from:

GTF Spreadsheet by Andy Morrish (1/5/97) available at https://www.vesa.org

And it is copied from the file of xserver/hw/xfree86/modes/xf86gtf.c. What I have done is to translate it by using integer calculation. I also refer to the function of fb_get_mode in the file of drivers/video/fbmon.c

Standard GTF parameters:

M = 600
C = 40
K = 128
J = 20

Return

The modeline based on the GTF algorithm stored in a drm_display_mode object. The display mode object is allocated with drm_mode_create(). Returns NULL when no mode could be allocated.

void drm_display_mode_from_videomode(const struct videomode *vm, struct drm_display_mode *dmode)¶: fill in dmode using vm,

Parameters

const struct videomode *vm: videomode structure to use as source
struct drm_display_mode *dmode: drm_display_mode structure to use as destination

Description

Fills out dmode using the display mode specified in vm.

void drm_display_mode_to_videomode(const struct drm_display_mode *dmode, struct videomode *vm)¶: fill in vm using dmode,

Parameters

const struct drm_display_mode *dmode: drm_display_mode structure to use as source
struct videomode *vm: videomode structure to use as destination

Description

Fills out vm using the display mode specified in dmode.

void drm_bus_flags_from_videomode(const struct videomode *vm, u32 *bus_flags)¶: extract information about pixelclk and DE polarity from videomode and store it in a separate variable

Parameters

const struct videomode *vm: videomode structure to use
u32 *bus_flags: information about pixelclk, sync and DE polarity will be stored here

Description

Sets DRM_BUS_FLAG_DE_(LOW|HIGH), DRM_BUS_FLAG_PIXDATA_DRIVE_(POS|NEG)EDGE and DISPLAY_FLAGS_SYNC_(POS|NEG)EDGE in bus_flags according to DISPLAY_FLAGS found in vm

int of_get_drm_display_mode(struct device_node *np, struct drm_display_mode *dmode, u32 *bus_flags, int index)¶: get a drm_display_mode from devicetree

Parameters

struct device_node *np: device_node with the timing specification
struct drm_display_mode *dmode: will be set to the return value
u32 *bus_flags: information about pixelclk, sync and DE polarity
int index: index into the list of display timings in devicetree

Description

This function is expensive and should only be used, if only one mode is to be read from DT. To get multiple modes start with of_get_display_timings and work with that instead.

Return

0 on success, a negative errno code when no of videomode node was found.

int of_get_drm_panel_display_mode(struct device_node *np, struct drm_display_mode *dmode, u32 *bus_flags)¶: get a panel-timing drm_display_mode from devicetree

Parameters

struct device_node *np: device_node with the panel-timing specification
struct drm_display_mode *dmode: will be set to the return value
u32 *bus_flags: information about pixelclk, sync and DE polarity

Description

The mandatory Device Tree properties width-mm and height-mm are read and set on the display mode.

Return

Zero on success, negative error code on failure.

void drm_mode_set_name(struct drm_display_mode *mode)¶: set the name on a mode

Parameters

struct drm_display_mode *mode: name will be set in this mode

Description

Set the name of mode to a standard format which is <hdisplay>x<vdisplay> with an optional ‘i’ suffix for interlaced modes.

int drm_mode_vrefresh(const struct drm_display_mode *mode)¶: get the vrefresh of a mode

Parameters

const struct drm_display_mode *mode: mode

Return

modes’s vrefresh rate in Hz, rounded to the nearest integer. Calculates the value first if it is not yet set.

void drm_mode_get_hv_timing(const struct drm_display_mode *mode, int *hdisplay, int *vdisplay)¶: Fetches hdisplay/vdisplay for given mode

Parameters

const struct drm_display_mode *mode: mode to query
int *hdisplay: hdisplay value to fill in
int *vdisplay: vdisplay value to fill in

Description

The vdisplay value will be doubled if the specified mode is a stereo mode of the appropriate layout.

void drm_mode_set_crtcinfo(struct drm_display_mode *p, int adjust_flags)¶: set CRTC modesetting timing parameters

Parameters

struct drm_display_mode *p: mode
int adjust_flags: a combination of adjustment flags

Description

Setup the CRTC modesetting timing parameters for p, adjusting if necessary.

The CRTC_INTERLACE_HALVE_V flag can be used to halve vertical timings of interlaced modes.
The CRTC_STEREO_DOUBLE flag can be used to compute the timings for buffers containing two eyes (only adjust the timings when needed, eg. for “frame packing” or “side by side full”).
The CRTC_NO_DBLSCAN and CRTC_NO_VSCAN flags request that adjustment not be performed for doublescan and vscan > 1 modes respectively.

void drm_mode_copy(struct drm_display_mode *dst, const struct drm_display_mode *src)¶: copy the mode

Parameters

struct drm_display_mode *dst: mode to overwrite
const struct drm_display_mode *src: mode to copy

Description

Copy an existing mode into another mode, preserving the list head of the destination mode.

void drm_mode_init(struct drm_display_mode *dst, const struct drm_display_mode *src)¶: initialize the mode from another mode

Parameters

struct drm_display_mode *dst: mode to overwrite
const struct drm_display_mode *src: mode to copy

Description

Copy an existing mode into another mode, zeroing the list head of the destination mode. Typically used to guarantee the list head is not left with stack garbage in on-stack modes.

struct drm_display_mode *drm_mode_duplicate(struct drm_device *dev, const struct drm_display_mode *mode)¶: allocate and duplicate an existing mode

Parameters

struct drm_device *dev: drm_device to allocate the duplicated mode for
const struct drm_display_mode *mode: mode to duplicate

Description

Just allocate a new mode, copy the existing mode into it, and return a pointer to it. Used to create new instances of established modes.

Return

Pointer to duplicated mode on success, NULL on error.

bool drm_mode_match(const struct drm_display_mode *mode1, const struct drm_display_mode *mode2, unsigned int match_flags)¶: test modes for (partial) equality

Parameters

const struct drm_display_mode *mode1: first mode
const struct drm_display_mode *mode2: second mode
unsigned int match_flags: which parts need to match (DRM_MODE_MATCH_*)

Description

Check to see if mode1 and mode2 are equivalent.

Return

True if the modes are (partially) equal, false otherwise.

bool drm_mode_equal(const struct drm_display_mode *mode1, const struct drm_display_mode *mode2)¶: test modes for equality

Parameters

const struct drm_display_mode *mode1: first mode
const struct drm_display_mode *mode2: second mode

Description

Check to see if mode1 and mode2 are equivalent.

Return

True if the modes are equal, false otherwise.

bool drm_mode_equal_no_clocks(const struct drm_display_mode *mode1, const struct drm_display_mode *mode2)¶: test modes for equality

Parameters

const struct drm_display_mode *mode1: first mode
const struct drm_display_mode *mode2: second mode

Description

Check to see if mode1 and mode2 are equivalent, but don’t check the pixel clocks.

Return

True if the modes are equal, false otherwise.

bool drm_mode_equal_no_clocks_no_stereo(const struct drm_display_mode *mode1, const struct drm_display_mode *mode2)¶: test modes for equality

Parameters

const struct drm_display_mode *mode1: first mode
const struct drm_display_mode *mode2: second mode

Description

Check to see if mode1 and mode2 are equivalent, but don’t check the pixel clocks nor the stereo layout.

Return

True if the modes are equal, false otherwise.

enum drm_mode_status drm_mode_validate_driver(struct drm_device *dev, const struct drm_display_mode *mode)¶: make sure the mode is somewhat sane

Parameters

struct drm_device *dev: drm device
const struct drm_display_mode *mode: mode to check

Description

First do basic validation on the mode, and then allow the driver to check for device/driver specific limitations via the optional drm_mode_config_helper_funcs.mode_valid hook.

Return

The mode status

enum drm_mode_status drm_mode_validate_size(const struct drm_display_mode *mode, int maxX, int maxY)¶: make sure modes adhere to size constraints

Parameters

const struct drm_display_mode *mode: mode to check
int maxX: maximum width
int maxY: maximum height

Description

This function is a helper which can be used to validate modes against size limitations of the DRM device/connector. If a mode is too big its status member is updated with the appropriate validation failure code. The list itself is not changed.

Return

The mode status

enum drm_mode_status drm_mode_validate_ycbcr420(const struct drm_display_mode *mode, struct drm_connector *connector)¶: add ‘ycbcr420-only’ modes only when allowed

Parameters

const struct drm_display_mode *mode: mode to check
struct drm_connector *connector: drm connector under action

Description

This function is a helper which can be used to filter out any YCBCR420 only mode, when the source doesn’t support it.

Return

The mode status

void drm_mode_prune_invalid(struct drm_device *dev, struct list_head *mode_list, bool verbose)¶: remove invalid modes from mode list

Parameters

struct drm_device *dev: DRM device
struct list_head *mode_list: list of modes to check
bool verbose: be verbose about it

Description

This helper function can be used to prune a display mode list after validation has been completed. All modes whose status is not MODE_OK will be removed from the list, and if verbose the status code and mode name is also printed to dmesg.

void drm_mode_sort(struct list_head *mode_list)¶: sort mode list

Parameters

struct list_head *mode_list: list of drm_display_mode structures to sort

Description

Sort mode_list by favorability, moving good modes to the head of the list.

void drm_connector_list_update(struct drm_connector *connector)¶: update the mode list for the connector

Parameters

struct drm_connector *connector: the connector to update

Description

This moves the modes from the connector probed_modes list to the actual mode list. It compares the probed mode against the current list and only adds different/new modes.

This is just a helper functions doesn’t validate any modes itself and also doesn’t prune any invalid modes. Callers need to do that themselves.

bool drm_mode_parse_command_line_for_connector(const char *mode_option, const struct drm_connector *connector, struct drm_cmdline_mode *mode)¶: parse command line modeline for connector

Parameters

const char *mode_option: optional per connector mode option
const struct drm_connector *connector: connector to parse modeline for
struct drm_cmdline_mode *mode: preallocated drm_cmdline_mode structure to fill out

Description

This parses mode_option command line modeline for modes and options to configure the connector. If mode_option is NULL the default command line modeline in fb_mode_option will be parsed instead.

This uses the same parameters as the fb modedb.c, except for an extra force-enable, force-enable-digital and force-disable bit at the end:

<xres>x<yres>[M][R][-<bpp>][@<refresh>][i][m][eDd]

Additionals options can be provided following the mode, using a comma to separate each option. Valid options can be found in modedb default video mode support.

The intermediate drm_cmdline_mode structure is required to store additional options from the command line modline like the force-enable/disable flag.

Return

True if a valid modeline has been parsed, false otherwise.

struct drm_display_mode *drm_mode_create_from_cmdline_mode(struct drm_device *dev, struct drm_cmdline_mode *cmd)¶: convert a command line modeline into a DRM display mode

Parameters

struct drm_device *dev: DRM device to create the new mode for
struct drm_cmdline_mode *cmd: input command line modeline

Return

Pointer to converted mode on success, NULL on error.

bool drm_mode_is_420_only(const struct drm_display_info *display, const struct drm_display_mode *mode)¶: if a given videomode can be only supported in YCBCR420 output format

Parameters

const struct drm_display_info *display: display under action
const struct drm_display_mode *mode: video mode to be tested.

Return

true if the mode can be supported in YCBCR420 format false if not.

bool drm_mode_is_420_also(const struct drm_display_info *display, const struct drm_display_mode *mode)¶: if a given videomode can be supported in YCBCR420 output format also (along with RGB/YCBCR444/422)

Parameters

const struct drm_display_info *display: display under action.
const struct drm_display_mode *mode: video mode to be tested.

Return

true if the mode can be support YCBCR420 format false if not.

bool drm_mode_is_420(const struct drm_display_info *display, const struct drm_display_mode *mode)¶: if a given videomode can be supported in YCBCR420 output format

Parameters

const struct drm_display_info *display: display under action.
const struct drm_display_mode *mode: video mode to be tested.

Return

true if the mode can be supported in YCBCR420 format false if not.

Connector Abstraction¶

In DRM connectors are the general abstraction for display sinks, and include also fixed panels or anything else that can display pixels in some form. As opposed to all other KMS objects representing hardware (like CRTC, encoder or plane abstractions) connectors can be hotplugged and unplugged at runtime. Hence they are reference-counted using drm_connector_get() and drm_connector_put().

KMS driver must create, initialize, register and attach at a struct drm_connector for each such sink. The instance is created as other KMS objects and initialized by setting the following fields. The connector is initialized with a call to drm_connector_init() with a pointer to the struct drm_connector_funcs and a connector type, and then exposed to userspace with a call to drm_connector_register().

Connectors must be attached to an encoder to be used. For devices that map connectors to encoders 1:1, the connector should be attached at initialization time with a call to drm_connector_attach_encoder(). The driver must also set the drm_connector.encoder field to point to the attached encoder.

For connectors which are not fixed (like built-in panels) the driver needs to support hotplug notifications. The simplest way to do that is by using the probe helpers, see drm_kms_helper_poll_init() for connectors which don’t have hardware support for hotplug interrupts. Connectors with hardware hotplug support can instead use e.g. drm_helper_hpd_irq_event().

Connector Functions Reference¶

enum drm_connector_status¶: status for a drm_connector

Constants

connector_status_connected: The connector is definitely connected to a sink device, and can be enabled.
connector_status_disconnected: The connector isn’t connected to a sink device which can be autodetect. For digital outputs like DP or HDMI (which can be realiable probed) this means there’s really nothing there. It is driver-dependent whether a connector with this status can be lit up or not.
connector_status_unknown: The connector’s status could not be reliably detected. This happens when probing would either cause flicker (like load-detection when the connector is in use), or when a hardware resource isn’t available (like when load-detection needs a free CRTC). It should be possible to light up the connector with one of the listed fallback modes. For default configuration userspace should only try to light up connectors with unknown status when there’s not connector with connector_status_connected.

Description

This enum is used to track the connector status. There are no separate #defines for the uapi!

enum drm_connector_registration_state¶: userspace registration status for a drm_connector

Constants

DRM_CONNECTOR_INITIALIZING

The connector has just been created, but has yet to be exposed to userspace. There should be no additional restrictions to how the state of this connector may be modified.

DRM_CONNECTOR_REGISTERED

The connector has been fully initialized and registered with sysfs, as such it has been exposed to userspace. There should be no additional restrictions to how the state of this connector may be modified.

DRM_CONNECTOR_UNREGISTERED

The connector has either been exposed to userspace and has since been unregistered and removed from userspace, or the connector was unregistered before it had a chance to be exposed to userspace (e.g. still in the DRM_CONNECTOR_INITIALIZING state). When a connector is unregistered, there are additional restrictions to how its state may be modified:

An unregistered connector may only have its DPMS changed from On->Off. Once DPMS is changed to Off, it may not be switched back to On.
Modesets are not allowed on unregistered connectors, unless they would result in disabling its assigned CRTCs. This means disabling a CRTC on an unregistered connector is OK, but enabling one is not.
Removing a CRTC from an unregistered connector is OK, but new CRTCs may never be assigned to an unregistered connector.

Description

This enum is used to track the status of initializing a connector and registering it with userspace, so that DRM can prevent bogus modesets on connectors that no longer exist.

struct drm_scrambling¶: sink’s scrambling support.

Definition

struct drm_scrambling {
  bool supported;
  bool low_rates;
};

Members

supported: scrambling supported for rates > 340 Mhz.
low_rates: scrambling supported for rates <= 340 Mhz.

struct drm_hdmi_dsc_cap¶: DSC capabilities of HDMI sink

Definition

struct drm_hdmi_dsc_cap {
  bool v_1p2;
  bool native_420;
  bool all_bpp;
  u8 bpc_supported;
  u8 max_slices;
  int clk_per_slice;
  u8 max_lanes;
  u8 max_frl_rate_per_lane;
  u8 total_chunk_kbytes;
};

Members

v_1p2: flag for dsc1.2 version support by sink
native_420: Does sink support DSC with 4:2:0 compression
all_bpp: Does sink support all bpp with 4:4:4: or 4:2:2 compressed formats
bpc_supported: compressed bpc supported by sink : 10, 12 or 16 bpc
max_slices: maximum number of Horizontal slices supported by
clk_per_slice: max pixel clock in MHz supported per slice
max_lanes: dsc max lanes supported for Fixed rate Link training
max_frl_rate_per_lane: maximum frl rate with DSC per lane
total_chunk_kbytes: max size of chunks in KBs supported per line

Description

Describes the DSC support provided by HDMI 2.1 sink. The information is fetched fom additional HFVSDB blocks defined for HDMI 2.1.

struct drm_hdmi_info¶: runtime information about the connected HDMI sink

Definition

struct drm_hdmi_info {
  struct drm_scdc scdc;
  unsigned long y420_vdb_modes[BITS_TO_LONGS(256)];
  unsigned long y420_cmdb_modes[BITS_TO_LONGS(256)];
  u64 y420_cmdb_map;
  u8 y420_dc_modes;
  u8 max_frl_rate_per_lane;
  u8 max_lanes;
  struct drm_hdmi_dsc_cap dsc_cap;
};

Members

scdc: sink’s scdc support and capabilities
y420_vdb_modes: bitmap of modes which can support ycbcr420 output only (not normal RGB/YCBCR444/422 outputs). The max VIC defined by the CEA-861-G spec is 219, so the size is 256 bits to map up to 256 VICs.
y420_cmdb_modes: bitmap of modes which can support ycbcr420 output also, along with normal HDMI outputs. The max VIC defined by the CEA-861-G spec is 219, so the size is 256 bits to map up to 256 VICs.
y420_cmdb_map: bitmap of SVD index, to extraxt vcb modes
y420_dc_modes: bitmap of deep color support index
max_frl_rate_per_lane: support fixed rate link
max_lanes: supported by sink
dsc_cap: DSC capabilities of the sink

Description

Describes if a given display supports advanced HDMI 2.0 features. This information is available in CEA-861-F extension blocks (like HF-VSDB).

enum drm_link_status¶: connector’s link_status property value

Constants

DRM_LINK_STATUS_GOOD: DP Link is Good as a result of successful link training
DRM_LINK_STATUS_BAD: DP Link is BAD as a result of link training failure

Description

This enum is used as the connector’s link status property value. It is set to the values defined in uapi.

enum drm_panel_orientation¶: panel_orientation info for drm_display_info

Constants

DRM_MODE_PANEL_ORIENTATION_UNKNOWN: The drm driver has not provided any panel orientation information (normal for non panels) in this case the “panel orientation” connector prop will not be attached.
DRM_MODE_PANEL_ORIENTATION_NORMAL: The top side of the panel matches the top side of the device’s casing.
DRM_MODE_PANEL_ORIENTATION_BOTTOM_UP: The top side of the panel matches the bottom side of the device’s casing, iow the panel is mounted upside-down.
DRM_MODE_PANEL_ORIENTATION_LEFT_UP: The left side of the panel matches the top side of the device’s casing.
DRM_MODE_PANEL_ORIENTATION_RIGHT_UP: The right side of the panel matches the top side of the device’s casing.

Description

This enum is used to track the (LCD) panel orientation. There are no separate #defines for the uapi!

struct drm_monitor_range_info¶: Panel’s Monitor range in EDID for drm_display_info

Definition

struct drm_monitor_range_info {
  u16 min_vfreq;
  u16 max_vfreq;
};

Members

min_vfreq: This is the min supported refresh rate in Hz from EDID’s detailed monitor range.
max_vfreq: This is the max supported refresh rate in Hz from EDID’s detailed monitor range

Description

This struct is used to store a frequency range supported by panel as parsed from EDID’s detailed monitor range descriptor block.

struct drm_luminance_range_info¶: Panel’s luminance range for drm_display_info. Calculated using data in EDID

Definition

struct drm_luminance_range_info {
  u32 min_luminance;
  u32 max_luminance;
};

Members

min_luminance: This is the min supported luminance value
max_luminance: This is the max supported luminance value

Description

This struct is used to store a luminance range supported by panel as calculated using data from EDID’s static hdr metadata.

enum drm_privacy_screen_status¶: privacy screen status

Constants

PRIVACY_SCREEN_DISABLED

The privacy-screen on the panel is disabled

PRIVACY_SCREEN_ENABLED

The privacy-screen on the panel is enabled

PRIVACY_SCREEN_DISABLED_LOCKED

The privacy-screen on the panel is disabled and locked (cannot be changed)

PRIVACY_SCREEN_ENABLED_LOCKED

The privacy-screen on the panel is enabled and locked (cannot be changed)

Description

This enum is used to track and control the state of the integrated privacy screen present on some display panels, via the “privacy-screen sw-state” and “privacy-screen hw-state” properties. Note the _LOCKED enum values are only valid for the “privacy-screen hw-state” property.

enum drm_bus_flags¶: bus_flags info for drm_display_info

Constants

DRM_BUS_FLAG_DE_LOW: The Data Enable signal is active low
DRM_BUS_FLAG_DE_HIGH: The Data Enable signal is active high
DRM_BUS_FLAG_PIXDATA_DRIVE_POSEDGE: Data is driven on the rising edge of the pixel clock
DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE: Data is driven on the falling edge of the pixel clock
DRM_BUS_FLAG_PIXDATA_SAMPLE_POSEDGE: Data is sampled on the rising edge of the pixel clock
DRM_BUS_FLAG_PIXDATA_SAMPLE_NEGEDGE: Data is sampled on the falling edge of the pixel clock
DRM_BUS_FLAG_DATA_MSB_TO_LSB: Data is transmitted MSB to LSB on the bus
DRM_BUS_FLAG_DATA_LSB_TO_MSB: Data is transmitted LSB to MSB on the bus
DRM_BUS_FLAG_SYNC_DRIVE_POSEDGE: Sync signals are driven on the rising edge of the pixel clock
DRM_BUS_FLAG_SYNC_DRIVE_NEGEDGE: Sync signals are driven on the falling edge of the pixel clock
DRM_BUS_FLAG_SYNC_SAMPLE_POSEDGE: Sync signals are sampled on the rising edge of the pixel clock
DRM_BUS_FLAG_SYNC_SAMPLE_NEGEDGE: Sync signals are sampled on the falling edge of the pixel clock
DRM_BUS_FLAG_SHARP_SIGNALS: Set if the Sharp-specific signals (SPL, CLS, PS, REV) must be used

Description

This enum defines signal polarities and clock edge information for signals on a bus as bitmask flags.

The clock edge information is conveyed by two sets of symbols, DRM_BUS_FLAGS_*_DRIVE_* and DRM_BUS_FLAGS_*_SAMPLE_*. When this enum is used to describe a bus from the point of view of the transmitter, the *_DRIVE_* flags should be used. When used from the point of view of the receiver, the *_SAMPLE_* flags should be used. The *_DRIVE_* and *_SAMPLE_* flags alias each other, with the *_SAMPLE_POSEDGE and *_SAMPLE_NEGEDGE flags being equal to *_DRIVE_NEGEDGE and *_DRIVE_POSEDGE respectively. This simplifies code as signals are usually sampled on the opposite edge of the driving edge. Transmitters and receivers may however need to take other signal timings into account to convert between driving and sample edges.

struct drm_display_info¶: runtime data about the connected sink

Definition

struct drm_display_info {
  unsigned int width_mm;
  unsigned int height_mm;
  unsigned int bpc;
  enum subpixel_order subpixel_order;
#define DRM_COLOR_FORMAT_RGB444         (1<<0);
#define DRM_COLOR_FORMAT_YCBCR444       (1<<1);
#define DRM_COLOR_FORMAT_YCBCR422       (1<<2);
#define DRM_COLOR_FORMAT_YCBCR420       (1<<3);
  int panel_orientation;
  u32 color_formats;
  const u32 *bus_formats;
  unsigned int num_bus_formats;
  u32 bus_flags;
  int max_tmds_clock;
  bool dvi_dual;
  bool is_hdmi;
  bool has_hdmi_infoframe;
  bool rgb_quant_range_selectable;
  u8 edid_hdmi_rgb444_dc_modes;
  u8 edid_hdmi_ycbcr444_dc_modes;
  u8 cea_rev;
  struct drm_hdmi_info hdmi;
  bool non_desktop;
  struct drm_monitor_range_info monitor_range;
  struct drm_luminance_range_info luminance_range;
  u8 mso_stream_count;
  u8 mso_pixel_overlap;
  u32 max_dsc_bpp;
};

Members

width_mm

Physical width in mm.

height_mm

Physical height in mm.

bpc

Maximum bits per color channel. Used by HDMI and DP outputs.

subpixel_order

Subpixel order of LCD panels.

panel_orientation

Read only connector property for built-in panels, indicating the orientation of the panel vs the device’s casing. drm_connector_init() sets this to DRM_MODE_PANEL_ORIENTATION_UNKNOWN. When not UNKNOWN this gets used by the drm_fb_helpers to rotate the fb to compensate and gets exported as prop to userspace.

color_formats

HDMI Color formats, selects between RGB and YCrCb modes. Used DRM_COLOR_FORMAT_ defines, which are _not_ the same ones as used to describe the pixel format in framebuffers, and also don’t match the formats in bus_formats which are shared with v4l.

bus_formats

Pixel data format on the wire, somewhat redundant with color_formats. Array of size num_bus_formats encoded using MEDIA_BUS_FMT_ defines shared with v4l and media drivers.

num_bus_formats

Size of bus_formats array.

bus_flags

Additional information (like pixel signal polarity) for the pixel data on the bus, using enum drm_bus_flags values DRM_BUS_FLAGS_.

max_tmds_clock

Maximum TMDS clock rate supported by the sink in kHz. 0 means undefined.

dvi_dual

Dual-link DVI sink?

is_hdmi

True if the sink is an HDMI device.

This field shall be used instead of calling drm_detect_hdmi_monitor() when possible.

has_hdmi_infoframe

Does the sink support the HDMI infoframe?

rgb_quant_range_selectable

Does the sink support selecting the RGB quantization range?

edid_hdmi_rgb444_dc_modes

Mask of supported hdmi deep color modes in RGB 4:4:4. Even more stuff redundant with bus_formats.

edid_hdmi_ycbcr444_dc_modes

Mask of supported hdmi deep color modes in YCbCr 4:4:4. Even more stuff redundant with bus_formats.

cea_rev

CEA revision of the HDMI sink.

hdmi

advance features of a HDMI sink.

non_desktop

Non desktop display (HMD).

monitor_range

Frequency range supported by monitor range descriptor

luminance_range

Luminance range supported by panel

mso_stream_count

eDP Multi-SST Operation (MSO) stream count from the DisplayID VESA vendor block. 0 for conventional Single-Stream Transport (SST), or 2 or 4 MSO streams.

mso_pixel_overlap

eDP MSO segment pixel overlap, 0-8 pixels.

max_dsc_bpp

Maximum DSC target bitrate, if it is set to 0 the monitor’s default value is used instead.

Description

Describes a given display (e.g. CRT or flat panel) and its limitations. For fixed display sinks like built-in panels there’s not much difference between this and struct drm_connector. But for sinks with a real cable this structure is meant to describe all the things at the other end of the cable.

For sinks which provide an EDID this can be filled out by calling drm_add_edid_modes().

struct drm_connector_tv_margins¶: TV connector related margins

Definition

struct drm_connector_tv_margins {
  unsigned int bottom;
  unsigned int left;
  unsigned int right;
  unsigned int top;
};

Members

bottom: Bottom margin in pixels.
left: Left margin in pixels.
right: Right margin in pixels.
top: Top margin in pixels.

Description

Describes the margins in pixels to put around the image on TV connectors to deal with overscan.

struct drm_tv_connector_state¶: TV connector related states

Definition

struct drm_tv_connector_state {
  enum drm_mode_subconnector subconnector;
  struct drm_connector_tv_margins margins;
  unsigned int mode;
  unsigned int brightness;
  unsigned int contrast;
  unsigned int flicker_reduction;
  unsigned int overscan;
  unsigned int saturation;
  unsigned int hue;
};

Members

subconnector: selected subconnector
margins: TV margins
mode: TV mode
brightness: brightness in percent
contrast: contrast in percent
flicker_reduction: flicker reduction in percent
overscan: overscan in percent
saturation: saturation in percent
hue: hue in percent

struct drm_connector_state¶: mutable connector state

Definition

struct drm_connector_state {
  struct drm_connector *connector;
  struct drm_crtc *crtc;
  struct drm_encoder *best_encoder;
  enum drm_link_status link_status;
  struct drm_atomic_state *state;
  struct drm_crtc_commit *commit;
  struct drm_tv_connector_state tv;
  bool self_refresh_aware;
  enum hdmi_picture_aspect picture_aspect_ratio;
  unsigned int content_type;
  unsigned int hdcp_content_type;
  unsigned int scaling_mode;
  unsigned int content_protection;
  u32 colorspace;
  struct drm_writeback_job *writeback_job;
  u8 max_requested_bpc;
  u8 max_bpc;
  enum drm_privacy_screen_status privacy_screen_sw_state;
  struct drm_property_blob *hdr_output_metadata;
};

Members

connector

backpointer to the connector

crtc

CRTC to connect connector to, NULL if disabled.

Do not change this directly, use drm_atomic_set_crtc_for_connector() instead.

best_encoder

Used by the atomic helpers to select the encoder, through the drm_connector_helper_funcs.atomic_best_encoder or drm_connector_helper_funcs.best_encoder callbacks.

This is also used in the atomic helpers to map encoders to their current and previous connectors, see drm_atomic_get_old_connector_for_encoder() and drm_atomic_get_new_connector_for_encoder().

NOTE: Atomic drivers must fill this out (either themselves or through helpers), for otherwise the GETCONNECTOR and GETENCODER IOCTLs will not return correct data to userspace.

link_status

Connector link_status to keep track of whether link is GOOD or BAD to notify userspace if retraining is necessary.

state

backpointer to global drm_atomic_state

commit

Tracks the pending commit to prevent use-after-free conditions.

Is only set when crtc is NULL.

tv

TV connector state

self_refresh_aware

This tracks whether a connector is aware of the self refresh state. It should be set to true for those connector implementations which understand the self refresh state. This is needed since the crtc registers the self refresh helpers and it doesn’t know if the connectors downstream have implemented self refresh entry/exit.

Drivers should set this to true in atomic_check if they know how to handle self_refresh requests.

picture_aspect_ratio

Connector property to control the HDMI infoframe aspect ratio setting.

The DRM_MODE_PICTURE_ASPECT_* values much match the values for enum hdmi_picture_aspect

content_type

Connector property to control the HDMI infoframe content type setting. The DRM_MODE_CONTENT_TYPE_* values much match the values.

hdcp_content_type

Connector property to pass the type of protected content. This is most commonly used for HDCP.

scaling_mode

Connector property to control the upscaling, mostly used for built-in panels.

content_protection

Connector property to request content protection. This is most commonly used for HDCP.

colorspace

State variable for Connector property to request colorspace change on Sink. This is most commonly used to switch to wider color gamuts like BT2020.

writeback_job

Writeback job for writeback connectors

Holds the framebuffer and out-fence for a writeback connector. As the writeback completion may be asynchronous to the normal commit cycle, the writeback job lifetime is managed separately from the normal atomic state by this object.

max_requested_bpc

Connector property to limit the maximum bit depth of the pixels.

max_bpc

Connector max_bpc based on the requested max_bpc property and the connector bpc limitations obtained from edid.

privacy_screen_sw_state

See Standard Connector Properties

hdr_output_metadata

DRM blob property for HDR output metadata

struct drm_connector_funcs¶: control connectors on a given device

Definition

struct drm_connector_funcs {
  int (*dpms)(struct drm_connector *connector, int mode);
  void (*reset)(struct drm_connector *connector);
  enum drm_connector_status (*detect)(struct drm_connector *connector, bool force);
  void (*force)(struct drm_connector *connector);
  int (*fill_modes)(struct drm_connector *connector, uint32_t max_width, uint32_t max_height);
  int (*set_property)(struct drm_connector *connector, struct drm_property *property, uint64_t val);
  int (*late_register)(struct drm_connector *connector);
  void (*early_unregister)(struct drm_connector *connector);
  void (*destroy)(struct drm_connector *connector);
  struct drm_connector_state *(*atomic_duplicate_state)(struct drm_connector *connector);
  void (*atomic_destroy_state)(struct drm_connector *connector, struct drm_connector_state *state);
  int (*atomic_set_property)(struct drm_connector *connector,struct drm_connector_state *state,struct drm_property *property, uint64_t val);
  int (*atomic_get_property)(struct drm_connector *connector,const struct drm_connector_state *state,struct drm_property *property, uint64_t *val);
  void (*atomic_print_state)(struct drm_printer *p, const struct drm_connector_state *state);
  void (*oob_hotplug_event)(struct drm_connector *connector);
  void (*debugfs_init)(struct drm_connector *connector, struct dentry *root);
};

Members

dpms

Legacy entry point to set the per-connector DPMS state. Legacy DPMS is exposed as a standard property on the connector, but diverted to this callback in the drm core. Note that atomic drivers don’t implement the 4 level DPMS support on the connector any more, but instead only have an on/off “ACTIVE” property on the CRTC object.

This hook is not used by atomic drivers, remapping of the legacy DPMS property is entirely handled in the DRM core.

RETURNS:

0 on success or a negative error code on failure.

reset

Reset connector hardware and software state to off. This function isn’t called by the core directly, only through drm_mode_config_reset(). It’s not a helper hook only for historical reasons.

Atomic drivers can use drm_atomic_helper_connector_reset() to reset atomic state using this hook.

detect

Check to see if anything is attached to the connector. The parameter force is set to false whilst polling, true when checking the connector due to a user request. force can be used by the driver to avoid expensive, destructive operations during automated probing.

This callback is optional, if not implemented the connector will be considered as always being attached.

FIXME:

Note that this hook is only called by the probe helper. It’s not in the helper library vtable purely for historical reasons. The only DRM core entry point to probe connector state is fill_modes.

Note that the helper library will already hold drm_mode_config.connection_mutex. Drivers which need to grab additional locks to avoid races with concurrent modeset changes need to use drm_connector_helper_funcs.detect_ctx instead.

Also note that this callback can be called no matter the state the connector is in. Drivers that need the underlying device to be powered to perform the detection will first need to make sure it’s been properly enabled.

RETURNS:

drm_connector_status indicating the connector’s status.

force

This function is called to update internal encoder state when the connector is forced to a certain state by userspace, either through the sysfs interfaces or on the kernel cmdline. In that case the detect callback isn’t called.

FIXME:

Note that this hook is only called by the probe helper. It’s not in the helper library vtable purely for historical reasons. The only DRM core entry point to probe connector state is fill_modes.

fill_modes

Entry point for output detection and basic mode validation. The driver should reprobe the output if needed (e.g. when hotplug handling is unreliable), add all detected modes to drm_connector.modes and filter out any the device can’t support in any configuration. It also needs to filter out any modes wider or higher than the parameters max_width and max_height indicate.

The drivers must also prune any modes no longer valid from drm_connector.modes. Furthermore it must update drm_connector.status and drm_connector.edid. If no EDID has been received for this output connector->edid must be NULL.

Drivers using the probe helpers should use drm_helper_probe_single_connector_modes() to implement this function.

RETURNS:

The number of modes detected and filled into drm_connector.modes.

set_property

This is the legacy entry point to update a property attached to the connector.

This callback is optional if the driver does not support any legacy driver-private properties. For atomic drivers it is not used because property handling is done entirely in the DRM core.

RETURNS:

0 on success or a negative error code on failure.

late_register

This optional hook can be used to register additional userspace interfaces attached to the connector, light backlight control, i2c, DP aux or similar interfaces. It is called late in the driver load sequence from drm_connector_register() when registering all the core drm connector interfaces. Everything added from this callback should be unregistered in the early_unregister callback.

This is called while holding drm_connector.mutex.

Returns:

0 on success, or a negative error code on failure.

early_unregister

This optional hook should be used to unregister the additional userspace interfaces attached to the connector from late_register(). It is called from drm_connector_unregister(), early in the driver unload sequence to disable userspace access before data structures are torndown.

This is called while holding drm_connector.mutex.

destroy

Clean up connector resources. This is called at driver unload time through drm_mode_config_cleanup(). It can also be called at runtime when a connector is being hot-unplugged for drivers that support connector hotplugging (e.g. DisplayPort MST).

atomic_duplicate_state

Duplicate the current atomic state for this connector and return it. The core and helpers guarantee that any atomic state duplicated with this hook and still owned by the caller (i.e. not transferred to the driver by calling drm_mode_config_funcs.atomic_commit) will be cleaned up by calling the atomic_destroy_state hook in this structure.

This callback is mandatory for atomic drivers.

Atomic drivers which don’t subclass struct drm_connector_state should use drm_atomic_helper_connector_duplicate_state(). Drivers that subclass the state structure to extend it with driver-private state should use __drm_atomic_helper_connector_duplicate_state() to make sure shared state is duplicated in a consistent fashion across drivers.

It is an error to call this hook before drm_connector.state has been initialized correctly.

NOTE:

If the duplicate state references refcounted resources this hook must acquire a reference for each of them. The driver must release these references again in atomic_destroy_state.

RETURNS:

Duplicated atomic state or NULL when the allocation failed.

atomic_destroy_state

Destroy a state duplicated with atomic_duplicate_state and release or unreference all resources it references

This callback is mandatory for atomic drivers.

atomic_set_property

Decode a driver-private property value and store the decoded value into the passed-in state structure. Since the atomic core decodes all standardized properties (even for extensions beyond the core set of properties which might not be implemented by all drivers) this requires drivers to subclass the state structure.

Such driver-private properties should really only be implemented for truly hardware/vendor specific state. Instead it is preferred to standardize atomic extension and decode the properties used to expose such an extension in the core.

Do not call this function directly, use drm_atomic_connector_set_property() instead.

This callback is optional if the driver does not support any driver-private atomic properties.

NOTE:

This function is called in the state assembly phase of atomic modesets, which can be aborted for any reason (including on userspace’s request to just check whether a configuration would be possible). Drivers MUST NOT touch any persistent state (hardware or software) or data structures except the passed in state parameter.

Also since userspace controls in which order properties are set this function must not do any input validation (since the state update is incomplete and hence likely inconsistent). Instead any such input validation must be done in the various atomic_check callbacks.

RETURNS:

0 if the property has been found, -EINVAL if the property isn’t implemented by the driver (which shouldn’t ever happen, the core only asks for properties attached to this connector). No other validation is allowed by the driver. The core already checks that the property value is within the range (integer, valid enum value, …) the driver set when registering the property.

atomic_get_property

Reads out the decoded driver-private property. This is used to implement the GETCONNECTOR IOCTL.

Do not call this function directly, use drm_atomic_connector_get_property() instead.

This callback is optional if the driver does not support any driver-private atomic properties.

RETURNS:

0 on success, -EINVAL if the property isn’t implemented by the driver (which shouldn’t ever happen, the core only asks for properties attached to this connector).

atomic_print_state

If driver subclasses struct drm_connector_state, it should implement this optional hook for printing additional driver specific state.

Do not call this directly, use drm_atomic_connector_print_state() instead.

oob_hotplug_event

This will get called when a hotplug-event for a drm-connector has been received from a source outside the display driver / device.

debugfs_init

Allows connectors to create connector-specific debugfs files.

Description

Each CRTC may have one or more connectors attached to it. The functions below allow the core DRM code to control connectors, enumerate available modes, etc.

struct drm_cmdline_mode¶: DRM Mode passed through the kernel command-line

Definition

struct drm_cmdline_mode {
  char name[DRM_DISPLAY_MODE_LEN];
  bool specified;
  bool refresh_specified;
  bool bpp_specified;
  int xres;
  int yres;
  int bpp;
  int refresh;
  bool rb;
  bool interlace;
  bool cvt;
  bool margins;
  enum drm_connector_force force;
  unsigned int rotation_reflection;
  enum drm_panel_orientation panel_orientation;
  struct drm_connector_tv_margins tv_margins;
};

Members

name: Name of the mode.
specified: Has a mode been read from the command-line?
refresh_specified: Did the mode have a preferred refresh rate?
bpp_specified: Did the mode have a preferred BPP?
xres: Active resolution on the X axis, in pixels.
yres: Active resolution on the Y axis, in pixels.
bpp: Bits per pixels for the mode.
refresh: Refresh rate, in Hertz.
rb: Do we need to use reduced blanking?
interlace: The mode is interlaced.
cvt: The timings will be calculated using the VESA Coordinated Video Timings instead of looking up the mode from a table.
margins: Add margins to the mode calculation (1.8% of xres rounded down to 8 pixels and 1.8% of yres).
force: Ignore the hotplug state of the connector, and force its state to one of the DRM_FORCE_* values.
rotation_reflection: Initial rotation and reflection of the mode setup from the command line. See DRM_MODE_ROTATE_* and DRM_MODE_REFLECT_*. The only rotations supported are DRM_MODE_ROTATE_0 and DRM_MODE_ROTATE_180.
panel_orientation: drm-connector “panel orientation” property override value, DRM_MODE_PANEL_ORIENTATION_UNKNOWN if not set.
tv_margins: TV margins to apply to the mode.

Description

Each connector can have an initial mode with additional options passed through the kernel command line. This structure allows to express those parameters and will be filled by the command-line parser.

struct drm_connector¶: central DRM connector control structure

Definition

struct drm_connector {
  struct drm_device *dev;
  struct device *kdev;
  struct device_attribute *attr;
  struct fwnode_handle *fwnode;
  struct list_head head;
  struct list_head global_connector_list_entry;
  struct drm_mode_object base;
  char *name;
  struct mutex mutex;
  unsigned index;
  int connector_type;
  int connector_type_id;
  bool interlace_allowed;
  bool doublescan_allowed;
  bool stereo_allowed;
  bool ycbcr_420_allowed;
  enum drm_connector_registration_state registration_state;
  struct list_head modes;
  enum drm_connector_status status;
  struct list_head probed_modes;
  struct drm_display_info display_info;
  const struct drm_connector_funcs *funcs;
  struct drm_property_blob *edid_blob_ptr;
  struct drm_object_properties properties;
  struct drm_property *scaling_mode_property;
  struct drm_property *vrr_capable_property;
  struct drm_property *colorspace_property;
  struct drm_property_blob *path_blob_ptr;
  struct drm_property *max_bpc_property;
  struct drm_privacy_screen *privacy_screen;
  struct notifier_block privacy_screen_notifier;
  struct drm_property *privacy_screen_sw_state_property;
  struct drm_property *privacy_screen_hw_state_property;
#define DRM_CONNECTOR_POLL_HPD (1 << 0);
#define DRM_CONNECTOR_POLL_CONNECT (1 << 1);
#define DRM_CONNECTOR_POLL_DISCONNECT (1 << 2);
  uint8_t polled;
  int dpms;
  const struct drm_connector_helper_funcs *helper_private;
  struct drm_cmdline_mode cmdline_mode;
  enum drm_connector_force force;
  bool override_edid;
  u64 epoch_counter;
  u32 possible_encoders;
  struct drm_encoder *encoder;
#define MAX_ELD_BYTES   128;
  uint8_t eld[MAX_ELD_BYTES];
  bool latency_present[2];
  int video_latency[2];
  int audio_latency[2];
  struct i2c_adapter *ddc;
  int null_edid_counter;
  unsigned bad_edid_counter;
  bool edid_corrupt;
  u8 real_edid_checksum;
  struct dentry *debugfs_entry;
  struct drm_connector_state *state;
  struct drm_property_blob *tile_blob_ptr;
  bool has_tile;
  struct drm_tile_group *tile_group;
  bool tile_is_single_monitor;
  uint8_t num_h_tile, num_v_tile;
  uint8_t tile_h_loc, tile_v_loc;
  uint16_t tile_h_size, tile_v_size;
  struct llist_node free_node;
  struct hdr_sink_metadata hdr_sink_metadata;
};

Members

dev

parent DRM device

kdev

kernel device for sysfs attributes

attr

sysfs attributes

fwnode

associated fwnode supplied by platform firmware

Drivers can set this to associate a fwnode with a connector, drivers are expected to get a reference on the fwnode when setting this. drm_connector_cleanup() will call fwnode_handle_put() on this.

head

List of all connectors on a dev, linked from drm_mode_config.connector_list. Protected by drm_mode_config.connector_list_lock, but please only use drm_connector_list_iter to walk this list.

global_connector_list_entry

Connector entry in the global connector-list, used by drm_connector_find_by_fwnode().

base

base KMS object

name

human readable name, can be overwritten by the driver

mutex

Lock for general connector state, but currently only protects registered. Most of the connector state is still protected by drm_mode_config.mutex.

index

Compacted connector index, which matches the position inside the mode_config.list for drivers not supporting hot-add/removing. Can be used as an array index. It is invariant over the lifetime of the connector.

connector_type

one of the DRM_MODE_CONNECTOR_<foo> types from drm_mode.h

connector_type_id

index into connector type enum

interlace_allowed

Can this connector handle interlaced modes? Only used by drm_helper_probe_single_connector_modes() for mode filtering.

doublescan_allowed

Can this connector handle doublescan? Only used by drm_helper_probe_single_connector_modes() for mode filtering.

stereo_allowed

Can this connector handle stereo modes? Only used by drm_helper_probe_single_connector_modes() for mode filtering.

ycbcr_420_allowed

This bool indicates if this connector is capable of handling YCBCR 420 output. While parsing the EDID blocks it’s very helpful to know if the source is capable of handling YCBCR 420 outputs.

registration_state

Is this connector initializing, exposed (registered) with userspace, or unregistered?

Protected by mutex.

modes

Modes available on this connector (from fill_modes() + user). Protected by drm_mode_config.mutex.

status

One of the drm_connector_status enums (connected, not, or unknown). Protected by drm_mode_config.mutex.

probed_modes

These are modes added by probing with DDC or the BIOS, before filtering is applied. Used by the probe helpers. Protected by drm_mode_config.mutex.

display_info

Display information is filled from EDID information when a display is detected. For non hot-pluggable displays such as flat panels in embedded systems, the driver should initialize the drm_display_info.width_mm and drm_display_info.height_mm fields with the physical size of the display.

Protected by drm_mode_config.mutex.

funcs

connector control functions

edid_blob_ptr

DRM property containing EDID if present. Protected by drm_mode_config.mutex. This should be updated only by calling drm_connector_update_edid_property().

properties

property tracking for this connector

scaling_mode_property

Optional atomic property to control the upscaling. See drm_connector_attach_content_protection_property().

vrr_capable_property

Optional property to help userspace query hardware support for variable refresh rate on a connector. connector. Drivers can add the property to a connector by calling drm_connector_attach_vrr_capable_property().

This should be updated only by calling drm_connector_set_vrr_capable_property().

colorspace_property

Connector property to set the suitable colorspace supported by the sink.

path_blob_ptr

DRM blob property data for the DP MST path property. This should only be updated by calling drm_connector_set_path_property().

max_bpc_property

Default connector property for the max bpc to be driven out of the connector.

privacy_screen

drm_privacy_screen for this connector, or NULL.

privacy_screen_notifier

privacy-screen notifier_block

privacy_screen_sw_state_property

Optional atomic property for the connector to control the integrated privacy screen.

privacy_screen_hw_state_property

Optional atomic property for the connector to report the actual integrated privacy screen state.

polled

Connector polling mode, a combination of

DRM_CONNECTOR_POLL_HPD: The connector generates hotplug events and doesn’t need to be periodically polled. The CONNECT and DISCONNECT flags must not be set together with the HPD flag.
DRM_CONNECTOR_POLL_CONNECT: Periodically poll the connector for connection.
DRM_CONNECTOR_POLL_DISCONNECT: Periodically poll the connector for disconnection, without causing flickering even when the connector is in use. DACs should rarely do this without a lot of testing.

Set to 0 for connectors that don’t support connection status discovery.

dpms

Current dpms state. For legacy drivers the drm_connector_funcs.dpms callback must update this. For atomic drivers, this is handled by the core atomic code, and drivers must only take drm_crtc_state.active into account.

helper_private

mid-layer private data

cmdline_mode

mode line parsed from the kernel cmdline for this connector

force

a DRM_FORCE_<foo> state for forced mode sets

override_edid

has the EDID been overwritten through debugfs for testing? Do not modify outside of drm_edid_override_set() and drm_edid_override_reset().

epoch_counter

used to detect any other changes in connector, besides status

possible_encoders

Bit mask of encoders that can drive this connector, drm_encoder_index() determines the index into the bitfield and the bits are set with drm_connector_attach_encoder().

encoder

Currently bound encoder driving this connector, if any. Only really meaningful for non-atomic drivers. Atomic drivers should instead look at drm_connector_state.best_encoder, and in case they need the CRTC driving this output, drm_connector_state.crtc.

eld

EDID-like data, if present

latency_present

AV delay info from ELD, if found

video_latency

Video latency info from ELD, if found. [0]: progressive, [1]: interlaced

audio_latency

audio latency info from ELD, if found [0]: progressive, [1]: interlaced

ddc

associated ddc adapter. A connector usually has its associated ddc adapter. If a driver uses this field, then an appropriate symbolic link is created in connector sysfs directory to make it easy for the user to tell which i2c adapter is for a particular display.

The field should be set by calling drm_connector_init_with_ddc().

null_edid_counter

track sinks that give us all zeros for the EDID. Needed to workaround some HW bugs where we get all 0s

bad_edid_counter

track sinks that give us an EDID with invalid checksum

edid_corrupt

Indicates whether the last read EDID was corrupt. Used in Displayport compliance testing - Displayport Link CTS Core 1.2 rev1.1 4.2.2.6

real_edid_checksum

real edid checksum for corrupted edid block. Required in Displayport 1.4 compliance testing rev1.1 4.2.2.6

debugfs_entry

debugfs directory for this connector

state

Current atomic state for this connector.

This is protected by drm_mode_config.connection_mutex. Note that nonblocking atomic commits access the current connector state without taking locks. Either by going through the struct drm_atomic_state pointers, see for_each_oldnew_connector_in_state(), for_each_old_connector_in_state() and for_each_new_connector_in_state(). Or through careful ordering of atomic commit operations as implemented in the atomic helpers, see struct drm_crtc_commit.

tile_blob_ptr

DRM blob property data for the tile property (used mostly by DP MST). This is meant for screens which are driven through separate display pipelines represented by drm_crtc, which might not be running with genlocked clocks. For tiled panels which are genlocked, like dual-link LVDS or dual-link DSI, the driver should try to not expose the tiling and virtualize both drm_crtc and drm_plane if needed.

This should only be updated by calling drm_connector_set_tile_property().

has_tile

is this connector connected to a tiled monitor

tile_group

tile group for the connected monitor

tile_is_single_monitor

whether the tile is one monitor housing

num_h_tile

number of horizontal tiles in the tile group

num_v_tile

number of vertical tiles in the tile group

tile_h_loc

horizontal location of this tile

tile_v_loc

vertical location of this tile

tile_h_size

horizontal size of this tile.

tile_v_size

vertical size of this tile.

free_node

List used only by drm_connector_list_iter to be able to clean up a connector from any context, in conjunction with drm_mode_config.connector_free_work.

hdr_sink_metadata

HDR Metadata Information read from sink

Description

Each connector may be connected to one or more CRTCs, or may be clonable by another connector if they can share a CRTC. Each connector also has a specific position in the broader display (referred to as a ‘screen’ though it could span multiple monitors).

struct drm_connector *drm_connector_lookup(struct drm_device *dev, struct drm_file *file_priv, uint32_t id)¶: lookup connector object

Parameters

struct drm_device *dev: DRM device
struct drm_file *file_priv: drm file to check for lease against.
uint32_t id: connector object id

Description

This function looks up the connector object specified by id add takes a reference to it.

void drm_connector_get(struct drm_connector *connector)¶: acquire a connector reference

Parameters

struct drm_connector *connector: DRM connector

Description

This function increments the connector’s refcount.

void drm_connector_put(struct drm_connector *connector)¶: release a connector reference

Parameters

struct drm_connector *connector: DRM connector

Description

This function decrements the connector’s reference count and frees the object if the reference count drops to zero.

bool drm_connector_is_unregistered(struct drm_connector *connector)¶: has the connector been unregistered from userspace?

Parameters

struct drm_connector *connector: DRM connector

Description

Checks whether or not connector has been unregistered from userspace.

Return

True if the connector was unregistered, false if the connector is registered or has not yet been registered with userspace.

struct drm_tile_group¶: Tile group metadata

Definition

struct drm_tile_group {
  struct kref refcount;
  struct drm_device *dev;
  int id;
  u8 group_data[8];
};

Members

refcount: reference count
dev: DRM device
id: tile group id exposed to userspace
group_data: Sink-private data identifying this group

Description

group_data corresponds to displayid vend/prod/serial for external screens with an EDID.

struct drm_connector_list_iter¶: connector_list iterator

Definition

struct drm_connector_list_iter {
};

Members

Description

This iterator tracks state needed to be able to walk the connector_list within struct drm_mode_config. Only use together with drm_connector_list_iter_begin(), drm_connector_list_iter_end() and drm_connector_list_iter_next() respectively the convenience macro drm_for_each_connector_iter().

Note that the return value of drm_connector_list_iter_next() is only valid up to the next drm_connector_list_iter_next() or drm_connector_list_iter_end() call. If you want to use the connector later, then you need to grab your own reference first using drm_connector_get().

drm_for_each_connector_iter¶

drm_for_each_connector_iter (connector, iter)

connector_list iterator macro

Parameters

connector: struct drm_connector pointer used as cursor
iter: struct drm_connector_list_iter

Description

Note that connector is only valid within the list body, if you want to use connector after calling drm_connector_list_iter_end() then you need to grab your own reference first using drm_connector_get().

drm_connector_for_each_possible_encoder¶

drm_connector_for_each_possible_encoder (connector, encoder)

iterate connector’s possible encoders

Parameters

connector: struct drm_connector pointer
encoder: struct drm_encoder pointer used as cursor

const char *drm_get_connector_type_name(unsigned int type)¶: return a string for connector type

Parameters

unsigned int type: The connector type (DRM_MODE_CONNECTOR_*)

Return

the name of the connector type, or NULL if the type is not valid.

int drm_connector_init(struct drm_device *dev, struct drm_connector *connector, const struct drm_connector_funcs *funcs, int connector_type)¶: Init a preallocated connector

Parameters

struct drm_device *dev: DRM device
struct drm_connector *connector: the connector to init
const struct drm_connector_funcs *funcs: callbacks for this connector
int connector_type: user visible type of the connector

Description

Initialises a preallocated connector. Connectors should be subclassed as part of driver connector objects.

At driver unload time the driver’s drm_connector_funcs.destroy hook should call drm_connector_cleanup() and free the connector structure. The connector structure should not be allocated with devm_kzalloc().

Note

consider using drmm_connector_init() instead of drm_connector_init() to let the DRM managed resource infrastructure take care of cleanup and deallocation.

Return

Zero on success, error code on failure.

int drm_connector_init_with_ddc(struct drm_device *dev, struct drm_connector *connector, const struct drm_connector_funcs *funcs, int connector_type, struct i2c_adapter *ddc)¶: Init a preallocated connector

Parameters

struct drm_device *dev: DRM device
struct drm_connector *connector: the connector to init
const struct drm_connector_funcs *funcs: callbacks for this connector
int connector_type: user visible type of the connector
struct i2c_adapter *ddc: pointer to the associated ddc adapter

Description

Initialises a preallocated connector. Connectors should be subclassed as part of driver connector objects.

At driver unload time the driver’s drm_connector_funcs.destroy hook should call drm_connector_cleanup() and free the connector structure. The connector structure should not be allocated with devm_kzalloc().

Ensures that the ddc field of the connector is correctly set.

Note

consider using drmm_connector_init() instead of drm_connector_init_with_ddc() to let the DRM managed resource infrastructure take care of cleanup and deallocation.

Return

Zero on success, error code on failure.

int drmm_connector_init(struct drm_device *dev, struct drm_connector *connector, const struct drm_connector_funcs *funcs, int connector_type, struct i2c_adapter *ddc)¶: Init a preallocated connector

Parameters

struct drm_device *dev: DRM device
struct drm_connector *connector: the connector to init
const struct drm_connector_funcs *funcs: callbacks for this connector
int connector_type: user visible type of the connector
struct i2c_adapter *ddc: optional pointer to the associated ddc adapter

Description

Initialises a preallocated connector. Connectors should be subclassed as part of driver connector objects.

Cleanup is automatically handled with a call to drm_connector_cleanup() in a DRM-managed action.

The connector structure should be allocated with drmm_kzalloc().

Return

Zero on success, error code on failure.

void drm_connector_attach_edid_property(struct drm_connector *connector)¶: attach edid property.

Parameters

struct drm_connector *connector: the connector

Description

Some connector types like DRM_MODE_CONNECTOR_VIRTUAL do not get a edid property attached by default. This function can be used to explicitly enable the edid property in these cases.

int drm_connector_attach_encoder(struct drm_connector *connector, struct drm_encoder *encoder)¶: attach a connector to an encoder

Parameters

struct drm_connector *connector: connector to attach
struct drm_encoder *encoder: encoder to attach connector to

Description

This function links up a connector to an encoder. Note that the routing restrictions between encoders and crtcs are exposed to userspace through the possible_clones and possible_crtcs bitmasks.

Return

Zero on success, negative errno on failure.

bool drm_connector_has_possible_encoder(struct drm_connector *connector, struct drm_encoder *encoder)¶: check if the connector and encoder are associated with each other

Parameters

struct drm_connector *connector: the connector
struct drm_encoder *encoder: the encoder

Return

True if encoder is one of the possible encoders for connector.

void drm_connector_cleanup(struct drm_connector *connector)¶: cleans up an initialised connector

Parameters

struct drm_connector *connector: connector to cleanup

Description

Cleans up the connector but doesn’t free the object.

int drm_connector_register(struct drm_connector *connector)¶: register a connector

Parameters

struct drm_connector *connector: the connector to register

Description

Register userspace interfaces for a connector. Only call this for connectors which can be hotplugged after drm_dev_register() has been called already, e.g. DP MST connectors. All other connectors will be registered automatically when calling drm_dev_register().

When the connector is no longer available, callers must call drm_connector_unregister().

Return

Zero on success, error code on failure.

void drm_connector_unregister(struct drm_connector *connector)¶: unregister a connector

Parameters

struct drm_connector *connector: the connector to unregister

Description

Unregister userspace interfaces for a connector. Only call this for connectors which have been registered explicitly by calling drm_connector_register().

const char *drm_get_connector_status_name(enum drm_connector_status status)¶: return a string for connector status

Parameters

enum drm_connector_status status: connector status to compute name of

Description

In contrast to the other drm_get_*_name functions this one here returns a const pointer and hence is threadsafe.

Return

connector status string

void drm_connector_list_iter_begin(struct drm_device *dev, struct drm_connector_list_iter *iter)¶: initialize a connector_list iterator

Parameters

struct drm_device *dev: DRM device
struct drm_connector_list_iter *iter: connector_list iterator

Description

Sets iter up to walk the drm_mode_config.connector_list of dev. iter must always be cleaned up again by calling drm_connector_list_iter_end(). Iteration itself happens using drm_connector_list_iter_next() or drm_for_each_connector_iter().

struct drm_connector *drm_connector_list_iter_next(struct drm_connector_list_iter *iter)¶: return next connector

Parameters

struct drm_connector_list_iter *iter: connector_list iterator

Return

the next connector for iter, or NULL when the list walk has completed.

void drm_connector_list_iter_end(struct drm_connector_list_iter *iter)¶: tear down a connector_list iterator

Parameters

struct drm_connector_list_iter *iter: connector_list iterator

Description

Tears down iter and releases any resources (like drm_connector references) acquired while walking the list. This must always be called, both when the iteration completes fully or when it was aborted without walking the entire list.

const char *drm_get_subpixel_order_name(enum subpixel_order order)¶: return a string for a given subpixel enum

Parameters

enum subpixel_order order: enum of subpixel_order

Description

Note you could abuse this and return something out of bounds, but that would be a caller error. No unscrubbed user data should make it here.

Return

string describing an enumerated subpixel property

int drm_display_info_set_bus_formats(struct drm_display_info *info, const u32 *formats, unsigned int num_formats)¶: set the supported bus formats

Parameters

struct drm_display_info *info: display info to store bus formats in
const u32 *formats: array containing the supported bus formats
unsigned int num_formats: the number of entries in the fmts array

Description

Store the supported bus formats in display info structure. See MEDIA_BUS_FMT_* definitions in include/uapi/linux/media-bus-format.h for a full list of available formats.

Return

0 on success or a negative error code on failure.

int drm_mode_create_dvi_i_properties(struct drm_device *dev)¶: create DVI-I specific connector properties

Parameters

struct drm_device *dev: DRM device

Description

Called by a driver the first time a DVI-I connector is made.

Return

0

void drm_connector_attach_dp_subconnector_property(struct drm_connector *connector)¶: create subconnector property for DP

Parameters

struct drm_connector *connector: drm_connector to attach property

Description

Called by a driver when DP connector is created.

int drm_connector_attach_content_type_property(struct drm_connector *connector)¶: attach content-type property

Parameters

struct drm_connector *connector: connector to attach content type property on.

Description

Called by a driver the first time a HDMI connector is made.

Return

0

void drm_connector_attach_tv_margin_properties(struct drm_connector *connector)¶: attach TV connector margin properties

Parameters

struct drm_connector *connector: DRM connector

Description

Called by a driver when it needs to attach TV margin props to a connector. Typically used on SDTV and HDMI connectors.

int drm_mode_create_tv_margin_properties(struct drm_device *dev)¶: create TV connector margin properties

Parameters

struct drm_device *dev: DRM device

Description

Called by a driver’s HDMI connector initialization routine, this function creates the TV margin properties for a given device. No need to call this function for an SDTV connector, it’s already called from drm_mode_create_tv_properties().

Return

0 on success or a negative error code on failure.

int drm_mode_create_tv_properties(struct drm_device *dev, unsigned int num_modes, const char *const modes[])¶: create TV specific connector properties

Parameters

struct drm_device *dev: DRM device
unsigned int num_modes: number of different TV formats (modes) supported
const char * const modes[]: array of pointers to strings containing name of each format

Description

Called by a driver’s TV initialization routine, this function creates the TV specific connector properties for a given device. Caller is responsible for allocating a list of format names and passing them to this routine.

Return

0 on success or a negative error code on failure.

int drm_mode_create_scaling_mode_property(struct drm_device *dev)¶: create scaling mode property

Parameters

struct drm_device *dev: DRM device

Description

Called by a driver the first time it’s needed, must be attached to desired connectors.

Atomic drivers should use drm_connector_attach_scaling_mode_property() instead to correctly assign drm_connector_state.scaling_mode in the atomic state.

Return

0

int drm_connector_attach_vrr_capable_property(struct drm_connector *connector)¶: creates the vrr_capable property

Parameters

struct drm_connector *connector: connector to create the vrr_capable property on.

Description

This is used by atomic drivers to add support for querying variable refresh rate capability for a connector.

Return

Zero on success, negative errno on failure.

int drm_connector_attach_scaling_mode_property(struct drm_connector *connector, u32 scaling_mode_mask)¶: attach atomic scaling mode property

Parameters

struct drm_connector *connector: connector to attach scaling mode property on.
u32 scaling_mode_mask: or’ed mask of BIT(DRM_MODE_SCALE_*).

Description

This is used to add support for scaling mode to atomic drivers. The scaling mode will be set to drm_connector_state.scaling_mode and can be used from drm_connector_helper_funcs->atomic_check for validation.

This is the atomic version of drm_mode_create_scaling_mode_property().

Return

Zero on success, negative errno on failure.

int drm_mode_create_aspect_ratio_property(struct drm_device *dev)¶: create aspect ratio property

Parameters

struct drm_device *dev: DRM device

Description

Called by a driver the first time it’s needed, must be attached to desired connectors.

Return

Zero on success, negative errno on failure.

int drm_mode_create_hdmi_colorspace_property(struct drm_connector *connector)¶: create hdmi colorspace property

Parameters

struct drm_connector *connector: connector to create the Colorspace property on.

Description

Called by a driver the first time it’s needed, must be attached to desired HDMI connectors.

Return

Zero on success, negative errno on failure.

int drm_mode_create_dp_colorspace_property(struct drm_connector *connector)¶: create dp colorspace property

Parameters

struct drm_connector *connector: connector to create the Colorspace property on.

Description

Called by a driver the first time it’s needed, must be attached to desired DP connectors.

Return

Zero on success, negative errno on failure.

int drm_mode_create_content_type_property(struct drm_device *dev)¶: create content type property

Parameters

struct drm_device *dev: DRM device

Description

Called by a driver the first time it’s needed, must be attached to desired connectors.

Return

Zero on success, negative errno on failure.

int drm_mode_create_suggested_offset_properties(struct drm_device *dev)¶: create suggests offset properties

Parameters

struct drm_device *dev: DRM device

Description

Create the suggested x/y offset property for connectors.

Return

0 on success or a negative error code on failure.

int drm_connector_set_path_property(struct drm_connector *connector, const char *path)¶: set tile property on connector

Parameters

struct drm_connector *connector: connector to set property on.
const char *path: path to use for property; must not be NULL.

Description

This creates a property to expose to userspace to specify a connector path. This is mainly used for DisplayPort MST where connectors have a topology and we want to allow userspace to give them more meaningful names.

Return

Zero on success, negative errno on failure.

int drm_connector_set_tile_property(struct drm_connector *connector)¶: set tile property on connector

Parameters

struct drm_connector *connector: connector to set property on.

Description

This looks up the tile information for a connector, and creates a property for userspace to parse if it exists. The property is of the form of 8 integers using ‘:’ as a separator. This is used for dual port tiled displays with DisplayPort SST or DisplayPort MST connectors.

Return

Zero on success, errno on failure.

void drm_connector_set_link_status_property(struct drm_connector *connector, uint64_t link_status)¶: Set link status property of a connector

Parameters

struct drm_connector *connector: drm connector
uint64_t link_status: new value of link status property (0: Good, 1: Bad)

Description

In usual working scenario, this link status property will always be set to “GOOD”. If something fails during or after a mode set, the kernel driver may set this link status property to “BAD”. The caller then needs to send a hotplug uevent for userspace to re-check the valid modes through GET_CONNECTOR_IOCTL and retry modeset.

The reason for adding this property is to handle link training failures, but it is not limited to DP or link training. For example, if we implement asynchronous setcrtc, this property can be used to report any failures in that.

Note

Drivers cannot rely on userspace to support this property and issue a modeset. As such, they may choose to handle issues (like re-training a link) without userspace’s intervention.

int drm_connector_attach_max_bpc_property(struct drm_connector *connector, int min, int max)¶: attach “max bpc” property

Parameters

struct drm_connector *connector: connector to attach max bpc property on.
int min: The minimum bit depth supported by the connector.
int max: The maximum bit depth supported by the connector.

Description

This is used to add support for limiting the bit depth on a connector.

Return

Zero on success, negative errno on failure.

int drm_connector_attach_hdr_output_metadata_property(struct drm_connector *connector)¶: attach “HDR_OUTPUT_METADA” property

Parameters

struct drm_connector *connector: connector to attach the property on.

Description

This is used to allow the userspace to send HDR Metadata to the driver.

Return

Zero on success, negative errno on failure.

int drm_connector_attach_colorspace_property(struct drm_connector *connector)¶: attach “Colorspace” property

Parameters

struct drm_connector *connector: connector to attach the property on.

Description

This is used to allow the userspace to signal the output colorspace to the driver.

Return

Zero on success, negative errno on failure.

bool drm_connector_atomic_hdr_metadata_equal(struct drm_connector_state *old_state, struct drm_connector_state *new_state)¶: checks if the hdr metadata changed

Parameters

struct drm_connector_state *old_state: old connector state to compare
struct drm_connector_state *new_state: new connector state to compare

Description

This is used by HDR-enabled drivers to test whether the HDR metadata have changed between two different connector state (and thus probably requires a full blown mode change).

Return

True if the metadata are equal, False otherwise

void drm_connector_set_vrr_capable_property(struct drm_connector *connector, bool capable)¶: sets the variable refresh rate capable property for a connector

Parameters

struct drm_connector *connector: drm connector
bool capable: True if the connector is variable refresh rate capable

Description

Should be used by atomic drivers to update the indicated support for variable refresh rate over a connector.

int drm_connector_set_panel_orientation(struct drm_connector *connector, enum drm_panel_orientation panel_orientation)¶: sets the connector’s panel_orientation

Parameters

struct drm_connector *connector: connector for which to set the panel-orientation property.
enum drm_panel_orientation panel_orientation: drm_panel_orientation value to set

Description

This function sets the connector’s panel_orientation and attaches a “panel orientation” property to the connector.

Calling this function on a connector where the panel_orientation has already been set is a no-op (e.g. the orientation has been overridden with a kernel commandline option).

It is allowed to call this function with a panel_orientation of DRM_MODE_PANEL_ORIENTATION_UNKNOWN, in which case it is a no-op.

The function shouldn’t be called in panel after drm is registered (i.e. drm_dev_register() is called in drm).

Return

Zero on success, negative errno on failure.

int drm_connector_set_panel_orientation_with_quirk(struct drm_connector *connector, enum drm_panel_orientation panel_orientation, int width, int height)¶: set the connector’s panel_orientation after checking for quirks

Parameters

struct drm_connector *connector: connector for which to init the panel-orientation property.
enum drm_panel_orientation panel_orientation: drm_panel_orientation value to set
int width: width in pixels of the panel, used for panel quirk detection
int height: height in pixels of the panel, used for panel quirk detection

Description

Like drm_connector_set_panel_orientation(), but with a check for platform specific (e.g. DMI based) quirks overriding the passed in panel_orientation.

Return

Zero on success, negative errno on failure.

int drm_connector_set_orientation_from_panel(struct drm_connector *connector, struct drm_panel *panel)¶: set the connector’s panel_orientation from panel’s callback.

Parameters

struct drm_connector *connector: connector for which to init the panel-orientation property.
struct drm_panel *panel: panel that can provide orientation information.

Description

Drm drivers should call this function before drm_dev_register(). Orientation is obtained from panel’s .get_orientation() callback.

Return

Zero on success, negative errno on failure.

void drm_connector_create_privacy_screen_properties(struct drm_connector *connector)¶: create the drm connecter’s privacy-screen properties.

Parameters

struct drm_connector *connector: connector for which to create the privacy-screen properties

Description

This function creates the “privacy-screen sw-state” and “privacy-screen hw-state” properties for the connector. They are not attached.

void drm_connector_attach_privacy_screen_properties(struct drm_connector *connector)¶: attach the drm connecter’s privacy-screen properties.

Parameters

struct drm_connector *connector: connector on which to attach the privacy-screen properties

Description

This function attaches the “privacy-screen sw-state” and “privacy-screen hw-state” properties to the connector. The initial state of both is set to “Disabled”.

void drm_connector_attach_privacy_screen_provider(struct drm_connector *connector, struct drm_privacy_screen *priv)¶: attach a privacy-screen to the connector

Parameters

struct drm_connector *connector: connector to attach the privacy-screen to
struct drm_privacy_screen *priv: drm_privacy_screen to attach

Description

Create and attach the standard privacy-screen properties and register a generic notifier for generating sysfs-connector-status-events on external changes to the privacy-screen status. This function takes ownership of the passed in drm_privacy_screen and will call drm_privacy_screen_put() on it when the connector is destroyed.

void drm_connector_update_privacy_screen(const struct drm_connector_state *connector_state)¶: update connector’s privacy-screen sw-state

Parameters

const struct drm_connector_state *connector_state: connector-state to update the privacy-screen for

Description

This function calls drm_privacy_screen_set_sw_state() on the connector’s privacy-screen.

If the connector has no privacy-screen, then this is a no-op.

void drm_connector_oob_hotplug_event(struct fwnode_handle *connector_fwnode)¶: Report out-of-band hotplug event to connector

Parameters

struct fwnode_handle *connector_fwnode: fwnode_handle to report the event on

Description

On some hardware a hotplug event notification may come from outside the display driver / device. An example of this is some USB Type-C setups where the hardware muxes the DisplayPort data and aux-lines but does not pass the altmode HPD status bit to the GPU’s DP HPD pin.

This function can be used to report these out-of-band events after obtaining a drm_connector reference through calling drm_connector_find_by_fwnode().

void drm_mode_put_tile_group(struct drm_device *dev, struct drm_tile_group *tg)¶: drop a reference to a tile group.

Parameters

struct drm_device *dev: DRM device
struct drm_tile_group *tg: tile group to drop reference to.

Description

drop reference to tile group and free if 0.

struct drm_tile_group *drm_mode_get_tile_group(struct drm_device *dev, const char topology[8])¶: get a reference to an existing tile group

Parameters

struct drm_device *dev: DRM device
const char topology[8]: 8-bytes unique per monitor.

Description

Use the unique bytes to get a reference to an existing tile group.

Return

tile group or NULL if not found.

struct drm_tile_group *drm_mode_create_tile_group(struct drm_device *dev, const char topology[8])¶: create a tile group from a displayid description

Parameters

struct drm_device *dev: DRM device
const char topology[8]: 8-bytes unique per monitor.

Description

Create a tile group for the unique monitor, and get a unique identifier for the tile group.

Return

new tile group or NULL.

Writeback Connectors¶

Writeback connectors are used to expose hardware which can write the output from a CRTC to a memory buffer. They are used and act similarly to other types of connectors, with some important differences:

Writeback connectors don’t provide a way to output visually to the user.
Writeback connectors are visible to userspace only when the client sets DRM_CLIENT_CAP_WRITEBACK_CONNECTORS.
Writeback connectors don’t have EDID.

A framebuffer may only be attached to a writeback connector when the connector is attached to a CRTC. The WRITEBACK_FB_ID property which sets the framebuffer applies only to a single commit (see below). A framebuffer may not be attached while the CRTC is off.

Unlike with planes, when a writeback framebuffer is removed by userspace DRM makes no attempt to remove it from active use by the connector. This is because no method is provided to abort a writeback operation, and in any case making a new commit whilst a writeback is ongoing is undefined (see WRITEBACK_OUT_FENCE_PTR below). As soon as the current writeback is finished, the framebuffer will automatically no longer be in active use. As it will also have already been removed from the framebuffer list, there will be no way for any userspace application to retrieve a reference to it in the intervening period.

Writeback connectors have some additional properties, which userspace can use to query and control them:

“WRITEBACK_FB_ID”:
Write-only object property storing a DRM_MODE_OBJECT_FB: it stores the framebuffer to be written by the writeback connector. This property is similar to the FB_ID property on planes, but will always read as zero and is not preserved across commits. Userspace must set this property to an output buffer every time it wishes the buffer to get filled.

“WRITEBACK_PIXEL_FORMATS”:
Immutable blob property to store the supported pixel formats table. The data is an array of u32 DRM_FORMAT_* fourcc values. Userspace can use this blob to find out what pixel formats are supported by the connector’s writeback engine.

“WRITEBACK_OUT_FENCE_PTR”:
Userspace can use this property to provide a pointer for the kernel to fill with a sync_file file descriptor, which will signal once the writeback is finished. The value should be the address of a 32-bit signed integer, cast to a u64. Userspace should wait for this fence to signal before making another commit affecting any of the same CRTCs, Planes or Connectors. Failure to do so will result in undefined behaviour. For this reason it is strongly recommended that all userspace applications making use of writeback connectors always retrieve an out-fence for the commit and use it appropriately. From userspace, this property will always read as zero.

struct drm_writeback_connector¶: DRM writeback connector

Definition

struct drm_writeback_connector {
  struct drm_connector base;
  struct drm_encoder encoder;
  struct drm_property_blob *pixel_formats_blob_ptr;
  spinlock_t job_lock;
  struct list_head job_queue;
  unsigned int fence_context;
  spinlock_t fence_lock;
  unsigned long fence_seqno;
  char timeline_name[32];
};

Members

base

base drm_connector object

encoder

Internal encoder used by the connector to fulfill the DRM framework requirements. The users of the drm_writeback_connector control the behaviour of the encoder by passing the enc_funcs parameter to drm_writeback_connector_init() function. For users of drm_writeback_connector_init_with_encoder(), this field is not valid as the encoder is managed within their drivers.

pixel_formats_blob_ptr

DRM blob property data for the pixel formats list on writeback connectors See also drm_writeback_connector_init()

job_lock

Protects job_queue

job_queue

Holds a list of a connector’s writeback jobs; the last item is the most recent. The first item may be either waiting for the hardware to begin writing, or currently being written.

fence_context

timeline context used for fence operations.

fence_lock

spinlock to protect the fences in the fence_context.

fence_seqno

Seqno variable used as monotonic counter for the fences created on the connector’s timeline.

timeline_name

The name of the connector’s fence timeline.

struct drm_writeback_job¶: DRM writeback job

Definition

struct drm_writeback_job {
  struct drm_writeback_connector *connector;
  bool prepared;
  struct work_struct cleanup_work;
  struct list_head list_entry;
  struct drm_framebuffer *fb;
  struct dma_fence *out_fence;
  void *priv;
};

Members

connector: Back-pointer to the writeback connector associated with the job
prepared: Set when the job has been prepared with drm_writeback_prepare_job()
cleanup_work: Used to allow drm_writeback_signal_completion to defer dropping the framebuffer reference to a workqueue
list_entry: List item for the writeback connector’s job_queue
fb: Framebuffer to be written to by the writeback connector. Do not set directly, use drm_writeback_set_fb()
out_fence: Fence which will signal once the writeback has completed
priv: Driver-private data

int drm_writeback_connector_init(struct drm_device *dev, struct drm_writeback_connector *wb_connector, const struct drm_connector_funcs *con_funcs, const struct drm_encoder_helper_funcs *enc_helper_funcs, const u32 *formats, int n_formats, u32 possible_crtcs)¶: Initialize a writeback connector and its properties

Parameters

struct drm_device *dev: DRM device
struct drm_writeback_connector *wb_connector: Writeback connector to initialize
const struct drm_connector_funcs *con_funcs: Connector funcs vtable
const struct drm_encoder_helper_funcs *enc_helper_funcs: Encoder helper funcs vtable to be used by the internal encoder
const u32 *formats: Array of supported pixel formats for the writeback engine
int n_formats: Length of the formats array
u32 possible_crtcs: possible crtcs for the internal writeback encoder

Description

This function creates the writeback-connector-specific properties if they have not been already created, initializes the connector as type DRM_MODE_CONNECTOR_WRITEBACK, and correctly initializes the property values. It will also create an internal encoder associated with the drm_writeback_connector and set it to use the enc_helper_funcs vtable for the encoder helper.

Drivers should always use this function instead of drm_connector_init() to set up writeback connectors.

Return

0 on success, or a negative error code

int drm_writeback_connector_init_with_encoder(struct drm_device *dev, struct drm_writeback_connector *wb_connector, struct drm_encoder *enc, const struct drm_connector_funcs *con_funcs, const u32 *formats, int n_formats)¶: Initialize a writeback connector with a custom encoder

Parameters

struct drm_device *dev: DRM device
struct drm_writeback_connector *wb_connector: Writeback connector to initialize
struct drm_encoder *enc: handle to the already initialized drm encoder
const struct drm_connector_funcs *con_funcs: Connector funcs vtable
const u32 *formats: Array of supported pixel formats for the writeback engine
int n_formats: Length of the formats array

Description

This function creates the writeback-connector-specific properties if they have not been already created, initializes the connector as type DRM_MODE_CONNECTOR_WRITEBACK, and correctly initializes the property values.

This function assumes that the drm_writeback_connector’s encoder has already been created and initialized before invoking this function.

In addition, this function also assumes that callers of this API will manage assigning the encoder helper functions, possible_crtcs and any other encoder specific operation.

Drivers should always use this function instead of drm_connector_init() to set up writeback connectors if they want to manage themselves the lifetime of the associated encoder.

Return

0 on success, or a negative error code

void drm_writeback_queue_job(struct drm_writeback_connector *wb_connector, struct drm_connector_state *conn_state)¶: Queue a writeback job for later signalling

Parameters

struct drm_writeback_connector *wb_connector: The writeback connector to queue a job on
struct drm_connector_state *conn_state: The connector state containing the job to queue

Description

This function adds the job contained in conn_state to the job_queue for a writeback connector. It takes ownership of the writeback job and sets the conn_state->writeback_job to NULL, and so no access to the job may be performed by the caller after this function returns.

Drivers must ensure that for a given writeback connector, jobs are queued in exactly the same order as they will be completed by the hardware (and signaled via drm_writeback_signal_completion).

For every call to drm_writeback_queue_job() there must be exactly one call to drm_writeback_signal_completion()

void drm_writeback_signal_completion(struct drm_writeback_connector *wb_connector, int status)¶: Signal the completion of a writeback job

Parameters

struct drm_writeback_connector *wb_connector: The writeback connector whose job is complete
int status: Status code to set in the writeback out_fence (0 for success)

Description

Drivers should call this to signal the completion of a previously queued writeback job. It should be called as soon as possible after the hardware has finished writing, and may be called from interrupt context. It is the driver’s responsibility to ensure that for a given connector, the hardware completes writeback jobs in the same order as they are queued.

Unless the driver is holding its own reference to the framebuffer, it must not be accessed after calling this function.

Encoder Abstraction¶

Encoders represent the connecting element between the CRTC (as the overall pixel pipeline, represented by struct drm_crtc) and the connectors (as the generic sink entity, represented by struct drm_connector). An encoder takes pixel data from a CRTC and converts it to a format suitable for any attached connector. Encoders are objects exposed to userspace, originally to allow userspace to infer cloning and connector/CRTC restrictions. Unfortunately almost all drivers get this wrong, making the uabi pretty much useless. On top of that the exposed restrictions are too simple for today’s hardware, and the recommended way to infer restrictions is by using the DRM_MODE_ATOMIC_TEST_ONLY flag for the atomic IOCTL.

Otherwise encoders aren’t used in the uapi at all (any modeset request from userspace directly connects a connector with a CRTC), drivers are therefore free to use them however they wish. Modeset helper libraries make strong use of encoders to facilitate code sharing. But for more complex settings it is usually better to move shared code into a separate drm_bridge. Compared to encoders, bridges also have the benefit of being purely an internal abstraction since they are not exposed to userspace at all.

Encoders are initialized with drm_encoder_init() and cleaned up using drm_encoder_cleanup().

Encoder Functions Reference¶

struct drm_encoder_funcs¶: encoder controls

Definition

struct drm_encoder_funcs {
  void (*reset)(struct drm_encoder *encoder);
  void (*destroy)(struct drm_encoder *encoder);
  int (*late_register)(struct drm_encoder *encoder);
  void (*early_unregister)(struct drm_encoder *encoder);
};

Members

reset

Reset encoder hardware and software state to off. This function isn’t called by the core directly, only through drm_mode_config_reset(). It’s not a helper hook only for historical reasons.

destroy

Clean up encoder resources. This is only called at driver unload time through drm_mode_config_cleanup() since an encoder cannot be hotplugged in DRM.

late_register

This optional hook can be used to register additional userspace interfaces attached to the encoder like debugfs interfaces. It is called late in the driver load sequence from drm_dev_register(). Everything added from this callback should be unregistered in the early_unregister callback.

Returns:

0 on success, or a negative error code on failure.

early_unregister

This optional hook should be used to unregister the additional userspace interfaces attached to the encoder from late_register. It is called from drm_dev_unregister(), early in the driver unload sequence to disable userspace access before data structures are torndown.

Description

Encoders sit between CRTCs and connectors.

struct drm_encoder¶: central DRM encoder structure

Definition

struct drm_encoder {
  struct drm_device *dev;
  struct list_head head;
  struct drm_mode_object base;
  char *name;
  int encoder_type;
  unsigned index;
  uint32_t possible_crtcs;
  uint32_t possible_clones;
  struct drm_crtc *crtc;
  struct list_head bridge_chain;
  const struct drm_encoder_funcs *funcs;
  const struct drm_encoder_helper_funcs *helper_private;
};

Members

dev

parent DRM device

head

list management

base

base KMS object

name

human readable name, can be overwritten by the driver

encoder_type

One of the DRM_MODE_ENCODER_<foo> types in drm_mode.h. The following encoder types are defined thus far:

DRM_MODE_ENCODER_DAC for VGA and analog on DVI-I/DVI-A.
DRM_MODE_ENCODER_TMDS for DVI, HDMI and (embedded) DisplayPort.
DRM_MODE_ENCODER_LVDS for display panels, or in general any panel with a proprietary parallel connector.
DRM_MODE_ENCODER_TVDAC for TV output (Composite, S-Video, Component, SCART).
DRM_MODE_ENCODER_VIRTUAL for virtual machine displays
DRM_MODE_ENCODER_DSI for panels connected using the DSI serial bus.
DRM_MODE_ENCODER_DPI for panels connected using the DPI parallel bus.
DRM_MODE_ENCODER_DPMST for special fake encoders used to allow mutliple DP MST streams to share one physical encoder.

index

Position inside the mode_config.list, can be used as an array index. It is invariant over the lifetime of the encoder.

possible_crtcs

Bitmask of potential CRTC bindings, using drm_crtc_index() as the index into the bitfield. The driver must set the bits for all drm_crtc objects this encoder can be connected to before calling drm_dev_register().

You will get a WARN if you get this wrong in the driver.

Note that since CRTC objects can’t be hotplugged the assigned indices are stable and hence known before registering all objects.

possible_clones

Bitmask of potential sibling encoders for cloning, using drm_encoder_index() as the index into the bitfield. The driver must set the bits for all drm_encoder objects which can clone a drm_crtc together with this encoder before calling drm_dev_register(). Drivers should set the bit representing the encoder itself, too. Cloning bits should be set such that when two encoders can be used in a cloned configuration, they both should have each another bits set.

As an exception to the above rule if the driver doesn’t implement any cloning it can leave possible_clones set to 0. The core will automagically fix this up by setting the bit for the encoder itself.

You will get a WARN if you get this wrong in the driver.

Note that since encoder objects can’t be hotplugged the assigned indices are stable and hence known before registering all objects.

crtc

Currently bound CRTC, only really meaningful for non-atomic drivers. Atomic drivers should instead check drm_connector_state.crtc.

bridge_chain

Bridges attached to this encoder. Drivers shall not access this field directly.

funcs

control functions, can be NULL for simple managed encoders

helper_private

mid-layer private data

Description

CRTCs drive pixels to encoders, which convert them into signals appropriate for a given connector or set of connectors.

drmm_encoder_alloc¶

drmm_encoder_alloc (dev, type, member, funcs, encoder_type, name, ...)

Allocate and initialize an encoder

Parameters

dev: drm device
type: the type of the struct which contains struct drm_encoder
member: the name of the drm_encoder within type
funcs: callbacks for this encoder (optional)
encoder_type: user visible type of the encoder
name: printf style format string for the encoder name, or NULL for default name
...: variable arguments

Description

Allocates and initializes an encoder. Encoder should be subclassed as part of driver encoder objects. Cleanup is automatically handled through registering drm_encoder_cleanup() with drmm_add_action().

The drm_encoder_funcs.destroy hook must be NULL.

Return

Pointer to new encoder, or ERR_PTR on failure.

drmm_plain_encoder_alloc¶

drmm_plain_encoder_alloc (dev, funcs, encoder_type, name, ...)

Allocate and initialize an encoder

Parameters

dev: drm device
funcs: callbacks for this encoder (optional)
encoder_type: user visible type of the encoder
name: printf style format string for the encoder name, or NULL for default name
...: variable arguments

Description

This is a simplified version of drmm_encoder_alloc(), which only allocates and returns a struct drm_encoder instance, with no subclassing.

Return

Pointer to the new drm_encoder struct, or ERR_PTR on failure.

unsigned int drm_encoder_index(const struct drm_encoder *encoder)¶: find the index of a registered encoder

Parameters

const struct drm_encoder *encoder: encoder to find index for

Description

Given a registered encoder, return the index of that encoder within a DRM device’s list of encoders.

u32 drm_encoder_mask(const struct drm_encoder *encoder)¶: find the mask of a registered encoder

Parameters

const struct drm_encoder *encoder: encoder to find mask for

Description

Given a registered encoder, return the mask bit of that encoder for an encoder’s possible_clones field.

bool drm_encoder_crtc_ok(struct drm_encoder *encoder, struct drm_crtc *crtc)¶: can a given crtc drive a given encoder?

Parameters

struct drm_encoder *encoder: encoder to test
struct drm_crtc *crtc: crtc to test

Description

Returns false if encoder can’t be driven by crtc, true otherwise.

struct drm_encoder *drm_encoder_find(struct drm_device *dev, struct drm_file *file_priv, uint32_t id)¶: find a drm_encoder

Parameters

struct drm_device *dev: DRM device
struct drm_file *file_priv: drm file to check for lease against.
uint32_t id: encoder id

Description

Returns the encoder with id, NULL if it doesn’t exist. Simple wrapper around drm_mode_object_find().

drm_for_each_encoder_mask¶

drm_for_each_encoder_mask (encoder, dev, encoder_mask)

iterate over encoders specified by bitmask

Parameters

encoder: the loop cursor
dev: the DRM device
encoder_mask: bitmask of encoder indices

Description

Iterate over all encoders specified by bitmask.

drm_for_each_encoder¶

drm_for_each_encoder (encoder, dev)

iterate over all encoders

Parameters

encoder: the loop cursor
dev: the DRM device

Description

Iterate over all encoders of dev.

int drm_encoder_init(struct drm_device *dev, struct drm_encoder *encoder, const struct drm_encoder_funcs *funcs, int encoder_type, const char *name, ...)¶: Init a preallocated encoder

Parameters

struct drm_device *dev: drm device
struct drm_encoder *encoder: the encoder to init
const struct drm_encoder_funcs *funcs: callbacks for this encoder
int encoder_type: user visible type of the encoder
const char *name: printf style format string for the encoder name, or NULL for default name
...: variable arguments

Description

Initializes a preallocated encoder. Encoder should be subclassed as part of driver encoder objects. At driver unload time the driver’s drm_encoder_funcs.destroy hook should call drm_encoder_cleanup() and kfree() the encoder structure. The encoder structure should not be allocated with devm_kzalloc().

Note

consider using drmm_encoder_alloc() or drmm_encoder_init() instead of drm_encoder_init() to let the DRM managed resource infrastructure take care of cleanup and deallocation.

Return

Zero on success, error code on failure.

void drm_encoder_cleanup(struct drm_encoder *encoder)¶: cleans up an initialised encoder

Parameters

struct drm_encoder *encoder: encoder to cleanup

Description

Cleans up the encoder but doesn’t free the object.

int drmm_encoder_init(struct drm_device *dev, struct drm_encoder *encoder, const struct drm_encoder_funcs *funcs, int encoder_type, const char *name, ...)¶: Initialize a preallocated encoder

Parameters

struct drm_device *dev: drm device
struct drm_encoder *encoder: the encoder to init
const struct drm_encoder_funcs *funcs: callbacks for this encoder (optional)
int encoder_type: user visible type of the encoder
const char *name: printf style format string for the encoder name, or NULL for default name
...: variable arguments

Description

Initializes a preallocated encoder. Encoder should be subclassed as part of driver encoder objects. Cleanup is automatically handled through registering drm_encoder_cleanup() with drmm_add_action(). The encoder structure should be allocated with drmm_kzalloc().

The drm_encoder_funcs.destroy hook must be NULL.

Return

Zero on success, error code on failure.

KMS Locking¶

As KMS moves toward more fine grained locking, and atomic ioctl where userspace can indirectly control locking order, it becomes necessary to use ww_mutex and acquire-contexts to avoid deadlocks. But because the locking is more distributed around the driver code, we want a bit of extra utility/tracking out of our acquire-ctx. This is provided by struct drm_modeset_lock and struct drm_modeset_acquire_ctx.

For basic principles of ww_mutex, see: Wound/Wait Deadlock-Proof Mutex Design

The basic usage pattern is to:

drm_modeset_acquire_init(ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
retry:
foreach (lock in random_ordered_set_of_locks) {
    ret = drm_modeset_lock(lock, ctx)
    if (ret == -EDEADLK) {
        ret = drm_modeset_backoff(ctx);
        if (!ret)
            goto retry;
    }
    if (ret)
        goto out;
}
... do stuff ...
out:
drm_modeset_drop_locks(ctx);
drm_modeset_acquire_fini(ctx);

For convenience this control flow is implemented in DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() for the case where all modeset locks need to be taken through drm_modeset_lock_all_ctx().

If all that is needed is a single modeset lock, then the struct drm_modeset_acquire_ctx is not needed and the locking can be simplified by passing a NULL instead of ctx in the drm_modeset_lock() call or calling drm_modeset_lock_single_interruptible(). To unlock afterwards call drm_modeset_unlock().

On top of these per-object locks using ww_mutex there’s also an overall drm_mode_config.mutex, for protecting everything else. Mostly this means probe state of connectors, and preventing hotplug add/removal of connectors.

Finally there’s a bunch of dedicated locks to protect drm core internal lists and lookup data structures.

struct drm_modeset_acquire_ctx¶: locking context (see ww_acquire_ctx)

Definition

struct drm_modeset_acquire_ctx {
  struct ww_acquire_ctx ww_ctx;
  struct drm_modeset_lock *contended;
  depot_stack_handle_t stack_depot;
  struct list_head locked;
  bool trylock_only;
  bool interruptible;
};

Members

ww_ctx: base acquire ctx
contended: used internally for -EDEADLK handling
stack_depot: used internally for contention debugging
locked: list of held locks
trylock_only: trylock mode used in atomic contexts/panic notifiers
interruptible: whether interruptible locking should be used.

Description

Each thread competing for a set of locks must use one acquire ctx. And if any lock fxn returns -EDEADLK, it must backoff and retry.

struct drm_modeset_lock¶: used for locking modeset resources.

Definition

struct drm_modeset_lock {
  struct ww_mutex mutex;
  struct list_head head;
};

Members

mutex: resource locking
head: used to hold its place on drm_atomi_state.locked list when part of an atomic update

Description

Used for locking CRTCs and other modeset resources.

void drm_modeset_lock_fini(struct drm_modeset_lock *lock)¶: cleanup lock

Parameters

struct drm_modeset_lock *lock: lock to cleanup

bool drm_modeset_is_locked(struct drm_modeset_lock *lock)¶: equivalent to mutex_is_locked()

Parameters

struct drm_modeset_lock *lock: lock to check

void drm_modeset_lock_assert_held(struct drm_modeset_lock *lock)¶: equivalent to lockdep_assert_held()

Parameters

struct drm_modeset_lock *lock: lock to check

DRM_MODESET_LOCK_ALL_BEGIN¶

DRM_MODESET_LOCK_ALL_BEGIN (dev, ctx, flags, ret)

Helper to acquire modeset locks

Parameters

dev: drm device
ctx: local modeset acquire context, will be dereferenced
flags: DRM_MODESET_ACQUIRE_* flags to pass to drm_modeset_acquire_init()
ret: local ret/err/etc variable to track error status

Description

Use these macros to simplify grabbing all modeset locks using a local context. This has the advantage of reducing boilerplate, but also properly checking return values where appropriate.

Any code run between BEGIN and END will be holding the modeset locks.

This must be paired with DRM_MODESET_LOCK_ALL_END(). We will jump back and forth between the labels on deadlock and error conditions.

Drivers can acquire additional modeset locks. If any lock acquisition fails, the control flow needs to jump to DRM_MODESET_LOCK_ALL_END() with the ret parameter containing the return value of drm_modeset_lock().

Return

The only possible value of ret immediately after DRM_MODESET_LOCK_ALL_BEGIN() is 0, so no error checking is necessary

DRM_MODESET_LOCK_ALL_END¶

DRM_MODESET_LOCK_ALL_END (dev, ctx, ret)

Helper to release and cleanup modeset locks

Parameters

dev: drm device
ctx: local modeset acquire context, will be dereferenced
ret: local ret/err/etc variable to track error status

Description

The other side of DRM_MODESET_LOCK_ALL_BEGIN(). It will bounce back to BEGIN if ret is -EDEADLK.

It’s important that you use the same ret variable for begin and end so deadlock conditions are properly handled.

Return

ret will be untouched unless it is -EDEADLK on entry. That means that if you successfully acquire the locks, ret will be whatever your code sets it to. If there is a deadlock or other failure with acquire or backoff, ret will be set to that failure. In both of these cases the code between BEGIN/END will not be run, so the failure will reflect the inability to grab the locks.

void drm_modeset_lock_all(struct drm_device *dev)¶: take all modeset locks

Parameters

struct drm_device *dev: DRM device

Description

This function takes all modeset locks, suitable where a more fine-grained scheme isn’t (yet) implemented. Locks must be dropped by calling the drm_modeset_unlock_all() function.

This function is deprecated. It allocates a lock acquisition context and stores it in drm_device.mode_config. This facilitate conversion of existing code because it removes the need to manually deal with the acquisition context, but it is also brittle because the context is global and care must be taken not to nest calls. New code should use the drm_modeset_lock_all_ctx() function and pass in the context explicitly.

void drm_modeset_unlock_all(struct drm_device *dev)¶: drop all modeset locks

Parameters

struct drm_device *dev: DRM device

Description

This function drops all modeset locks taken by a previous call to the drm_modeset_lock_all() function.

This function is deprecated. It uses the lock acquisition context stored in drm_device.mode_config. This facilitates conversion of existing code because it removes the need to manually deal with the acquisition context, but it is also brittle because the context is global and care must be taken not to nest calls. New code should pass the acquisition context directly to the drm_modeset_drop_locks() function.

void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)¶: check that all modeset locks are locked

Parameters

struct drm_device *dev: device

Description

Useful as a debug assert.

void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx, uint32_t flags)¶: initialize acquire context

Parameters

struct drm_modeset_acquire_ctx *ctx: the acquire context
uint32_t flags: 0 or DRM_MODESET_ACQUIRE_INTERRUPTIBLE

Description

When passing DRM_MODESET_ACQUIRE_INTERRUPTIBLE to flags, all calls to drm_modeset_lock() will perform an interruptible wait.

void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)¶: cleanup acquire context

Parameters

struct drm_modeset_acquire_ctx *ctx: the acquire context

void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)¶: drop all locks

Parameters

struct drm_modeset_acquire_ctx *ctx: the acquire context

Description

Drop all locks currently held against this acquire context.

int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)¶: deadlock avoidance backoff

Parameters

struct drm_modeset_acquire_ctx *ctx: the acquire context

Description

If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), you must call this function to drop all currently held locks and block until the contended lock becomes available.

This function returns 0 on success, or -ERESTARTSYS if this context is initialized with DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the wait has been interrupted.

void drm_modeset_lock_init(struct drm_modeset_lock *lock)¶: initialize lock

Parameters

struct drm_modeset_lock *lock: lock to init

int drm_modeset_lock(struct drm_modeset_lock *lock, struct drm_modeset_acquire_ctx *ctx): take modeset lock

Parameters

struct drm_modeset_lock *lock: lock to take
struct drm_modeset_acquire_ctx *ctx: acquire ctx

Description

If ctx is not NULL, then its ww acquire context is used and the lock will be tracked by the context and can be released by calling drm_modeset_drop_locks(). If -EDEADLK is returned, this means a deadlock scenario has been detected and it is an error to attempt to take any more locks without first calling drm_modeset_backoff().

If the ctx is not NULL and initialized with DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with -ERESTARTSYS when interrupted.

If ctx is NULL then the function call behaves like a normal, uninterruptible non-nesting mutex_lock() call.

int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock)¶: take a single modeset lock

Parameters

struct drm_modeset_lock *lock: lock to take

Description

This function behaves as drm_modeset_lock() with a NULL context, but performs interruptible waits.

This function returns 0 on success, or -ERESTARTSYS when interrupted.

void drm_modeset_unlock(struct drm_modeset_lock *lock)¶: drop modeset lock

Parameters

struct drm_modeset_lock *lock: lock to release

int drm_modeset_lock_all_ctx(struct drm_device *dev, struct drm_modeset_acquire_ctx *ctx)¶: take all modeset locks

Parameters

struct drm_device *dev: DRM device
struct drm_modeset_acquire_ctx *ctx: lock acquisition context

Description

This function takes all modeset locks, suitable where a more fine-grained scheme isn’t (yet) implemented.

Unlike drm_modeset_lock_all(), it doesn’t take the drm_mode_config.mutex since that lock isn’t required for modeset state changes. Callers which need to grab that lock too need to do so outside of the acquire context ctx.

Locks acquired with this function should be released by calling the drm_modeset_drop_locks() function on ctx.

Return

0 on success or a negative error-code on failure.

KMS Properties¶

This section of the documentation is primarily aimed at user-space developers. For the driver APIs, see the other sections.

Requirements¶

KMS drivers might need to add extra properties to support new features. Each new property introduced in a driver needs to meet a few requirements, in addition to the one mentioned above:

It must be standardized, documenting:
- The full, exact, name string;
- If the property is an enum, all the valid value name strings;
- What values are accepted, and what these values mean;
- What the property does and how it can be used;
- How the property might interact with other, existing properties.
It must provide a generic helper in the core code to register that property on the object it attaches to.
Its content must be decoded by the core and provided in the object’s associated state structure. That includes anything drivers might want to precompute, like struct drm_clip_rect for planes.
Its initial state must match the behavior prior to the property introduction. This might be a fixed value matching what the hardware does, or it may be inherited from the state the firmware left the system in during boot.
An IGT test must be submitted where reasonable.

Property Types and Blob Property Support¶

Properties as represented by drm_property are used to extend the modeset interface exposed to userspace. For the atomic modeset IOCTL properties are even the only way to transport metadata about the desired new modeset configuration from userspace to the kernel. Properties have a well-defined value range, which is enforced by the drm core. See the documentation of the flags member of struct drm_property for an overview of the different property types and ranges.

Properties don’t store the current value directly, but need to be instantiated by attaching them to a drm_mode_object with drm_object_attach_property().

Property values are only 64bit. To support bigger piles of data (like gamma tables, color correction matrices or large structures) a property can instead point at a drm_property_blob with that additional data.

Properties are defined by their symbolic name, userspace must keep a per-object mapping from those names to the property ID used in the atomic IOCTL and in the get/set property IOCTL.

struct drm_property_enum¶: symbolic values for enumerations

Definition

struct drm_property_enum {
  uint64_t value;
  struct list_head head;
  char name[DRM_PROP_NAME_LEN];
};

Members

value

numeric property value for this enum entry

If the property has the type DRM_MODE_PROP_BITMASK, value stores a bitshift, not a bitmask. In other words, the enum entry is enabled if the bit number value is set in the property’s value. This enum entry has the bitmask 1 << value.

head

list of enum values, linked to drm_property.enum_list

name

symbolic name for the enum

Description

For enumeration and bitmask properties this structure stores the symbolic decoding for each value. This is used for example for the rotation property.

struct drm_property¶: modeset object property

Definition

struct drm_property {
  struct list_head head;
  struct drm_mode_object base;
  uint32_t flags;
  char name[DRM_PROP_NAME_LEN];
  uint32_t num_values;
  uint64_t *values;
  struct drm_device *dev;
  struct list_head enum_list;
};

Members

head

per-device list of properties, for cleanup.

base

base KMS object

flags

Property flags and type. A property needs to be one of the following types:

DRM_MODE_PROP_RANGE

Range properties report their minimum and maximum admissible unsigned values. The KMS core verifies that values set by application fit in that range. The range is unsigned. Range properties are created using drm_property_create_range().

DRM_MODE_PROP_SIGNED_RANGE

Range properties report their minimum and maximum admissible unsigned values. The KMS core verifies that values set by application fit in that range. The range is signed. Range properties are created using drm_property_create_signed_range().

DRM_MODE_PROP_ENUM

Enumerated properties take a numerical value that ranges from 0 to the number of enumerated values defined by the property minus one, and associate a free-formed string name to each value. Applications can retrieve the list of defined value-name pairs and use the numerical value to get and set property instance values. Enum properties are created using drm_property_create_enum().

DRM_MODE_PROP_BITMASK

Bitmask properties are enumeration properties that additionally restrict all enumerated values to the 0..63 range. Bitmask property instance values combine one or more of the enumerated bits defined by the property. Bitmask properties are created using drm_property_create_bitmask().

DRM_MODE_PROP_OBJECT

Object properties are used to link modeset objects. This is used extensively in the atomic support to create the display pipeline, by linking drm_framebuffer to drm_plane, drm_plane to drm_crtc and drm_connector to drm_crtc. An object property can only link to a specific type of drm_mode_object, this limit is enforced by the core. Object properties are created using drm_property_create_object().

Object properties work like blob properties, but in a more general fashion. They are limited to atomic drivers and must have the DRM_MODE_PROP_ATOMIC flag set.

DRM_MODE_PROP_BLOB

Blob properties store a binary blob without any format restriction. The binary blobs are created as KMS standalone objects, and blob property instance values store the ID of their associated blob object. Blob properties are created by calling drm_property_create() with DRM_MODE_PROP_BLOB as the type.

Actual blob objects to contain blob data are created using drm_property_create_blob(), or through the corresponding IOCTL.

Besides the built-in limit to only accept blob objects blob properties work exactly like object properties. The only reasons blob properties exist is backwards compatibility with existing userspace.

In addition a property can have any combination of the below flags:

DRM_MODE_PROP_ATOMIC: Set for properties which encode atomic modeset state. Such properties are not exposed to legacy userspace.
DRM_MODE_PROP_IMMUTABLE: Set for properties whose values cannot be changed by userspace. The kernel is allowed to update the value of these properties. This is generally used to expose probe state to userspace, e.g. the EDID, or the connector path property on DP MST sinks. Kernel can update the value of an immutable property by calling drm_object_property_set_value().

name

symbolic name of the properties

num_values

size of the values array.

values

Array with limits and values for the property. The interpretation of these limits is dependent upon the type per flags.

dev

DRM device

enum_list

List of drm_prop_enum_list structures with the symbolic names for enum and bitmask values.

Description

This structure represent a modeset object property. It combines both the name of the property with the set of permissible values. This means that when a driver wants to use a property with the same name on different objects, but with different value ranges, then it must create property for each one. An example would be rotation of drm_plane, when e.g. the primary plane cannot be rotated. But if both the name and the value range match, then the same property structure can be instantiated multiple times for the same object. Userspace must be able to cope with this and cannot assume that the same symbolic property will have the same modeset object ID on all modeset objects.

Properties are created by one of the special functions, as explained in detail in the flags structure member.

To actually expose a property it must be attached to each object using drm_object_attach_property(). Currently properties can only be attached to drm_connector, drm_crtc and drm_plane.

Properties are also used as the generic metadatatransport for the atomic IOCTL. Everything that was set directly in structures in the legacy modeset IOCTLs (like the plane source or destination windows, or e.g. the links to the CRTC) is exposed as a property with the DRM_MODE_PROP_ATOMIC flag set.

struct drm_property_blob¶: Blob data for drm_property

Definition

struct drm_property_blob {
  struct drm_mode_object base;
  struct drm_device *dev;
  struct list_head head_global;
  struct list_head head_file;
  size_t length;
  void *data;
};

Members

base: base KMS object
dev: DRM device
head_global: entry on the global blob list in drm_mode_config.property_blob_list.
head_file: entry on the per-file blob list in drm_file.blobs list.
length: size of the blob in bytes, invariant over the lifetime of the object
data: actual data, embedded at the end of this structure

Description

Blobs are used to store bigger values than what fits directly into the 64 bits available for a drm_property.

Blobs are reference counted using drm_property_blob_get() and drm_property_blob_put(). They are created using drm_property_create_blob().

bool drm_property_type_is(struct drm_property *property, uint32_t type)¶: check the type of a property

Parameters

struct drm_property *property: property to check
uint32_t type: property type to compare with

Description

This is a helper function becauase the uapi encoding of property types is a bit special for historical reasons.

struct drm_property *drm_property_find(struct drm_device *dev, struct drm_file *file_priv, uint32_t id)¶: find property object

Parameters

struct drm_device *dev: DRM device
struct drm_file *file_priv: drm file to check for lease against.
uint32_t id: property object id

Description

This function looks up the property object specified by id and returns it.

struct drm_property *drm_property_create(struct drm_device *dev, u32 flags, const char *name, int num_values)¶: create a new property type

Parameters

struct drm_device *dev: drm device
u32 flags: flags specifying the property type
const char *name: name of the property
int num_values: number of pre-defined values

Description

This creates a new generic drm property which can then be attached to a drm object with drm_object_attach_property(). The returned property object must be freed with drm_property_destroy(), which is done automatically when calling drm_mode_config_cleanup().

Return

A pointer to the newly created property on success, NULL on failure.

struct drm_property *drm_property_create_enum(struct drm_device *dev, u32 flags, const char *name, const struct drm_prop_enum_list *props, int num_values)¶: create a new enumeration property type

Parameters

struct drm_device *dev: drm device
u32 flags: flags specifying the property type
const char *name: name of the property
const struct drm_prop_enum_list *props: enumeration lists with property values
int num_values: number of pre-defined values

Description

This creates a new generic drm property which can then be attached to a drm object with drm_object_attach_property(). The returned property object must be freed with drm_property_destroy(), which is done automatically when calling drm_mode_config_cleanup().

Userspace is only allowed to set one of the predefined values for enumeration properties.

Return

A pointer to the newly created property on success, NULL on failure.

struct drm_property *drm_property_create_bitmask(struct drm_device *dev, u32 flags, const char *name, const struct drm_prop_enum_list *props, int num_props, uint64_t supported_bits)¶: create a new bitmask property type

Parameters

struct drm_device *dev: drm device
u32 flags: flags specifying the property type
const char *name: name of the property
const struct drm_prop_enum_list *props: enumeration lists with property bitflags
int num_props: size of the props array
uint64_t supported_bits: bitmask of all supported enumeration values

Description

This creates a new bitmask drm property which can then be attached to a drm object with drm_object_attach_property(). The returned property object must be freed with drm_property_destroy(), which is done automatically when calling drm_mode_config_cleanup().

Compared to plain enumeration properties userspace is allowed to set any or’ed together combination of the predefined property bitflag values

Return

A pointer to the newly created property on success, NULL on failure.

struct drm_property *drm_property_create_range(struct drm_device *dev, u32 flags, const char *name, uint64_t min, uint64_t max)¶: create a new unsigned ranged property type

Parameters

struct drm_device *dev: drm device
u32 flags: flags specifying the property type
const char *name: name of the property
uint64_t min: minimum value of the property
uint64_t max: maximum value of the property

Description

This creates a new generic drm property which can then be attached to a drm object with drm_object_attach_property(). The returned property object must be freed with drm_property_destroy(), which is done automatically when calling drm_mode_config_cleanup().

Userspace is allowed to set any unsigned integer value in the (min, max) range inclusive.

Return

A pointer to the newly created property on success, NULL on failure.

struct drm_property *drm_property_create_signed_range(struct drm_device *dev, u32 flags, const char *name, int64_t min, int64_t max)¶: create a new signed ranged property type

Parameters

struct drm_device *dev: drm device
u32 flags: flags specifying the property type
const char *name: name of the property
int64_t min: minimum value of the property
int64_t max: maximum value of the property

Description

This creates a new generic drm property which can then be attached to a drm object with drm_object_attach_property(). The returned property object must be freed with drm_property_destroy(), which is done automatically when calling drm_mode_config_cleanup().

Userspace is allowed to set any signed integer value in the (min, max) range inclusive.

Return

A pointer to the newly created property on success, NULL on failure.

struct drm_property *drm_property_create_object(struct drm_device *dev, u32 flags, const char *name, uint32_t type)¶: create a new object property type

Parameters

struct drm_device *dev: drm device
u32 flags: flags specifying the property type
const char *name: name of the property
uint32_t type: object type from DRM_MODE_OBJECT_* defines

Description

This creates a new generic drm property which can then be attached to a drm object with drm_object_attach_property(). The returned property object must be freed with drm_property_destroy(), which is done automatically when calling drm_mode_config_cleanup().

Userspace is only allowed to set this to any property value of the given type. Only useful for atomic properties, which is enforced.

Return

A pointer to the newly created property on success, NULL on failure.

struct drm_property *drm_property_create_bool(struct drm_device *dev, u32 flags, const char *name)¶: create a new boolean property type

Parameters

struct drm_device *dev: drm device
u32 flags: flags specifying the property type
const char *name: name of the property

Description

This creates a new generic drm property which can then be attached to a drm object with drm_object_attach_property(). The returned property object must be freed with drm_property_destroy(), which is done automatically when calling drm_mode_config_cleanup().

This is implemented as a ranged property with only {0, 1} as valid values.

Return

A pointer to the newly created property on success, NULL on failure.

int drm_property_add_enum(struct drm_property *property, uint64_t value, const char *name)¶: add a possible value to an enumeration property

Parameters

struct drm_property *property: enumeration property to change
uint64_t value: value of the new enumeration
const char *name: symbolic name of the new enumeration

Description

This functions adds enumerations to a property.

It’s use is deprecated, drivers should use one of the more specific helpers to directly create the property with all enumerations already attached.

Return

Zero on success, error code on failure.

void drm_property_destroy(struct drm_device *dev, struct drm_property *property)¶: destroy a drm property

Parameters

struct drm_device *dev: drm device
struct drm_property *property: property to destroy

Description

This function frees a property including any attached resources like enumeration values.

struct drm_property_blob *drm_property_create_blob(struct drm_device *dev, size_t length, const void *data)¶: Create new blob property

Parameters

struct drm_device *dev: DRM device to create property for
size_t length: Length to allocate for blob data
const void *data: If specified, copies data into blob

Description

Creates a new blob property for a specified DRM device, optionally copying data. Note that blob properties are meant to be invariant, hence the data must be filled out before the blob is used as the value of any property.

Return

New blob property with a single reference on success, or an ERR_PTR value on failure.

void drm_property_blob_put(struct drm_property_blob *blob)¶: release a blob property reference

Parameters

struct drm_property_blob *blob: DRM blob property

Description

Releases a reference to a blob property. May free the object.

struct drm_property_blob *drm_property_blob_get(struct drm_property_blob *blob)¶: acquire blob property reference

Parameters

struct drm_property_blob *blob: DRM blob property

Description

Acquires a reference to an existing blob property. Returns blob, which allows this to be used as a shorthand in assignments.

struct drm_property_blob *drm_property_lookup_blob(struct drm_device *dev, uint32_t id)¶: look up a blob property and take a reference

Parameters

struct drm_device *dev: drm device
uint32_t id: id of the blob property

Description

If successful, this takes an additional reference to the blob property. callers need to make sure to eventually unreferenced the returned property again, using drm_property_blob_put().

Return

NULL on failure, pointer to the blob on success.

int drm_property_replace_global_blob(struct drm_device *dev, struct drm_property_blob **replace, size_t length, const void *data, struct drm_mode_object *obj_holds_id, struct drm_property *prop_holds_id)¶: replace existing blob property

Parameters

struct drm_device *dev: drm device
struct drm_property_blob **replace: location of blob property pointer to be replaced
size_t length: length of data for new blob, or 0 for no data
const void *data: content for new blob, or NULL for no data
struct drm_mode_object *obj_holds_id: optional object for property holding blob ID
struct drm_property *prop_holds_id: optional property holding blob ID return 0 on success or error on failure

Description

This function will replace a global property in the blob list, optionally updating a property which holds the ID of that property.

If length is 0 or data is NULL, no new blob will be created, and the holding property, if specified, will be set to 0.

Access to the replace pointer is assumed to be protected by the caller, e.g. by holding the relevant modesetting object lock for its parent.

For example, a drm_connector has a ‘PATH’ property, which contains the ID of a blob property with the value of the MST path information. Calling this function with replace pointing to the connector’s path_blob_ptr, length and data set for the new path information, obj_holds_id set to the connector’s base object, and prop_holds_id set to the path property name, will perform a completely atomic update. The access to path_blob_ptr is protected by the caller holding a lock on the connector.

bool drm_property_replace_blob(struct drm_property_blob **blob, struct drm_property_blob *new_blob)¶: replace a blob property

Parameters

struct drm_property_blob **blob: a pointer to the member blob to be replaced
struct drm_property_blob *new_blob: the new blob to replace with

Return

true if the blob was in fact replaced.

Standard Connector Properties¶

DRM connectors have a few standardized properties:

EDID:

Blob property which contains the current EDID read from the sink. This is useful to parse sink identification information like vendor, model and serial. Drivers should update this property by calling drm_connector_update_edid_property(), usually after having parsed the EDID using drm_add_edid_modes(). Userspace cannot change this property.

User-space should not parse the EDID to obtain information exposed via other KMS properties (because the kernel might apply limits, quirks or fixups to the EDID). For instance, user-space should not try to parse mode lists from the EDID.

DPMS:

Legacy property for setting the power state of the connector. For atomic drivers this is only provided for backwards compatibility with existing drivers, it remaps to controlling the “ACTIVE” property on the CRTC the connector is linked to. Drivers should never set this property directly, it is handled by the DRM core by calling the drm_connector_funcs.dpms callback. For atomic drivers the remapping to the “ACTIVE” property is implemented in the DRM core.

Note that this property cannot be set through the MODE_ATOMIC ioctl, userspace must use “ACTIVE” on the CRTC instead.

WARNING:

For userspace also running on legacy drivers the “DPMS” semantics are a lot more complicated. First, userspace cannot rely on the “DPMS” value returned by the GETCONNECTOR actually reflecting reality, because many drivers fail to update it. For atomic drivers this is taken care of in drm_atomic_helper_update_legacy_modeset_state().

The second issue is that the DPMS state is only well-defined when the connector is connected to a CRTC. In atomic the DRM core enforces that “ACTIVE” is off in such a case, no such checks exists for “DPMS”.

Finally, when enabling an output using the legacy SETCONFIG ioctl then “DPMS” is forced to ON. But see above, that might not be reflected in the software value on legacy drivers.

Summarizing: Only set “DPMS” when the connector is known to be enabled, assume that a successful SETCONFIG call also sets “DPMS” to on, and never read back the value of “DPMS” because it can be incorrect.

PATH:

Connector path property to identify how this sink is physically connected. Used by DP MST. This should be set by calling drm_connector_set_path_property(), in the case of DP MST with the path property the MST manager created. Userspace cannot change this property.

TILE:

Connector tile group property to indicate how a set of DRM connector compose together into one logical screen. This is used by both high-res external screens (often only using a single cable, but exposing multiple DP MST sinks), or high-res integrated panels (like dual-link DSI) which are not gen-locked. Note that for tiled panels which are genlocked, like dual-link LVDS or dual-link DSI, the driver should try to not expose the tiling and virtualise both drm_crtc and drm_plane if needed. Drivers should update this value using drm_connector_set_tile_property(). Userspace cannot change this property.

link-status:

Connector link-status property to indicate the status of link. The default value of link-status is “GOOD”. If something fails during or after modeset, the kernel driver may set this to “BAD” and issue a hotplug uevent. Drivers should update this value using drm_connector_set_link_status_property().

When user-space receives the hotplug uevent and detects a “BAD” link-status, the sink doesn’t receive pixels anymore (e.g. the screen becomes completely black). The list of available modes may have changed. User-space is expected to pick a new mode if the current one has disappeared and perform a new modeset with link-status set to “GOOD” to re-enable the connector.

If multiple connectors share the same CRTC and one of them gets a “BAD” link-status, the other are unaffected (ie. the sinks still continue to receive pixels).

When user-space performs an atomic commit on a connector with a “BAD” link-status without resetting the property to “GOOD”, the sink may still not receive pixels. When user-space performs an atomic commit which resets the link-status property to “GOOD” without the ALLOW_MODESET flag set, it might fail because a modeset is required.

User-space can only change link-status to “GOOD”, changing it to “BAD” is a no-op.

For backwards compatibility with non-atomic userspace the kernel tries to automatically set the link-status back to “GOOD” in the SETCRTC IOCTL. This might fail if the mode is no longer valid, similar to how it might fail if a different screen has been connected in the interim.

non_desktop:

Indicates the output should be ignored for purposes of displaying a standard desktop environment or console. This is most likely because the output device is not rectilinear.

Content Protection:

This property is used by userspace to request the kernel protect future content communicated over the link. When requested, kernel will apply the appropriate means of protection (most often HDCP), and use the property to tell userspace the protection is active.

Drivers can set this up by calling drm_connector_attach_content_protection_property() on initialization.

The value of this property can be one of the following:

DRM_MODE_CONTENT_PROTECTION_UNDESIRED = 0: The link is not protected, content is transmitted in the clear.
DRM_MODE_CONTENT_PROTECTION_DESIRED = 1: Userspace has requested content protection, but the link is not currently protected. When in this state, kernel should enable Content Protection as soon as possible.
DRM_MODE_CONTENT_PROTECTION_ENABLED = 2: Userspace has requested content protection, and the link is protected. Only the driver can set the property to this value. If userspace attempts to set to ENABLED, kernel will return -EINVAL.

A few guidelines:

DESIRED state should be preserved until userspace de-asserts it by setting the property to UNDESIRED. This means ENABLED should only transition to UNDESIRED when the user explicitly requests it.
If the state is DESIRED, kernel should attempt to re-authenticate the link whenever possible. This includes across disable/enable, dpms, hotplug, downstream device changes, link status failures, etc..
Kernel sends uevent with the connector id and property id through drm_hdcp_update_content_protection, upon below kernel triggered scenarios:
- DESIRED -> ENABLED (authentication success)
- ENABLED -> DESIRED (termination of authentication)
Please note no uevents for userspace triggered property state changes, which can’t fail such as
- DESIRED/ENABLED -> UNDESIRED
- UNDESIRED -> DESIRED
Userspace is responsible for polling the property or listen to uevents to determine when the value transitions from ENABLED to DESIRED. This signifies the link is no longer protected and userspace should take appropriate action (whatever that might be).

HDCP Content Type:

This Enum property is used by the userspace to declare the content type of the display stream, to kernel. Here display stream stands for any display content that userspace intended to display through HDCP encryption.

Content Type of a stream is decided by the owner of the stream, as “HDCP Type0” or “HDCP Type1”.

The value of the property can be one of the below:

“HDCP Type0”: DRM_MODE_HDCP_CONTENT_TYPE0 = 0
“HDCP Type1”: DRM_MODE_HDCP_CONTENT_TYPE1 = 1

When kernel starts the HDCP authentication (see “Content Protection” for details), it uses the content type in “HDCP Content Type” for performing the HDCP authentication with the display sink.

Please note in HDCP spec versions, a link can be authenticated with HDCP 2.2 for Content Type 0/Content Type 1. Where as a link can be authenticated with HDCP1.4 only for Content Type 0(though it is implicit in nature. As there is no reference for Content Type in HDCP1.4).

HDCP2.2 authentication protocol itself takes the “Content Type” as a parameter, which is a input for the DP HDCP2.2 encryption algo.

In case of Type 0 content protection request, kernel driver can choose either of HDCP spec versions 1.4 and 2.2. When HDCP2.2 is used for “HDCP Type 0”, a HDCP 2.2 capable repeater in the downstream can send that content to a HDCP 1.4 authenticated HDCP sink (Type0 link). But if the content is classified as “HDCP Type 1”, above mentioned HDCP 2.2 repeater wont send the content to the HDCP sink as it can’t authenticate the HDCP1.4 capable sink for “HDCP Type 1”.

Please note userspace can be ignorant of the HDCP versions used by the kernel driver to achieve the “HDCP Content Type”.

At current scenario, classifying a content as Type 1 ensures that the content will be displayed only through the HDCP2.2 encrypted link.

Note that the HDCP Content Type property is introduced at HDCP 2.2, and defaults to type 0. It is only exposed by drivers supporting HDCP 2.2 (hence supporting Type 0 and Type 1). Based on how next versions of HDCP specs are defined content Type could be used for higher versions too.

If content type is changed when “Content Protection” is not UNDESIRED, then kernel will disable the HDCP and re-enable with new type in the same atomic commit. And when “Content Protection” is ENABLED, it means that link is HDCP authenticated and encrypted, for the transmission of the Type of stream mentioned at “HDCP Content Type”.

HDR_OUTPUT_METADATA:

Connector property to enable userspace to send HDR Metadata to driver. This metadata is based on the composition and blending policies decided by user, taking into account the hardware and sink capabilities. The driver gets this metadata and creates a Dynamic Range and Mastering Infoframe (DRM) in case of HDMI, SDP packet (Non-audio INFOFRAME SDP v1.3) for DP. This is then sent to sink. This notifies the sink of the upcoming frame’s Color Encoding and Luminance parameters.

Userspace first need to detect the HDR capabilities of sink by reading and parsing the EDID. Details of HDR metadata for HDMI are added in CTA 861.G spec. For DP , its defined in VESA DP Standard v1.4. It needs to then get the metadata information of the video/game/app content which are encoded in HDR (basically using HDR transfer functions). With this information it needs to decide on a blending policy and compose the relevant layers/overlays into a common format. Once this blending is done, userspace will be aware of the metadata of the composed frame to be send to sink. It then uses this property to communicate this metadata to driver which then make a Infoframe packet and sends to sink based on the type of encoder connected.

Userspace will be responsible to do Tone mapping operation in case:

Some layers are HDR and others are SDR
HDR layers luminance is not same as sink

It will even need to do colorspace conversion and get all layers to one common colorspace for blending. It can use either GL, Media or display engine to get this done based on the capabilities of the associated hardware.

Driver expects metadata to be put in struct hdr_output_metadata structure from userspace. This is received as blob and stored in drm_connector_state.hdr_output_metadata. It parses EDID and saves the sink metadata in struct hdr_sink_metadata, as drm_connector.hdr_sink_metadata. Driver uses drm_hdmi_infoframe_set_hdr_metadata() helper to set the HDR metadata, hdmi_drm_infoframe_pack() to pack the infoframe as per spec, in case of HDMI encoder.

max bpc:

This range property is used by userspace to limit the bit depth. When used the driver would limit the bpc in accordance with the valid range supported by the hardware and sink. Drivers to use the function drm_connector_attach_max_bpc_property() to create and attach the property to the connector during initialization.

Connectors also have one standardized atomic property:

CRTC_ID:: Mode object ID of the drm_crtc this connector should be connected to.

Connectors for LCD panels may also have one standardized property:

panel orientation:

On some devices the LCD panel is mounted in the casing in such a way that the up/top side of the panel does not match with the top side of the device. Userspace can use this property to check for this. Note that input coordinates from touchscreens (input devices with INPUT_PROP_DIRECT) will still map 1:1 to the actual LCD panel coordinates, so if userspace rotates the picture to adjust for the orientation it must also apply the same transformation to the touchscreen input coordinates. This property is initialized by calling drm_connector_set_panel_orientation() or drm_connector_set_panel_orientation_with_quirk()

scaling mode:

This property defines how a non-native mode is upscaled to the native mode of an LCD panel:

None:: No upscaling happens, scaling is left to the panel. Not all drivers expose this mode.
Full:: The output is upscaled to the full resolution of the panel, ignoring the aspect ratio.
Center:: No upscaling happens, the output is centered within the native resolution the panel.
Full aspect:: The output is upscaled to maximize either the width or height while retaining the aspect ratio.

This property should be set up by calling drm_connector_attach_scaling_mode_property(). Note that drivers can also expose this property to external outputs, in which case they must support “None”, which should be the default (since external screens have a built-in scaler).

subconnector:

This property is used by DVI-I, TVout and DisplayPort to indicate different connector subtypes. Enum values more or less match with those from main connector types. For DVI-I and TVout there is also a matching property “select subconnector” allowing to switch between signal types. DP subconnector corresponds to a downstream port.

privacy-screen sw-state, privacy-screen hw-state:

These 2 optional properties can be used to query the state of the electronic privacy screen that is available on some displays; and in some cases also control the state. If a driver implements these properties then both properties must be present.

“privacy-screen hw-state” is read-only and reflects the actual state of the privacy-screen, possible values: “Enabled”, “Disabled, “Enabled-locked”, “Disabled-locked”. The locked states indicate that the state cannot be changed through the DRM API. E.g. there might be devices where the firmware-setup options, or a hardware slider-switch, offer always on / off modes.

“privacy-screen sw-state” can be set to change the privacy-screen state when not locked. In this case the driver must update the hw-state property to reflect the new state on completion of the commit of the sw-state property. Setting the sw-state property when the hw-state is locked must be interpreted by the driver as a request to change the state to the set state when the hw-state becomes unlocked. E.g. if “privacy-screen hw-state” is “Enabled-locked” and the sw-state gets set to “Disabled” followed by the user unlocking the state by changing the slider-switch position, then the driver must set the state to “Disabled” upon receiving the unlock event.

In some cases the privacy-screen’s actual state might change outside of control of the DRM code. E.g. there might be a firmware handled hotkey which toggles the actual state, or the actual state might be changed through another userspace API such as writing /proc/acpi/ibm/lcdshadow. In this case the driver must update both the hw-state and the sw-state to reflect the new value, overwriting any pending state requests in the sw-state. Any pending sw-state requests are thus discarded.

Note that the ability for the state to change outside of control of the DRM master process means that userspace must not cache the value of the sw-state. Caching the sw-state value and including it in later atomic commits may lead to overriding a state change done through e.g. a firmware handled hotkey. Therefor userspace must not include the privacy-screen sw-state in an atomic commit unless it wants to change its value.

Colorspace:

This property helps select a suitable colorspace based on the sink capability. Modern sink devices support wider gamut like BT2020. This helps switch to BT2020 mode if the BT2020 encoded video stream is being played by the user, same for any other colorspace. Thereby giving a good visual experience to users.

The expectation from userspace is that it should parse the EDID and get supported colorspaces. Use this property and switch to the one supported. Sink supported colorspaces should be retrieved by userspace from EDID and driver will not explicitly expose them.

Basically the expectation from userspace is:

Set up CRTC DEGAMMA/CTM/GAMMA to convert to some sink colorspace
Set this new property to let the sink know what it converted the CRTC output to.
This property is just to inform sink what colorspace source is trying to drive.

Because between HDMI and DP have different colorspaces, drm_mode_create_hdmi_colorspace_property() is used for HDMI connector and drm_mode_create_dp_colorspace_property() is used for DP connector.

HDMI Specific Connector Properties¶

content type (HDMI specific):

Indicates content type setting to be used in HDMI infoframes to indicate content type for the external device, so that it adjusts its display settings accordingly.

The value of this property can be one of the following:

No Data:: Content type is unknown
Graphics:: Content type is graphics
Photo:: Content type is photo
Cinema:: Content type is cinema
Game:: Content type is game

The meaning of each content type is defined in CTA-861-G table 15.

Drivers can set up this property by calling drm_connector_attach_content_type_property(). Decoding to infoframe values is done through drm_hdmi_avi_infoframe_content_type().

Standard CRTC Properties¶

DRM CRTCs have a few standardized properties:

ACTIVE:

Atomic property for setting the power state of the CRTC. When set to 1 the CRTC will actively display content. When set to 0 the CRTC will be powered off. There is no expectation that user-space will reset CRTC resources like the mode and planes when setting ACTIVE to 0.

User-space can rely on an ACTIVE change to 1 to never fail an atomic test as long as no other property has changed. If a change to ACTIVE fails an atomic test, this is a driver bug. For this reason setting ACTIVE to 0 must not release internal resources (like reserved memory bandwidth or clock generators).

Note that the legacy DPMS property on connectors is internally routed to control this property for atomic drivers.

MODE_ID:

Atomic property for setting the CRTC display timings. The value is the ID of a blob containing the DRM mode info. To disable the CRTC, user-space must set this property to 0.

Setting MODE_ID to 0 will release reserved resources for the CRTC.

SCALING_FILTER:

Atomic property for setting the scaling filter for CRTC scaler

The value of this property can be one of the following:

Default:: Driver’s default scaling filter
Nearest Neighbor:: Nearest Neighbor scaling filter

Standard Plane Properties¶

DRM planes have a few standardized properties:

type:

Immutable property describing the type of the plane.

For user-space which has enabled the DRM_CLIENT_CAP_ATOMIC capability, the plane type is just a hint and is mostly superseded by atomic test-only commits. The type hint can still be used to come up more easily with a plane configuration accepted by the driver.

The value of this property can be one of the following:

“Primary”:

To light up a CRTC, attaching a primary plane is the most likely to work if it covers the whole CRTC and doesn’t have scaling or cropping set up.

Drivers may support more features for the primary plane, user-space can find out with test-only atomic commits.

Some primary planes are implicitly used by the kernel in the legacy IOCTLs DRM_IOCTL_MODE_SETCRTC and DRM_IOCTL_MODE_PAGE_FLIP. Therefore user-space must not mix explicit usage of any primary plane (e.g. through an atomic commit) with these legacy IOCTLs.

“Cursor”:

To enable this plane, using a framebuffer configured without scaling or cropping and with the following properties is the most likely to work:

If the driver provides the capabilities DRM_CAP_CURSOR_WIDTH and DRM_CAP_CURSOR_HEIGHT, create the framebuffer with this size. Otherwise, create a framebuffer with the size 64x64.
If the driver doesn’t support modifiers, create a framebuffer with a linear layout. Otherwise, use the IN_FORMATS plane property.

Drivers may support more features for the cursor plane, user-space can find out with test-only atomic commits.

Some cursor planes are implicitly used by the kernel in the legacy IOCTLs DRM_IOCTL_MODE_CURSOR and DRM_IOCTL_MODE_CURSOR2. Therefore user-space must not mix explicit usage of any cursor plane (e.g. through an atomic commit) with these legacy IOCTLs.

Some drivers may support cursors even if no cursor plane is exposed. In this case, the legacy cursor IOCTLs can be used to configure the cursor.

“Overlay”:

Neither primary nor cursor.

Overlay planes are the only planes exposed when the DRM_CLIENT_CAP_UNIVERSAL_PLANES capability is disabled.

IN_FORMATS:

Blob property which contains the set of buffer format and modifier pairs supported by this plane. The blob is a struct drm_format_modifier_blob. Without this property the plane doesn’t support buffers with modifiers. Userspace cannot change this property.

Note that userspace can check the DRM_CAP_ADDFB2_MODIFIERS driver capability for general modifier support. If this flag is set then every plane will have the IN_FORMATS property, even when it only supports DRM_FORMAT_MOD_LINEAR. Before linux kernel release v5.1 there have been various bugs in this area with inconsistencies between the capability flag and per-plane properties.

Plane Composition Properties¶

The basic plane composition model supported by standard plane properties only has a source rectangle (in logical pixels within the drm_framebuffer), with sub-pixel accuracy, which is scaled up to a pixel-aligned destination rectangle in the visible area of a drm_crtc. The visible area of a CRTC is defined by the horizontal and vertical visible pixels (stored in hdisplay and vdisplay) of the requested mode (stored in drm_crtc_state.mode). These two rectangles are both stored in the drm_plane_state.

For the atomic ioctl the following standard (atomic) properties on the plane object encode the basic plane composition model:

SRC_X:: X coordinate offset for the source rectangle within the drm_framebuffer, in 16.16 fixed point. Must be positive.
SRC_Y:: Y coordinate offset for the source rectangle within the drm_framebuffer, in 16.16 fixed point. Must be positive.
SRC_W:: Width for the source rectangle within the drm_framebuffer, in 16.16 fixed point. SRC_X plus SRC_W must be within the width of the source framebuffer. Must be positive.
SRC_H:: Height for the source rectangle within the drm_framebuffer, in 16.16 fixed point. SRC_Y plus SRC_H must be within the height of the source framebuffer. Must be positive.
CRTC_X:: X coordinate offset for the destination rectangle. Can be negative.
CRTC_Y:: Y coordinate offset for the destination rectangle. Can be negative.
CRTC_W:: Width for the destination rectangle. CRTC_X plus CRTC_W can extend past the currently visible horizontal area of the drm_crtc.
CRTC_H:: Height for the destination rectangle. CRTC_Y plus CRTC_H can extend past the currently visible vertical area of the drm_crtc.
FB_ID:: Mode object ID of the drm_framebuffer this plane should scan out.
CRTC_ID:: Mode object ID of the drm_crtc this plane should be connected to.

Note that the source rectangle must fully lie within the bounds of the drm_framebuffer. The destination rectangle can lie outside of the visible area of the current mode of the CRTC. It must be appropriately clipped by the driver, which can be done by calling drm_plane_helper_check_update(). Drivers are also allowed to round the subpixel sampling positions appropriately, but only to the next full pixel. No pixel outside of the source rectangle may ever be sampled, which is important when applying more sophisticated filtering than just a bilinear one when scaling. The filtering mode when scaling is unspecified.

On top of this basic transformation additional properties can be exposed by the driver:

alpha:

Alpha is setup with drm_plane_create_alpha_property(). It controls the plane-wide opacity, from transparent (0) to opaque (0xffff). It can be combined with pixel alpha. The pixel values in the framebuffers are expected to not be pre-multiplied by the global alpha associated to the plane.

rotation:

Rotation is set up with drm_plane_create_rotation_property(). It adds a rotation and reflection step between the source and destination rectangles. Without this property the rectangle is only scaled, but not rotated or reflected.

Possbile values:

“rotate-<degrees>”:: Signals that a drm plane is rotated <degrees> degrees in counter clockwise direction.
“reflect-<axis>”:: Signals that the contents of a drm plane is reflected along the <axis> axis, in the same way as mirroring.

reflect-x:

|o |    | o|
|  | -> |  |
| v|    |v |

reflect-y:

|o |    | ^|
|  | -> |  |
| v|    |o |

zpos:

Z position is set up with drm_plane_create_zpos_immutable_property() and drm_plane_create_zpos_property(). It controls the visibility of overlapping planes. Without this property the primary plane is always below the cursor plane, and ordering between all other planes is undefined. The positive Z axis points towards the user, i.e. planes with lower Z position values are underneath planes with higher Z position values. Two planes with the same Z position value have undefined ordering. Note that the Z position value can also be immutable, to inform userspace about the hard-coded stacking of planes, see drm_plane_create_zpos_immutable_property(). If any plane has a zpos property (either mutable or immutable), then all planes shall have a zpos property.

pixel blend mode:

Pixel blend mode is set up with drm_plane_create_blend_mode_property(). It adds a blend mode for alpha blending equation selection, describing how the pixels from the current plane are composited with the background.

Three alpha blending equations are defined:
“None”:
Blend formula that ignores the pixel alpha:
out.rgb = plane_alpha * fg.rgb +
        (1 - plane_alpha) * bg.rgb
“Pre-multiplied”:
Blend formula that assumes the pixel color values have been already pre-multiplied with the alpha channel values:
out.rgb = plane_alpha * fg.rgb +
        (1 - (plane_alpha * fg.alpha)) * bg.rgb
“Coverage”:
Blend formula that assumes the pixel color values have not been pre-multiplied and will do so when blending them to the background color values:
out.rgb = plane_alpha * fg.alpha * fg.rgb +
        (1 - (plane_alpha * fg.alpha)) * bg.rgb
Using the following symbols:

“fg.rgb”:
Each of the RGB component values from the plane’s pixel

“fg.alpha”:
Alpha component value from the plane’s pixel. If the plane’s pixel format has no alpha component, then this is assumed to be 1.0. In these cases, this property has no effect, as all three equations become equivalent.

“bg.rgb”:
Each of the RGB component values from the background

“plane_alpha”:
Plane alpha value set by the plane “alpha” property. If the plane does not expose the “alpha” property, then this is assumed to be 1.0

Note that all the property extensions described here apply either to the plane or the CRTC (e.g. for the background color, which currently is not exposed and assumed to be black).

SCALING_FILTER:

Indicates scaling filter to be used for plane scaler

The value of this property can be one of the following:

Default:: Driver’s default scaling filter
Nearest Neighbor:: Nearest Neighbor scaling filter

Drivers can set up this property for a plane by calling drm_plane_create_scaling_filter_property

Damage Tracking Properties¶

FB_DAMAGE_CLIPS is an optional plane property which provides a means to specify a list of damage rectangles on a plane in framebuffer coordinates of the framebuffer attached to the plane. In current context damage is the area of plane framebuffer that has changed since last plane update (also called page-flip), irrespective of whether currently attached framebuffer is same as framebuffer attached during last plane update or not.

FB_DAMAGE_CLIPS is a hint to kernel which could be helpful for some drivers to optimize internally especially for virtual devices where each framebuffer change needs to be transmitted over network, usb, etc.

Since FB_DAMAGE_CLIPS is a hint so it is an optional property. User-space can ignore damage clips property and in that case driver will do a full plane update. In case damage clips are provided then it is guaranteed that the area inside damage clips will be updated to plane. For efficiency driver can do full update or can update more than specified in damage clips. Since driver is free to read more, user-space must always render the entire visible framebuffer. Otherwise there can be corruptions. Also, if a user-space provides damage clips which doesn’t encompass the actual damage to framebuffer (since last plane update) can result in incorrect rendering.

FB_DAMAGE_CLIPS is a blob property with the layout of blob data is simply an array of drm_mode_rect. Unlike plane drm_plane_state.src coordinates, damage clips are not in 16.16 fixed point. Similar to plane src in framebuffer, damage clips cannot be negative. In damage clip, x1/y1 are inclusive and x2/y2 are exclusive. While kernel does not error for overlapped damage clips, it is strongly discouraged.

Drivers that are interested in damage interface for plane should enable FB_DAMAGE_CLIPS property by calling drm_plane_enable_fb_damage_clips(). Drivers implementing damage can use drm_atomic_helper_damage_iter_init() and drm_atomic_helper_damage_iter_next() helper iterator function to get damage rectangles clipped to drm_plane_state.src.

Color Management Properties¶

Color management or color space adjustments is supported through a set of 5 properties on the drm_crtc object. They are set up by calling drm_crtc_enable_color_mgmt().

“DEGAMMA_LUT”:

Blob property to set the degamma lookup table (LUT) mapping pixel data from the framebuffer before it is given to the transformation matrix. The data is interpreted as an array of struct drm_color_lut elements. Hardware might choose not to use the full precision of the LUT elements nor use all the elements of the LUT (for example the hardware might choose to interpolate between LUT[0] and LUT[4]).

Setting this to NULL (blob property value set to 0) means a linear/pass-thru gamma table should be used. This is generally the driver boot-up state too. Drivers can access this blob through drm_crtc_state.degamma_lut.

“DEGAMMA_LUT_SIZE”:

Unsinged range property to give the size of the lookup table to be set on the DEGAMMA_LUT property (the size depends on the underlying hardware). If drivers support multiple LUT sizes then they should publish the largest size, and sub-sample smaller sized LUTs (e.g. for split-gamma modes) appropriately.

“CTM”:

Blob property to set the current transformation matrix (CTM) apply to pixel data after the lookup through the degamma LUT and before the lookup through the gamma LUT. The data is interpreted as a struct drm_color_ctm.

Setting this to NULL (blob property value set to 0) means a unit/pass-thru matrix should be used. This is generally the driver boot-up state too. Drivers can access the blob for the color conversion matrix through drm_crtc_state.ctm.

“GAMMA_LUT”:

Blob property to set the gamma lookup table (LUT) mapping pixel data after the transformation matrix to data sent to the connector. The data is interpreted as an array of struct drm_color_lut elements. Hardware might choose not to use the full precision of the LUT elements nor use all the elements of the LUT (for example the hardware might choose to interpolate between LUT[0] and LUT[4]).

Setting this to NULL (blob property value set to 0) means a linear/pass-thru gamma table should be used. This is generally the driver boot-up state too. Drivers can access this blob through drm_crtc_state.gamma_lut.

Note that for mostly historical reasons stemming from Xorg heritage, this is also used to store the color map (also sometimes color lut, CLUT or color palette) for indexed formats like DRM_FORMAT_C8.

“GAMMA_LUT_SIZE”:

Unsigned range property to give the size of the lookup table to be set on the GAMMA_LUT property (the size depends on the underlying hardware). If drivers support multiple LUT sizes then they should publish the largest size, and sub-sample smaller sized LUTs (e.g. for split-gamma modes) appropriately.

There is also support for a legacy gamma table, which is set up by calling drm_mode_crtc_set_gamma_size(). The DRM core will then alias the legacy gamma ramp with “GAMMA_LUT” or, if that is unavailable, “DEGAMMA_LUT”.

Support for different non RGB color encodings is controlled through drm_plane specific COLOR_ENCODING and COLOR_RANGE properties. They are set up by calling drm_plane_create_color_properties().

“COLOR_ENCODING”:: Optional plane enum property to support different non RGB color encodings. The driver can provide a subset of standard enum values supported by the DRM plane.
“COLOR_RANGE”:: Optional plane enum property to support different non RGB color parameter ranges. The driver can provide a subset of standard enum values supported by the DRM plane.

Tile Group Property¶

Tile groups are used to represent tiled monitors with a unique integer identifier. Tiled monitors using DisplayID v1.3 have a unique 8-byte handle, we store this in a tile group, so we have a common identifier for all tiles in a monitor group. The property is called “TILE”. Drivers can manage tile groups using drm_mode_create_tile_group(), drm_mode_put_tile_group() and drm_mode_get_tile_group(). But this is only needed for internal panels where the tile group information is exposed through a non-standard way.

Explicit Fencing Properties¶

Explicit fencing allows userspace to control the buffer synchronization between devices. A Fence or a group of fences are transferred to/from userspace using Sync File fds and there are two DRM properties for that. IN_FENCE_FD on each DRM Plane to send fences to the kernel and OUT_FENCE_PTR on each DRM CRTC to receive fences from the kernel.

As a contrast, with implicit fencing the kernel keeps track of any ongoing rendering, and automatically ensures that the atomic update waits for any pending rendering to complete. This is usually tracked in struct dma_resv which can also contain mandatory kernel fences. Implicit syncing is how Linux traditionally worked (e.g. DRI2/3 on X.org), whereas explicit fencing is what Android wants.

“IN_FENCE_FD”:

Use this property to pass a fence that DRM should wait on before proceeding with the Atomic Commit request and show the framebuffer for the plane on the screen. The fence can be either a normal fence or a merged one, the sync_file framework will handle both cases and use a fence_array if a merged fence is received. Passing -1 here means no fences to wait on.

If the Atomic Commit request has the DRM_MODE_ATOMIC_TEST_ONLY flag it will only check if the Sync File is a valid one.

On the driver side the fence is stored on the fence parameter of struct drm_plane_state. Drivers which also support implicit fencing should extract the implicit fence using drm_gem_plane_helper_prepare_fb(), to make sure there’s consistent behaviour between drivers in precedence of implicit vs. explicit fencing.

“OUT_FENCE_PTR”:

Use this property to pass a file descriptor pointer to DRM. Once the Atomic Commit request call returns OUT_FENCE_PTR will be filled with the file descriptor number of a Sync File. This Sync File contains the CRTC fence that will be signaled when all framebuffers present on the Atomic Commit * request for that given CRTC are scanned out on the screen.

The Atomic Commit request fails if a invalid pointer is passed. If the Atomic Commit request fails for any other reason the out fence fd returned will be -1. On a Atomic Commit with the DRM_MODE_ATOMIC_TEST_ONLY flag the out fence will also be set to -1.

Note that out-fences don’t have a special interface to drivers and are internally represented by a struct drm_pending_vblank_event in struct drm_crtc_state, which is also used by the nonblocking atomic commit helpers and for the DRM event handling for existing userspace.

Variable Refresh Properties¶

Variable refresh rate capable displays can dynamically adjust their refresh rate by extending the duration of their vertical front porch until page flip or timeout occurs. This can reduce or remove stuttering and latency in scenarios where the page flip does not align with the vblank interval.

An example scenario would be an application flipping at a constant rate of 48Hz on a 60Hz display. The page flip will frequently miss the vblank interval and the same contents will be displayed twice. This can be observed as stuttering for content with motion.

If variable refresh rate was active on a display that supported a variable refresh range from 35Hz to 60Hz no stuttering would be observable for the example scenario. The minimum supported variable refresh rate of 35Hz is below the page flip frequency and the vertical front porch can be extended until the page flip occurs. The vblank interval will be directly aligned to the page flip rate.

Not all userspace content is suitable for use with variable refresh rate. Large and frequent changes in vertical front porch duration may worsen perceived stuttering for input sensitive applications.

Panel brightness will also vary with vertical front porch duration. Some panels may have noticeable differences in brightness between the minimum vertical front porch duration and the maximum vertical front porch duration. Large and frequent changes in vertical front porch duration may produce observable flickering for such panels.

Userspace control for variable refresh rate is supported via properties on the drm_connector and drm_crtc objects.

“vrr_capable”:

Optional drm_connector boolean property that drivers should attach with drm_connector_attach_vrr_capable_property() on connectors that could support variable refresh rates. Drivers should update the property value by calling drm_connector_set_vrr_capable_property().

Absence of the property should indicate absence of support.

“VRR_ENABLED”:

Default drm_crtc boolean property that notifies the driver that the content on the CRTC is suitable for variable refresh rate presentation. The driver will take this property as a hint to enable variable refresh rate support if the receiver supports it, ie. if the “vrr_capable” property is true on the drm_connector object. The vertical front porch duration will be extended until page-flip or timeout when enabled.

The minimum vertical front porch duration is defined as the vertical front porch duration for the current mode.

The maximum vertical front porch duration is greater than or equal to the minimum vertical front porch duration. The duration is derived from the minimum supported variable refresh rate for the connector.

The driver may place further restrictions within these minimum and maximum bounds.

Existing KMS Properties¶

The following table gives description of drm properties exposed by various modules/drivers. Because this table is very unwieldy, do not add any new properties here. Instead document them in a section above.

Owner Module/Drivers	Group	Property Name	Type	Property Values	Object attached	Description/Restrictions
	DVI-I	“subconnector”	ENUM	{ “Unknown”, “DVI-D”, “DVI-A” }	Connector	TBD
		“select subconnector”	ENUM	{ “Automatic”, “DVI-D”, “DVI-A” }	Connector	TBD
	TV	“subconnector”	ENUM	{ “Unknown”, “Composite”, “SVIDEO”, “Component”, “SCART” }	Connector	TBD
		“select subconnector”	ENUM	{ “Automatic”, “Composite”, “SVIDEO”, “Component”, “SCART” }	Connector	TBD
		“mode”	ENUM	{ “NTSC_M”, “NTSC_J”, “NTSC_443”, “PAL_B” } etc.	Connector	TBD
		“left margin”	RANGE	Min=0, Max=100	Connector	TBD
		“right margin”	RANGE	Min=0, Max=100	Connector	TBD
		“top margin”	RANGE	Min=0, Max=100	Connector	TBD
		“bottom margin”	RANGE	Min=0, Max=100	Connector	TBD
		“brightness”	RANGE	Min=0, Max=100	Connector	TBD
		“contrast”	RANGE	Min=0, Max=100	Connector	TBD
		“flicker reduction”	RANGE	Min=0, Max=100	Connector	TBD
		“overscan”	RANGE	Min=0, Max=100	Connector	TBD
		“saturation”	RANGE	Min=0, Max=100	Connector	TBD
		“hue”	RANGE	Min=0, Max=100	Connector	TBD
	Virtual GPU	“suggested X”	RANGE	Min=0, Max=0xffffffff	Connector	property to suggest an X offset for a connector
		“suggested Y”	RANGE	Min=0, Max=0xffffffff	Connector	property to suggest an Y offset for a connector
	Optional	“aspect ratio”	ENUM	{ “None”, “4:3”, “16:9” }	Connector	TDB
i915	Generic	“Broadcast RGB”	ENUM	{ “Automatic”, “Full”, “Limited 16:235” }	Connector	When this property is set to Limited 16:235 and CTM is set, the hardware will be programmed with the result of the multiplication of CTM by the limited range matrix to ensure the pixels normaly in the range 0..1.0 are remapped to the range 16/255..235/255.
		“audio”	ENUM	{ “force-dvi”, “off”, “auto”, “on” }	Connector	TBD
	SDVO-TV	“mode”	ENUM	{ “NTSC_M”, “NTSC_J”, “NTSC_443”, “PAL_B” } etc.	Connector	TBD
		“left_margin”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“right_margin”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“top_margin”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“bottom_margin”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“hpos”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“vpos”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“contrast”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“saturation”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“hue”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“sharpness”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“flicker_filter”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“flicker_filter_adaptive”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“flicker_filter_2d”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“tv_chroma_filter”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“tv_luma_filter”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“dot_crawl”	RANGE	Min=0, Max=1	Connector	TBD
	SDVO-TV/LVDS	“brightness”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
CDV gma-500	Generic	“Broadcast RGB”	ENUM	{ “Full”, “Limited 16:235” }	Connector	TBD
		“Broadcast RGB”	ENUM	{ “off”, “auto”, “on” }	Connector	TBD
Poulsbo	Generic	“backlight”	RANGE	Min=0, Max=100	Connector	TBD
	SDVO-TV	“mode”	ENUM	{ “NTSC_M”, “NTSC_J”, “NTSC_443”, “PAL_B” } etc.	Connector	TBD
		“left_margin”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“right_margin”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“top_margin”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“bottom_margin”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“hpos”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“vpos”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“contrast”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“saturation”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“hue”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“sharpness”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“flicker_filter”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“flicker_filter_adaptive”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“flicker_filter_2d”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“tv_chroma_filter”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“tv_luma_filter”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
		“dot_crawl”	RANGE	Min=0, Max=1	Connector	TBD
	SDVO-TV/LVDS	“brightness”	RANGE	Min=0, Max= SDVO dependent	Connector	TBD
armada	CRTC	“CSC_YUV”	ENUM	{ “Auto” , “CCIR601”, “CCIR709” }	CRTC	TBD
		“CSC_RGB”	ENUM	{ “Auto”, “Computer system”, “Studio” }	CRTC	TBD
	Overlay	“colorkey”	RANGE	Min=0, Max=0xffffff	Plane	TBD
		“colorkey_min”	RANGE	Min=0, Max=0xffffff	Plane	TBD
		“colorkey_max”	RANGE	Min=0, Max=0xffffff	Plane	TBD
		“colorkey_val”	RANGE	Min=0, Max=0xffffff	Plane	TBD
		“colorkey_alpha”	RANGE	Min=0, Max=0xffffff	Plane	TBD
		“colorkey_mode”	ENUM	{ “disabled”, “Y component”, “U component” , “V component”, “RGB”, “R component”, “G component”, “B component” }	Plane	TBD
		“brightness”	RANGE	Min=0, Max=256 + 255	Plane	TBD
		“contrast”	RANGE	Min=0, Max=0x7fff	Plane	TBD
		“saturation”	RANGE	Min=0, Max=0x7fff	Plane	TBD
exynos	CRTC	“mode”	ENUM	{ “normal”, “blank” }	CRTC	TBD
i2c/ch7006_drv	Generic	“scale”	RANGE	Min=0, Max=2	Connector	TBD
	TV	“mode”	ENUM	{ “PAL”, “PAL-M”,”PAL-N”}, ”PAL-Nc” , “PAL-60”, “NTSC-M”, “NTSC-J” }	Connector	TBD
nouveau	NV10 Overlay	“colorkey”	RANGE	Min=0, Max=0x01ffffff	Plane	TBD
		“contrast”	RANGE	Min=0, Max=8192-1	Plane	TBD
		“brightness”	RANGE	Min=0, Max=1024	Plane	TBD
		“hue”	RANGE	Min=0, Max=359	Plane	TBD
		“saturation”	RANGE	Min=0, Max=8192-1	Plane	TBD
		“iturbt_709”	RANGE	Min=0, Max=1	Plane	TBD
	Nv04 Overlay	“colorkey”	RANGE	Min=0, Max=0x01ffffff	Plane	TBD
		“brightness”	RANGE	Min=0, Max=1024	Plane	TBD
	Display	“dithering mode”	ENUM	{ “auto”, “off”, “on” }	Connector	TBD
		“dithering depth”	ENUM	{ “auto”, “off”, “on”, “static 2x2”, “dynamic 2x2”, “temporal” }	Connector	TBD
		“underscan”	ENUM	{ “auto”, “6 bpc”, “8 bpc” }	Connector	TBD
		“underscan hborder”	RANGE	Min=0, Max=128	Connector	TBD
		“underscan vborder”	RANGE	Min=0, Max=128	Connector	TBD
		“vibrant hue”	RANGE	Min=0, Max=180	Connector	TBD
		“color vibrance”	RANGE	Min=0, Max=200	Connector	TBD
omap	Generic	“zorder”	RANGE	Min=0, Max=3	CRTC, Plane	TBD
qxl	Generic	“hotplug_mode_update”	RANGE	Min=0, Max=1	Connector	TBD
radeon	DVI-I	“coherent”	RANGE	Min=0, Max=1	Connector	TBD
	DAC enable load detect	“load detection”	RANGE	Min=0, Max=1	Connector	TBD
	TV Standard	“tv standard”	ENUM	{ “ntsc”, “pal”, “pal-m”, “pal-60”, “ntsc-j” , “scart-pal”, “pal-cn”, “secam” }	Connector	TBD
	legacy TMDS PLL detect	“tmds_pll”	ENUM	{ “driver”, “bios” }		TBD
	Underscan	“underscan”	ENUM	{ “off”, “on”, “auto” }	Connector	TBD
		“underscan hborder”	RANGE	Min=0, Max=128	Connector	TBD
		“underscan vborder”	RANGE	Min=0, Max=128	Connector	TBD
	Audio	“audio”	ENUM	{ “off”, “on”, “auto” }	Connector	TBD
	FMT Dithering	“dither”	ENUM	{ “off”, “on” }	Connector	TBD
		“colorkey”	RANGE	Min=0, Max=0x01ffffff	Plane	TBD

Vertical Blanking¶

From the computer’s perspective, every time the monitor displays a new frame the scanout engine has “scanned out” the display image from top to bottom, one row of pixels at a time. The current row of pixels is referred to as the current scanline.

In addition to the display’s visible area, there’s usually a couple of extra scanlines which aren’t actually displayed on the screen. These extra scanlines don’t contain image data and are occasionally used for features like audio and infoframes. The region made up of these scanlines is referred to as the vertical blanking region, or vblank for short.

For historical reference, the vertical blanking period was designed to give the electron gun (on CRTs) enough time to move back to the top of the screen to start scanning out the next frame. Similar for horizontal blanking periods. They were designed to give the electron gun enough time to move back to the other side of the screen to start scanning the next scanline.

physical →   ⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽
top of      |                                        |
display     |                                        |
            |               New frame                |
            |                                        |
            |↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓|
            |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| ← Scanline,
            |↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓|   updates the
            |                                        |   frame as it
            |                                        |   travels down
            |                                        |   ("scan out")
            |               Old frame                |
            |                                        |
            |                                        |
            |                                        |
            |                                        |   physical
            |                                        |   bottom of
vertical    |⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽| ← display
blanking    ┆xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx┆
region   →  ┆xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx┆
            ┆xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx┆
start of →   ⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽
new frame

“Physical top of display” is the reference point for the high-precision/ corrected timestamp.

On a lot of display hardware, programming needs to take effect during the vertical blanking period so that settings like gamma, the image buffer buffer to be scanned out, etc. can safely be changed without showing any visual artifacts on the screen. In some unforgiving hardware, some of this programming has to both start and end in the same vblank. To help with the timing of the hardware programming, an interrupt is usually available to notify the driver when it can start the updating of registers. The interrupt is in this context named the vblank interrupt.

The vblank interrupt may be fired at different points depending on the hardware. Some hardware implementations will fire the interrupt when the new frame start, other implementations will fire the interrupt at different points in time.

Vertical blanking plays a major role in graphics rendering. To achieve tear-free display, users must synchronize page flips and/or rendering to vertical blanking. The DRM API offers ioctls to perform page flips synchronized to vertical blanking and wait for vertical blanking.

The DRM core handles most of the vertical blanking management logic, which involves filtering out spurious interrupts, keeping race-free blanking counters, coping with counter wrap-around and resets and keeping use counts. It relies on the driver to generate vertical blanking interrupts and optionally provide a hardware vertical blanking counter.

Drivers must initialize the vertical blanking handling core with a call to drm_vblank_init(). Minimally, a driver needs to implement drm_crtc_funcs.enable_vblank and drm_crtc_funcs.disable_vblank plus call drm_crtc_handle_vblank() in its vblank interrupt handler for working vblank support.

Vertical blanking interrupts can be enabled by the DRM core or by drivers themselves (for instance to handle page flipping operations). The DRM core maintains a vertical blanking use count to ensure that the interrupts are not disabled while a user still needs them. To increment the use count, drivers call drm_crtc_vblank_get() and release the vblank reference again with drm_crtc_vblank_put(). In between these two calls vblank interrupts are guaranteed to be enabled.

On many hardware disabling the vblank interrupt cannot be done in a race-free manner, see drm_driver.vblank_disable_immediate and drm_driver.max_vblank_count. In that case the vblank core only disables the vblanks after a timer has expired, which can be configured through the vblankoffdelay module parameter.

Drivers for hardware without support for vertical-blanking interrupts must not call drm_vblank_init(). For such drivers, atomic helpers will automatically generate fake vblank events as part of the display update. This functionality also can be controlled by the driver by enabling and disabling struct drm_crtc_state.no_vblank.

Vertical Blanking and Interrupt Handling Functions Reference¶

struct drm_pending_vblank_event¶: pending vblank event tracking

Definition

struct drm_pending_vblank_event {
  struct drm_pending_event base;
  unsigned int pipe;
  u64 sequence;
  union {
    struct drm_event base;
    struct drm_event_vblank vbl;
    struct drm_event_crtc_sequence seq;
  } event;
};

Members

base: Base structure for tracking pending DRM events.
pipe: drm_crtc_index() of the drm_crtc this event is for.
sequence: frame event should be triggered at
event: Actual event which will be sent to userspace.
event.base: DRM event base class.
event.vbl: Event payload for vblank events, requested through either the MODE_PAGE_FLIP or MODE_ATOMIC IOCTL. Also generated by the legacy WAIT_VBLANK IOCTL, but new userspace should use MODE_QUEUE_SEQUENCE and event.seq instead.
event.seq: Event payload for the MODE_QUEUEU_SEQUENCE IOCTL.

struct drm_vblank_crtc¶: vblank tracking for a CRTC

Definition

struct drm_vblank_crtc {
  struct drm_device *dev;
  wait_queue_head_t queue;
  struct timer_list disable_timer;
  seqlock_t seqlock;
  atomic64_t count;
  ktime_t time;
  atomic_t refcount;
  u32 last;
  u32 max_vblank_count;
  unsigned int inmodeset;
  unsigned int pipe;
  int framedur_ns;
  int linedur_ns;
  struct drm_display_mode hwmode;
  bool enabled;
  struct kthread_worker *worker;
  struct list_head pending_work;
  wait_queue_head_t work_wait_queue;
};

Members

dev

Pointer to the drm_device.

queue

Wait queue for vblank waiters.

disable_timer

Disable timer for the delayed vblank disabling hysteresis logic. Vblank disabling is controlled through the drm_vblank_offdelay module option and the setting of the drm_device.max_vblank_count value.

seqlock

Protect vblank count and time.

count

Current software vblank counter.

Note that for a given vblank counter value drm_crtc_handle_vblank() and drm_crtc_vblank_count() or drm_crtc_vblank_count_and_time() provide a barrier: Any writes done before calling drm_crtc_handle_vblank() will be visible to callers of the later functions, iff the vblank count is the same or a later one.

IMPORTANT: This guarantee requires barriers, therefor never access this field directly. Use drm_crtc_vblank_count() instead.

time

Vblank timestamp corresponding to count.

refcount

Number of users/waiters of the vblank interrupt. Only when this refcount reaches 0 can the hardware interrupt be disabled using disable_timer.

last

Protected by drm_device.vbl_lock, used for wraparound handling.

max_vblank_count

Maximum value of the vblank registers for this crtc. This value +1 will result in a wrap-around of the vblank register. It is used by the vblank core to handle wrap-arounds.

If set to zero the vblank core will try to guess the elapsed vblanks between times when the vblank interrupt is disabled through high-precision timestamps. That approach is suffering from small races and imprecision over longer time periods, hence exposing a hardware vblank counter is always recommended.

This is the runtime configurable per-crtc maximum set through drm_crtc_set_max_vblank_count(). If this is used the driver must leave the device wide drm_device.max_vblank_count at zero.

If non-zero, drm_crtc_funcs.get_vblank_counter must be set.

inmodeset

Tracks whether the vblank is disabled due to a modeset. For legacy driver bit 2 additionally tracks whether an additional temporary vblank reference has been acquired to paper over the hardware counter resetting/jumping. KMS drivers should instead just call drm_crtc_vblank_off() and drm_crtc_vblank_on(), which explicitly save and restore the vblank count.

pipe

drm_crtc_index() of the drm_crtc corresponding to this structure.

framedur_ns

Frame/Field duration in ns, used by drm_crtc_vblank_helper_get_vblank_timestamp() and computed by drm_calc_timestamping_constants().

linedur_ns

Line duration in ns, used by drm_crtc_vblank_helper_get_vblank_timestamp() and computed by drm_calc_timestamping_constants().

hwmode

Cache of the current hardware display mode. Only valid when enabled is set. This is used by helpers like drm_crtc_vblank_helper_get_vblank_timestamp(). We can’t just access the hardware mode by e.g. looking at drm_crtc_state.adjusted_mode, because that one is really hard to get from interrupt context.

enabled

Tracks the enabling state of the corresponding drm_crtc to avoid double-disabling and hence corrupting saved state. Needed by drivers not using atomic KMS, since those might go through their CRTC disabling functions multiple times.

worker

The kthread_worker used for executing vblank works.

pending_work

A list of scheduled drm_vblank_work items that are waiting for a future vblank.

work_wait_queue

The wait queue used for signaling that a drm_vblank_work item has either finished executing, or was cancelled.

Description

This structure tracks the vblank state for one CRTC.

Note that for historical reasons - the vblank handling code is still shared with legacy/non-kms drivers - this is a free-standing structure not directly connected to struct drm_crtc. But all public interface functions are taking a struct drm_crtc to hide this implementation detail.

u64 drm_crtc_accurate_vblank_count(struct drm_crtc *crtc)¶: retrieve the master vblank counter

Parameters

struct drm_crtc *crtc: which counter to retrieve

Description

This function is similar to drm_crtc_vblank_count() but this function interpolates to handle a race with vblank interrupts using the high precision timestamping support.

This is mostly useful for hardware that can obtain the scanout position, but doesn’t have a hardware frame counter.

int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs)¶: initialize vblank support

Parameters

struct drm_device *dev: DRM device
unsigned int num_crtcs: number of CRTCs supported by dev

Description

This function initializes vblank support for num_crtcs display pipelines. Cleanup is handled automatically through a cleanup function added with drmm_add_action_or_reset().

Return

Zero on success or a negative error code on failure.

bool drm_dev_has_vblank(const struct drm_device *dev)¶: test if vblanking has been initialized for a device

Parameters

const struct drm_device *dev: the device

Description

Drivers may call this function to test if vblank support is initialized for a device. For most hardware this means that vblanking can also be enabled.

Atomic helpers use this function to initialize drm_crtc_state.no_vblank. See also drm_atomic_helper_check_modeset().

Return

True if vblanking has been initialized for the given device, false otherwise.

wait_queue_head_t *drm_crtc_vblank_waitqueue(struct drm_crtc *crtc)¶: get vblank waitqueue for the CRTC

Parameters

struct drm_crtc *crtc: which CRTC’s vblank waitqueue to retrieve

Description

This function returns a pointer to the vblank waitqueue for the CRTC. Drivers can use this to implement vblank waits using wait_event() and related functions.

void drm_calc_timestamping_constants(struct drm_crtc *crtc, const struct drm_display_mode *mode)¶: calculate vblank timestamp constants

Parameters

struct drm_crtc *crtc: drm_crtc whose timestamp constants should be updated.
const struct drm_display_mode *mode: display mode containing the scanout timings

Description

Calculate and store various constants which are later needed by vblank and swap-completion timestamping, e.g, by drm_crtc_vblank_helper_get_vblank_timestamp(). They are derived from CRTC’s true scanout timing, so they take things like panel scaling or other adjustments into account.

bool drm_crtc_vblank_helper_get_vblank_timestamp_internal(struct drm_crtc *crtc, int *max_error, ktime_t *vblank_time, bool in_vblank_irq, drm_vblank_get_scanout_position_func get_scanout_position)¶: precise vblank timestamp helper

Parameters

struct drm_crtc *crtc: CRTC whose vblank timestamp to retrieve
int *max_error: Desired maximum allowable error in timestamps (nanosecs) On return contains true maximum error of timestamp
ktime_t *vblank_time: Pointer to time which should receive the timestamp

bool in_vblank_irq

True when called from drm_crtc_handle_vblank(). Some drivers need to apply some workarounds for gpu-specific vblank irq quirks if flag is set.

drm_vblank_get_scanout_position_func get_scanout_position

Callback function to retrieve the scanout position. See struct drm_crtc_helper_funcs.get_scanout_position.

Description

Implements calculation of exact vblank timestamps from given drm_display_mode timings and current video scanout position of a CRTC.

The current implementation only handles standard video modes. For double scan and interlaced modes the driver is supposed to adjust the hardware mode (taken from drm_crtc_state.adjusted mode for atomic modeset drivers) to match the scanout position reported.

Note that atomic drivers must call drm_calc_timestamping_constants() before enabling a CRTC. The atomic helpers already take care of that in drm_atomic_helper_calc_timestamping_constants().

Returns true on success, and false on failure, i.e. when no accurate timestamp could be acquired.

Return

bool drm_crtc_vblank_helper_get_vblank_timestamp(struct drm_crtc *crtc, int *max_error, ktime_t *vblank_time, bool in_vblank_irq)¶: precise vblank timestamp helper

Parameters

struct drm_crtc *crtc: CRTC whose vblank timestamp to retrieve
int *max_error: Desired maximum allowable error in timestamps (nanosecs) On return contains true maximum error of timestamp
ktime_t *vblank_time: Pointer to time which should receive the timestamp

bool in_vblank_irq

True when called from drm_crtc_handle_vblank(). Some drivers need to apply some workarounds for gpu-specific vblank irq quirks if flag is set.

Description

Implements calculation of exact vblank timestamps from given drm_display_mode timings and current video scanout position of a CRTC. This can be directly used as the drm_crtc_funcs.get_vblank_timestamp implementation of a kms driver if drm_crtc_helper_funcs.get_scanout_position is implemented.

The current implementation only handles standard video modes. For double scan and interlaced modes the driver is supposed to adjust the hardware mode (taken from drm_crtc_state.adjusted mode for atomic modeset drivers) to match the scanout position reported.

Note that atomic drivers must call drm_calc_timestamping_constants() before enabling a CRTC. The atomic helpers already take care of that in drm_atomic_helper_calc_timestamping_constants().

Returns true on success, and false on failure, i.e. when no accurate timestamp could be acquired.

Return

u64 drm_crtc_vblank_count(struct drm_crtc *crtc)¶: retrieve “cooked” vblank counter value

Parameters

struct drm_crtc *crtc: which counter to retrieve

Description

Fetches the “cooked” vblank count value that represents the number of vblank events since the system was booted, including lost events due to modesetting activity. Note that this timer isn’t correct against a racing vblank interrupt (since it only reports the software vblank counter), see drm_crtc_accurate_vblank_count() for such use-cases.

Note that for a given vblank counter value drm_crtc_handle_vblank() and drm_crtc_vblank_count() or drm_crtc_vblank_count_and_time() provide a barrier: Any writes done before calling drm_crtc_handle_vblank() will be visible to callers of the later functions, if the vblank count is the same or a later one.

Vertical Blank Work¶

Many DRM drivers need to program hardware in a time-sensitive manner, many times with a deadline of starting and finishing within a certain region of the scanout. Most of the time the safest way to accomplish this is to simply do said time-sensitive programming in the driver’s IRQ handler, which allows drivers to avoid being preempted during these critical regions. Or even better, the hardware may even handle applying such time-critical programming independently of the CPU.

While there’s a decent amount of hardware that’s designed so that the CPU doesn’t need to be concerned with extremely time-sensitive programming, there’s a few situations where it can’t be helped. Some unforgiving hardware may require that certain time-sensitive programming be handled completely by the CPU, and said programming may even take too long to handle in an IRQ handler. Another such situation would be where the driver needs to perform a task that needs to complete within a specific scanout period, but might possibly block and thus cannot be handled in an IRQ context. Both of these situations can’t be solved perfectly in Linux since we’re not a realtime kernel, and thus the scheduler may cause us to miss our deadline if it decides to preempt us. But for some drivers, it’s good enough if we can lower our chance of being preempted to an absolute minimum.

This is where drm_vblank_work comes in. drm_vblank_work provides a simple generic delayed work implementation which delays work execution until a particular vblank has passed, and then executes the work at realtime priority. This provides the best possible chance at performing time-sensitive hardware programming on time, even when the system is under heavy load. drm_vblank_work also supports rescheduling, so that self re-arming work items can be easily implemented.

Vertical Blank Work Functions Reference¶

struct drm_vblank_work¶: A delayed work item which delays until a target vblank passes, and then executes at realtime priority outside of IRQ context.

Definition

struct drm_vblank_work {
  struct kthread_work base;
  struct drm_vblank_crtc *vblank;
  u64 count;
  int cancelling;
  struct list_head node;
};

Members

base: The base kthread_work item which will be executed by drm_vblank_crtc.worker. Drivers should not interact with this directly, and instead rely on drm_vblank_work_init() to initialize this.
vblank: A pointer to drm_vblank_crtc this work item belongs to.
count: The target vblank this work will execute on. Drivers should not modify this value directly, and instead use drm_vblank_work_schedule()
cancelling: The number of drm_vblank_work_cancel_sync() calls that are currently running. A work item cannot be rescheduled until all calls have finished.
node: The position of this work item in drm_vblank_crtc.pending_work.

Description

to_drm_vblank_work¶

to_drm_vblank_work (_work)

Retrieve the respective drm_vblank_work item from a kthread_work

Parameters

_work: The kthread_work embedded inside a drm_vblank_work

int drm_vblank_work_schedule(struct drm_vblank_work *work, u64 count, bool nextonmiss)¶: schedule a vblank work

Parameters

struct drm_vblank_work *work: vblank work to schedule
u64 count: target vblank count
bool nextonmiss: defer until the next vblank if target vblank was missed

Description

Schedule work for execution once the crtc vblank count reaches count.

If the crtc vblank count has already reached count and nextonmiss is false the work starts to execute immediately.

If the crtc vblank count has already reached count and nextonmiss is true the work is deferred until the next vblank (as if count has been specified as crtc vblank count + 1).

If work is already scheduled, this function will reschedule said work using the new count. This can be used for self-rearming work items.

Return

1 if work was successfully (re)scheduled, 0 if it was either already scheduled or cancelled, or a negative error code on failure.

bool drm_vblank_work_cancel_sync(struct drm_vblank_work *work)¶: cancel a vblank work and wait for it to finish executing

Parameters

struct drm_vblank_work *work: vblank work to cancel

Description

Cancel an already scheduled vblank work and wait for its execution to finish.

On return, work is guaranteed to no longer be scheduled or running, even if it’s self-arming.

Return

True if the work was cancelled before it started to execute, false otherwise.

void drm_vblank_work_flush(struct drm_vblank_work *work)¶: wait for a scheduled vblank work to finish executing

Parameters

struct drm_vblank_work *work: vblank work to flush

Description

Wait until work has finished executing once.

void drm_vblank_work_init(struct drm_vblank_work *work, struct drm_crtc *crtc, void (*func)(struct kthread_work *work))¶: initialize a vblank work item

Parameters

struct drm_vblank_work *work: vblank work item
struct drm_crtc *crtc: CRTC whose vblank will trigger the work execution
void (*func)(struct kthread_work *work): work function to be executed

Description

Initialize a vblank work item for a specific crtc.