AMDgpu Display Manager ¶

The AMDgpu display manager, amdgpu_dm (or even simpler, dm) sits between DRM and DC. It acts as a liaison, converting DRM requests into DC requests, and DC responses into DRM responses.

The root control structure is struct amdgpu_display_manager.

struct dm_compressor_info¶: Buffer info used by frame buffer compression

Definition:

struct dm_compressor_info {
    void *cpu_addr;
    struct amdgpu_bo *bo_ptr;
    uint64_t gpu_addr;
};

Members

cpu_addr: MMIO cpu addr
bo_ptr: Pointer to the buffer object
gpu_addr: MMIO gpu addr

struct dmub_hpd_work¶: Handle time consuming work in low priority outbox IRQ

Definition:

struct dmub_hpd_work {
    struct work_struct handle_hpd_work;
    struct dmub_notification *dmub_notify;
    struct amdgpu_device *adev;
};

Members

handle_hpd_work: Work to be executed in a separate thread to handle hpd_low_irq
dmub_notify: notification for callback function
adev: amdgpu_device pointer

struct vblank_control_work¶: Work data for vblank control

Definition:

struct vblank_control_work {
    struct work_struct work;
    struct amdgpu_display_manager *dm;
    struct amdgpu_crtc *acrtc;
    struct dc_stream_state *stream;
    bool enable;
};

Members

work: Kernel work data for the work event
dm: amdgpu display manager device
acrtc: amdgpu CRTC instance for which the event has occurred
stream: DC stream for which the event has occurred
enable: true if enabling vblank

struct idle_workqueue¶: Work data for periodic action in idle

Definition:

struct idle_workqueue {
    struct work_struct work;
    struct amdgpu_display_manager *dm;
    bool enable;
    bool running;
};

Members

work: Kernel work data for the work event
dm: amdgpu display manager device
enable: true if idle worker is enabled
running: true if idle worker is running

struct amdgpu_dm_backlight_caps¶: Information about backlight

Definition:

struct amdgpu_dm_backlight_caps {
    union dpcd_sink_ext_caps *ext_caps;
    u32 aux_min_input_signal;
    u32 aux_max_input_signal;
    int min_input_signal;
    int max_input_signal;
    bool caps_valid;
    bool aux_support;
    u8 ac_level;
    u8 dc_level;
};

Members

ext_caps: Keep the data struct with all the information about the display support for HDR.
aux_min_input_signal: Min brightness value supported by the display
aux_max_input_signal: Max brightness value supported by the display in nits.
min_input_signal: minimum possible input in range 0-255.
max_input_signal: maximum possible input in range 0-255.
caps_valid: true if these values are from the ACPI interface.
aux_support: Describes if the display supports AUX backlight.
ac_level: the default brightness if booted on AC
dc_level: the default brightness if booted on DC

Description

Describe the backlight support for ACPI or eDP AUX.

struct dal_allocation¶: Tracks mapped FB memory for SMU communication

Definition:

struct dal_allocation {
    struct list_head list;
    struct amdgpu_bo *bo;
    void *cpu_ptr;
    u64 gpu_addr;
};

Members

list: list of dal allocations
bo: GPU buffer object
cpu_ptr: CPU virtual address of the GPU buffer object
gpu_addr: GPU virtual address of the GPU buffer object

struct hpd_rx_irq_offload_work_queue¶: Work queue to handle hpd_rx_irq offload work

Definition:

struct hpd_rx_irq_offload_work_queue {
    struct workqueue_struct *wq;
    spinlock_t offload_lock;
    bool is_handling_link_loss;
    bool is_handling_mst_msg_rdy_event;
    struct amdgpu_dm_connector *aconnector;
};

Members

wq: workqueue structure to queue offload work.
offload_lock: To protect fields of offload work queue.
is_handling_link_loss: Used to prevent inserting link loss event when we’re handling link loss
is_handling_mst_msg_rdy_event: Used to prevent inserting mst message ready event when we’re already handling mst message ready event
aconnector: The aconnector that this work queue is attached to

struct hpd_rx_irq_offload_work¶: hpd_rx_irq offload work structure

Definition:

struct hpd_rx_irq_offload_work {
    struct work_struct work;
    union hpd_irq_data data;
    struct hpd_rx_irq_offload_work_queue *offload_wq;
};

Members

work: offload work
data: reference irq data which is used while handling offload work
offload_wq: offload work queue that this work is queued to

struct amdgpu_display_manager¶: Central amdgpu display manager device

Definition:

struct amdgpu_display_manager {
    struct dc *dc;
    struct dmub_srv *dmub_srv;
    struct dmub_notification *dmub_notify;
    dmub_notify_interrupt_callback_t dmub_callback[AMDGPU_DMUB_NOTIFICATION_MAX];
    bool dmub_thread_offload[AMDGPU_DMUB_NOTIFICATION_MAX];
    struct dmub_srv_fb_info *dmub_fb_info;
    const struct firmware *dmub_fw;
    struct amdgpu_bo *dmub_bo;
    u64 dmub_bo_gpu_addr;
    void *dmub_bo_cpu_addr;
    uint32_t dmcub_fw_version;
    struct cgs_device *cgs_device;
    struct amdgpu_device *adev;
    struct drm_device *ddev;
    u16 display_indexes_num;
    struct drm_private_obj atomic_obj;
    struct mutex dc_lock;
    struct mutex audio_lock;
    struct drm_audio_component *audio_component;
    bool audio_registered;
    struct list_head irq_handler_list_low_tab[DAL_IRQ_SOURCES_NUMBER];
    struct list_head irq_handler_list_high_tab[DAL_IRQ_SOURCES_NUMBER];
    struct common_irq_params pflip_params[DC_IRQ_SOURCE_PFLIP_LAST - DC_IRQ_SOURCE_PFLIP_FIRST + 1];
    struct common_irq_params vblank_params[DC_IRQ_SOURCE_VBLANK6 - DC_IRQ_SOURCE_VBLANK1 + 1];
    struct common_irq_params vline0_params[DC_IRQ_SOURCE_DC6_VLINE0 - DC_IRQ_SOURCE_DC1_VLINE0 + 1];
    struct common_irq_params vupdate_params[DC_IRQ_SOURCE_VUPDATE6 - DC_IRQ_SOURCE_VUPDATE1 + 1];
    struct common_irq_params dmub_trace_params[1];
    struct common_irq_params dmub_outbox_params[1];
    spinlock_t irq_handler_list_table_lock;
    struct backlight_device *backlight_dev[AMDGPU_DM_MAX_NUM_EDP];
    const struct dc_link *backlight_link[AMDGPU_DM_MAX_NUM_EDP];
    uint8_t num_of_edps;
    struct amdgpu_dm_backlight_caps backlight_caps[AMDGPU_DM_MAX_NUM_EDP];
    struct mod_freesync *freesync_module;
    struct hdcp_workqueue *hdcp_workqueue;
    struct workqueue_struct *vblank_control_workqueue;
    struct idle_workqueue *idle_workqueue;
    struct drm_atomic_state *cached_state;
    struct dc_state *cached_dc_state;
    struct dm_compressor_info compressor;
    const struct firmware *fw_dmcu;
    uint32_t dmcu_fw_version;
    const struct gpu_info_soc_bounding_box_v1_0 *soc_bounding_box;
    uint32_t active_vblank_irq_count;
#if defined(CONFIG_DRM_AMD_SECURE_DISPLAY);
    struct secure_display_context *secure_display_ctxs;
#endif;
    struct hpd_rx_irq_offload_work_queue *hpd_rx_offload_wq;
    struct amdgpu_encoder mst_encoders[AMDGPU_DM_MAX_CRTC];
    bool force_timing_sync;
    bool disable_hpd_irq;
    bool dmcub_trace_event_en;
    struct list_head da_list;
    struct completion dmub_aux_transfer_done;
    struct workqueue_struct *delayed_hpd_wq;
    u32 brightness[AMDGPU_DM_MAX_NUM_EDP];
    u32 actual_brightness[AMDGPU_DM_MAX_NUM_EDP];
    bool aux_hpd_discon_quirk;
    struct mutex dpia_aux_lock;
    struct dml2_soc_bb *bb_from_dmub;
};

Members

dc

Display Core control structure

dmub_srv

DMUB service, used for controlling the DMUB on hardware that supports it. The pointer to the dmub_srv will be NULL on hardware that does not support it.

dmub_notify

Notification from DMUB.

dmub_callback

Callback functions to handle notification from DMUB.

dmub_thread_offload

Flag to indicate if callback is offload.

dmub_fb_info

Framebuffer regions for the DMUB.

dmub_fw

DMUB firmware, required on hardware that has DMUB support.

dmub_bo

Buffer object for the DMUB.

dmub_bo_gpu_addr

GPU virtual address for the DMUB buffer object.

dmub_bo_cpu_addr

CPU address for the DMUB buffer object.

dmcub_fw_version

DMCUB firmware version.

cgs_device

The Common Graphics Services device. It provides an interface for accessing registers.

adev

AMDGPU base driver structure

ddev

DRM base driver structure

display_indexes_num

Max number of display streams supported

atomic_obj

In combination with dm_atomic_state it helps manage global atomic state that doesn’t map cleanly into existing drm resources, like dc_context.

dc_lock

Guards access to DC functions that can issue register write sequences.

audio_lock

Guards access to audio instance changes.

audio_component

Used to notify ELD changes to sound driver.

audio_registered

True if the audio component has been registered successfully, false otherwise.

irq_handler_list_low_tab

Low priority IRQ handler table.

It is a n*m table consisting of n IRQ sources, and m handlers per IRQ source. Low priority IRQ handlers are deferred to a workqueue to be processed. Hence, they can sleep.

Note that handlers are called in the same order as they were registered (FIFO).

irq_handler_list_high_tab

High priority IRQ handler table.

It is a n*m table, same as irq_handler_list_low_tab. However, handlers in this table are not deferred and are called immediately.

pflip_params

Page flip IRQ parameters, passed to registered handlers when triggered.

vblank_params

Vertical blanking IRQ parameters, passed to registered handlers when triggered.

vline0_params

OTG vertical interrupt0 IRQ parameters, passed to registered handlers when triggered.

vupdate_params

Vertical update IRQ parameters, passed to registered handlers when triggered.

dmub_trace_params

DMUB trace event IRQ parameters, passed to registered handlers when triggered.

dmub_outbox_params

DMUB Outbox parameters

irq_handler_list_table_lock

Synchronizes access to IRQ tables

backlight_dev

Backlight control device

backlight_link

Link on which to control backlight

num_of_edps

number of backlight eDPs

backlight_caps

Capabilities of the backlight device

freesync_module

Module handling freesync calculations

hdcp_workqueue

AMDGPU content protection queue

vblank_control_workqueue

Deferred work for vblank control events.

idle_workqueue

Periodic work for idle events.

cached_state

Caches device atomic state for suspend/resume

cached_dc_state

Cached state of content streams

compressor

Frame buffer compression buffer. See struct dm_compressor_info

fw_dmcu

Reference to DMCU firmware

dmcu_fw_version

Version of the DMCU firmware

soc_bounding_box

gpu_info FW provided soc bounding box struct or 0 if not available in FW

active_vblank_irq_count

number of currently active vblank irqs

secure_display_ctxs

Store the ROI information and the work_struct to command dmub and psp for all crtcs.

hpd_rx_offload_wq

Work queue to offload works of hpd_rx_irq

mst_encoders

fake encoders used for DP MST.

force_timing_sync

set via debugfs. When set, indicates that all connected displays will be forced to synchronize.

disable_hpd_irq

disables all HPD and HPD RX interrupt handling in the driver when true

dmcub_trace_event_en

enable dmcub trace events

da_list

DAL fb memory allocation list, for communication with SMU.

dmub_aux_transfer_done

struct completion used to indicate when DMUB transfers are done

delayed_hpd_wq

work queue used to delay DMUB HPD work

brightness

cached backlight values.

actual_brightness

last successfully applied backlight values.

aux_hpd_discon_quirk

quirk for hpd discon while aux is on-going. occurred on certain intel platform

dpia_aux_lock

Guards access to DPIA AUX

bb_from_dmub

Bounding box data read from dmub during early initialization for DCN4+

struct amdgpu_hdmi_vsdb_info¶: Keep track of the VSDB info

Definition:

struct amdgpu_hdmi_vsdb_info {
    unsigned int amd_vsdb_version;
    bool freesync_supported;
    unsigned int min_refresh_rate_hz;
    unsigned int max_refresh_rate_hz;
    bool replay_mode;
};

Members

amd_vsdb_version: Vendor Specific Data Block Version, should be used to determine which Vendor Specific InfoFrame (VSIF) to send.
freesync_supported: FreeSync Supported.
min_refresh_rate_hz: FreeSync Minimum Refresh Rate in Hz.
max_refresh_rate_hz: FreeSync Maximum Refresh Rate in Hz
replay_mode: Replay supported

Description

AMDGPU supports FreeSync over HDMI by using the VSDB section, and this struct is useful to keep track of the display-specific information about FreeSync.

Lifecycle ¶

DM (and consequently DC) is registered in the amdgpu base driver as a IP block. When CONFIG_DRM_AMD_DC is enabled, the DM device IP block is added to the base driver’s device list to be initialized and torn down accordingly.

The functions to do so are provided as hooks in struct amd_ip_funcs.

int dm_hw_init(struct amdgpu_ip_block *ip_block)¶: Initialize DC device

Parameters

struct amdgpu_ip_block *ip_block: Pointer to the amdgpu_ip_block for this hw instance.

Description

Initialize the struct amdgpu_display_manager device. This involves calling the initializers of each DM component, then populating the struct with them.

Although the function implies hardware initialization, both hardware and software are initialized here. Splitting them out to their relevant init hooks is a future TODO item.

Some notable things that are initialized here:

Display Core, both software and hardware
DC modules that we need (freesync and color management)
DRM software states
Interrupt sources and handlers
Vblank support
Debug FS entries, if enabled

int dm_hw_fini(struct amdgpu_ip_block *ip_block)¶: Teardown DC device

Parameters

struct amdgpu_ip_block *ip_block: Pointer to the amdgpu_ip_block for this hw instance.

Description

Teardown components within struct amdgpu_display_manager that require cleanup. This involves cleaning up the DRM device, DC, and any modules that were loaded. Also flush IRQ workqueues and disable them.

Interrupts ¶

DM provides another layer of IRQ management on top of what the base driver already provides. This is something that could be cleaned up, and is a future TODO item.

The base driver provides IRQ source registration with DRM, handler registration into the base driver’s IRQ table, and a handler callback amdgpu_irq_handler(), with which DRM calls on interrupts. This generic handler looks up the IRQ table, and calls the respective amdgpu_irq_src_funcs.process hookups.

What DM provides on top are two IRQ tables specifically for top-half and bottom-half IRQ handling, with the bottom-half implementing workqueues:

amdgpu_display_manager.irq_handler_list_high_tab
amdgpu_display_manager.irq_handler_list_low_tab

They override the base driver’s IRQ table, and the effect can be seen in the hooks that DM provides for amdgpu_irq_src_funcs.process. They are all set to the DM generic handler amdgpu_dm_irq_handler(), which looks up DM’s IRQ tables. However, in order for base driver to recognize this hook, DM still needs to register the IRQ with the base driver. See dce110_register_irq_handlers() and dcn10_register_irq_handlers().

To expose DC’s hardware interrupt toggle to the base driver, DM implements amdgpu_irq_src_funcs.set hooks. Base driver calls it through amdgpu_irq_update() to enable or disable the interrupt.

struct amdgpu_dm_irq_handler_data¶: Data for DM interrupt handlers.

Definition:

struct amdgpu_dm_irq_handler_data {
    struct list_head list;
    interrupt_handler handler;
    void *handler_arg;
    struct amdgpu_display_manager *dm;
    enum dc_irq_source irq_source;
    struct work_struct work;
};

Members

list: Linked list entry referencing the next/previous handler
handler: Handler function
handler_arg: Argument passed to the handler when triggered
dm: DM which this handler belongs to
irq_source: DC interrupt source that this handler is registered for
work: work struct

void dm_irq_work_func(struct work_struct *work)¶: Handle an IRQ outside of the interrupt handler proper.

Parameters

struct work_struct *work: work struct

void unregister_all_irq_handlers(struct amdgpu_device *adev)¶: Cleans up handlers from the DM IRQ table

Parameters

struct amdgpu_device *adev: The base driver device containing the DM device

Description

Go through low and high context IRQ tables and deallocate handlers.

void *amdgpu_dm_irq_register_interrupt(struct amdgpu_device *adev, struct dc_interrupt_params *int_params, void (*ih)(void*), void *handler_args)¶: Register a handler within DM.

Parameters

struct amdgpu_device *adev: The base driver device containing the DM device.
struct dc_interrupt_params *int_params: Interrupt parameters containing the source, and handler context
void (*ih)(void *): Function pointer to the interrupt handler to register
void *handler_args: Arguments passed to the handler when the interrupt occurs

Description

Register an interrupt handler for the given IRQ source, under the given context. The context can either be high or low. High context handlers are executed directly within ISR context, while low context is executed within a workqueue, thereby allowing operations that sleep.

Registered handlers are called in a FIFO manner, i.e. the most recently registered handler will be called first.

Return

Handler data struct amdgpu_dm_irq_handler_data containing the IRQ: source, handler function, and args

void amdgpu_dm_irq_unregister_interrupt(struct amdgpu_device *adev, enum dc_irq_source irq_source, void *ih)¶: Remove a handler from the DM IRQ table

Parameters

struct amdgpu_device *adev: The base driver device containing the DM device
enum dc_irq_source irq_source: IRQ source to remove the given handler from
void *ih: Function pointer to the interrupt handler to unregister

Description

Go through both low and high context IRQ tables, and find the given handler for the given irq source. If found, remove it. Otherwise, do nothing.

int amdgpu_dm_irq_init(struct amdgpu_device *adev)¶: Initialize DM IRQ management

Parameters

struct amdgpu_device *adev: The base driver device containing the DM device

Description

Initialize DM’s high and low context IRQ tables.

The N by M table contains N IRQ sources, with M struct amdgpu_dm_irq_handler_data hooked together in a linked list. The list_heads are initialized here. When an interrupt n is triggered, all m handlers are called in sequence, FIFO according to registration order.

The low context table requires special steps to initialize, since handlers will be deferred to a workqueue. See struct irq_list_head.

void amdgpu_dm_irq_fini(struct amdgpu_device *adev)¶: Tear down DM IRQ management

Parameters

struct amdgpu_device *adev: The base driver device containing the DM device

Description

Flush all work within the low context IRQ table.

int amdgpu_dm_irq_handler(struct amdgpu_device *adev, struct amdgpu_irq_src *source, struct amdgpu_iv_entry *entry)¶: Generic DM IRQ handler

Parameters

struct amdgpu_device *adev: amdgpu base driver device containing the DM device
struct amdgpu_irq_src *source: Unused
struct amdgpu_iv_entry *entry: Data about the triggered interrupt

Description

Calls all registered high irq work immediately, and schedules work for low irq. The DM IRQ table is used to find the corresponding handlers.

void amdgpu_dm_hpd_init(struct amdgpu_device *adev)¶: hpd setup callback.

Parameters

struct amdgpu_device *adev: amdgpu_device pointer

Description

Setup the hpd pins used by the card (evergreen+). Enable the pin, set the polarity, and enable the hpd interrupts.

void amdgpu_dm_hpd_fini(struct amdgpu_device *adev)¶: hpd tear down callback.

Parameters

struct amdgpu_device *adev: amdgpu_device pointer

Description

Tear down the hpd pins used by the card (evergreen+). Disable the hpd interrupts.

void dm_pflip_high_irq(void *interrupt_params)¶: Handle pageflip interrupt

Parameters

void *interrupt_params: ignored

Description

Handles the pageflip interrupt by notifying all interested parties that the pageflip has been completed.

void dm_crtc_high_irq(void *interrupt_params)¶: Handles CRTC interrupt

Parameters

void *interrupt_params: used for determining the CRTC instance

Description

Handles the CRTC/VSYNC interrupt by notfying DRM’s VBLANK event handler.

Atomic Implementation ¶

WIP

void amdgpu_dm_atomic_commit_tail(struct drm_atomic_state *state)¶: AMDgpu DM’s commit tail implementation.

Parameters

struct drm_atomic_state *state: The atomic state to commit

Description

This will tell DC to commit the constructed DC state from atomic_check, programming the hardware. Any failures here implies a hardware failure, since atomic check should have filtered anything non-kosher.

int amdgpu_dm_atomic_check(struct drm_device *dev, struct drm_atomic_state *state)¶: Atomic check implementation for AMDgpu DM.

Parameters

struct drm_device *dev: The DRM device
struct drm_atomic_state *state: The atomic state to commit

Description

Validate that the given atomic state is programmable by DC into hardware. This involves constructing a struct dc_state reflecting the new hardware state we wish to commit, then querying DC to see if it is programmable. It’s important not to modify the existing DC state. Otherwise, atomic_check may unexpectedly commit hardware changes.

When validating the DC state, it’s important that the right locks are acquired. For full updates case which removes/adds/updates streams on one CRTC while flipping on another CRTC, acquiring global lock will guarantee that any such full update commit will wait for completion of any outstanding flip using DRMs synchronization events.

Note that DM adds the affected connectors for all CRTCs in state, when that might not seem necessary. This is because DC stream creation requires the DC sink, which is tied to the DRM connector state. Cleaning this up should be possible but non-trivial - a possible TODO item.

Return

-Error code if validation failed.

Color Management Properties ¶

The DC interface to HW gives us the following color management blocks per pipe (surface):

Input gamma LUT (de-normalized)
Input CSC (normalized)
Surface degamma LUT (normalized)
Surface CSC (normalized)
Surface regamma LUT (normalized)
Output CSC (normalized)

But these aren’t a direct mapping to DRM color properties. The current DRM interface exposes CRTC degamma, CRTC CTM and CRTC regamma while our hardware is essentially giving:

Plane CTM -> Plane degamma -> Plane CTM -> Plane regamma -> Plane CTM

The input gamma LUT block isn’t really applicable here since it operates on the actual input data itself rather than the HW fp representation. The input and output CSC blocks are technically available to use as part of the DC interface but are typically used internally by DC for conversions between color spaces. These could be blended together with user adjustments in the future but for now these should remain untouched.

The pipe blending also happens after these blocks so we don’t actually support any CRTC props with correct blending with multiple planes - but we can still support CRTC color management properties in DM in most single plane cases correctly with clever management of the DC interface in DM.

As per DRM documentation, blocks should be in hardware bypass when their respective property is set to NULL. A linear DGM/RGM LUT should also considered as putting the respective block into bypass mode.

This means that the following configuration is assumed to be the default:

Plane DGM Bypass -> Plane CTM Bypass -> Plane RGM Bypass -> ... CRTC DGM Bypass -> CRTC CTM Bypass -> CRTC RGM Bypass

void amdgpu_dm_init_color_mod(void)¶: Initialize the color module.

Parameters

void: no arguments

Description

We’re not using the full color module, only certain components. Only call setup functions for components that we need.

const struct drm_color_lut *__extract_blob_lut(const struct drm_property_blob *blob, uint32_t *size)¶: Extracts the DRM lut and lut size from a blob.

Parameters

const struct drm_property_blob *blob: DRM color mgmt property blob
uint32_t *size: lut size

Return

DRM LUT or NULL

bool __is_lut_linear(const struct drm_color_lut *lut, uint32_t size)¶: check if the given lut is a linear mapping of values

Parameters

const struct drm_color_lut *lut: given lut to check values
uint32_t size: lut size

Description

It is considered linear if the lut represents: f(a) = (0xFF00/MAX_COLOR_LUT_ENTRIES-1)a; for integer a in [0, MAX_COLOR_LUT_ENTRIES)

Return

True if the given lut is a linear mapping of values, i.e. it acts like a bypass LUT. Otherwise, false.

void __drm_lut_to_dc_gamma(const struct drm_color_lut *lut, struct dc_gamma *gamma, bool is_legacy)¶: convert the drm_color_lut to dc_gamma.

Parameters

const struct drm_color_lut *lut: DRM lookup table for color conversion
struct dc_gamma *gamma: DC gamma to set entries
bool is_legacy: legacy or atomic gamma

Description

The conversion depends on the size of the lut - whether or not it’s legacy.

void __drm_ctm_to_dc_matrix(const struct drm_color_ctm *ctm, struct fixed31_32 *matrix)¶: converts a DRM CTM to a DC CSC float matrix

Parameters

const struct drm_color_ctm *ctm: DRM color transformation matrix
struct fixed31_32 *matrix: DC CSC float matrix

Description

The matrix needs to be a 3x4 (12 entry) matrix.

void __drm_ctm_3x4_to_dc_matrix(const struct drm_color_ctm_3x4 *ctm, struct fixed31_32 *matrix)¶: converts a DRM CTM 3x4 to a DC CSC float matrix

Parameters

const struct drm_color_ctm_3x4 *ctm: DRM color transformation matrix with 3x4 dimensions
struct fixed31_32 *matrix: DC CSC float matrix

Description

The matrix needs to be a 3x4 (12 entry) matrix.

int __set_legacy_tf(struct dc_transfer_func *func, const struct drm_color_lut *lut, uint32_t lut_size, bool has_rom)¶: Calculates the legacy transfer function

Parameters

struct dc_transfer_func *func: transfer function
const struct drm_color_lut *lut: lookup table that defines the color space
uint32_t lut_size: size of respective lut
bool has_rom: if ROM can be used for hardcoded curve

Description

Only for sRGB input space

Return

0 in case of success, -ENOMEM if fails

int __set_output_tf(struct dc_transfer_func *func, const struct drm_color_lut *lut, uint32_t lut_size, bool has_rom)¶: calculates the output transfer function based on expected input space.

Parameters

struct dc_transfer_func *func: transfer function
const struct drm_color_lut *lut: lookup table that defines the color space
uint32_t lut_size: size of respective lut
bool has_rom: if ROM can be used for hardcoded curve

Return

0 in case of success. -ENOMEM if fails.

int __set_input_tf(struct dc_color_caps *caps, struct dc_transfer_func *func, const struct drm_color_lut *lut, uint32_t lut_size)¶: calculates the input transfer function based on expected input space.

Parameters

struct dc_color_caps *caps: dc color capabilities
struct dc_transfer_func *func: transfer function
const struct drm_color_lut *lut: lookup table that defines the color space
uint32_t lut_size: size of respective lut.

Return

0 in case of success. -ENOMEM if fails.

int amdgpu_dm_verify_lut3d_size(struct amdgpu_device *adev, struct drm_plane_state *plane_state)¶: verifies if 3D LUT is supported and if user shaper and 3D LUTs match the hw supported size

Parameters

struct amdgpu_device *adev: amdgpu device
struct drm_plane_state *plane_state: the DRM plane state

Description

Verifies if pre-blending (DPP) 3D LUT is supported by the HW (DCN 2.0 or newer) and if the user shaper and 3D LUTs match the supported size.

Return

0 on success. -EINVAL if lut size are invalid.

int amdgpu_dm_verify_lut_sizes(const struct drm_crtc_state *crtc_state)¶: verifies if DRM luts match the hw supported sizes

Parameters

const struct drm_crtc_state *crtc_state: the DRM CRTC state

Description

Verifies that the Degamma and Gamma LUTs attached to the crtc_state are of the expected size.

Return

0 on success. -EINVAL if any lut sizes are invalid.

int amdgpu_dm_update_crtc_color_mgmt(struct dm_crtc_state *crtc)¶: Maps DRM color management to DC stream.

Parameters

struct dm_crtc_state *crtc: amdgpu_dm crtc state

Description

With no plane level color management properties we’re free to use any of the HW blocks as long as the CRTC CTM always comes before the CRTC RGM and after the CRTC DGM.

The CRTC RGM block will be placed in the RGM LUT block if it is non-linear.
The CRTC DGM block will be placed in the DGM LUT block if it is non-linear.
The CRTC CTM will be placed in the gamut remap block if it is non-linear.

The RGM block is typically more fully featured and accurate across all ASICs - DCE can’t support a custom non-linear CRTC DGM.

For supporting both plane level color management and CRTC level color management at once we have to either restrict the usage of CRTC properties or blend adjustments together.

Return

0 on success. Error code if setup fails.

int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc, struct drm_plane_state *plane_state, struct dc_plane_state *dc_plane_state)¶: Maps DRM color management to DC plane.

Parameters

struct dm_crtc_state *crtc: amdgpu_dm crtc state
struct drm_plane_state *plane_state: DRM plane state
struct dc_plane_state *dc_plane_state: target DC surface

Description

Update the underlying dc_stream_state’s input transfer function (ITF) in preparation for hardware commit. The transfer function used depends on the preparation done on the stream for color management.

Return

0 on success. -ENOMEM if mem allocation fails.

DC Color Capabilities between DCN generations ¶

DRM/KMS framework defines three CRTC color correction properties: degamma, color transformation matrix (CTM) and gamma, and two properties for degamma and gamma LUT sizes. AMD DC programs some of the color correction features pre-blending but DRM/KMS has not per-plane color correction properties.

In general, the DRM CRTC color properties are programmed to DC, as follows: CRTC gamma after blending, and CRTC degamma pre-blending. Although CTM is programmed after blending, it is mapped to DPP hw blocks (pre-blending). Other color caps available in the hw is not currently exposed by DRM interface and are bypassed.

Color management caps (DPP and MPC)

Modules/color calculates various color operations which are translated to abstracted HW. DCE 5-12 had almost no important changes, but starting with DCN1, every new generation comes with fairly major differences in color pipeline. Therefore, we abstract color pipe capabilities so modules/DM can decide mapping to HW block based on logical capabilities.

struct rom_curve_caps¶: predefined transfer function caps for degamma and regamma

Definition:

struct rom_curve_caps {
    uint16_t srgb : 1;
    uint16_t bt2020 : 1;
    uint16_t gamma2_2 : 1;
    uint16_t pq : 1;
    uint16_t hlg : 1;
};

Members

srgb: RGB color space transfer func
bt2020: BT.2020 transfer func
gamma2_2: standard gamma
pq: perceptual quantizer transfer function
hlg: hybrid log–gamma transfer function

struct dpp_color_caps¶: color pipeline capabilities for display pipe and plane blocks

Definition:

struct dpp_color_caps {
    uint16_t dcn_arch : 1;
    uint16_t input_lut_shared : 1;
    uint16_t icsc : 1;
    uint16_t dgam_ram : 1;
    uint16_t post_csc : 1;
    uint16_t gamma_corr : 1;
    uint16_t hw_3d_lut : 1;
    uint16_t ogam_ram : 1;
    uint16_t ocsc : 1;
    uint16_t dgam_rom_for_yuv : 1;
    struct rom_curve_caps dgam_rom_caps;
    struct rom_curve_caps ogam_rom_caps;
};

Members

dcn_arch: all DCE generations treated the same
input_lut_shared: shared with DGAM. Input LUT is different than most LUTs, just plain 256-entry lookup
icsc: input color space conversion
dgam_ram: programmable degamma LUT
post_csc: post color space conversion, before gamut remap
gamma_corr: degamma correction
hw_3d_lut: 3D LUT support. It implies a shaper LUT before. It may be shared with MPC by setting mpc:shared_3d_lut flag
ogam_ram: programmable out/blend gamma LUT
ocsc: output color space conversion
dgam_rom_for_yuv: pre-defined degamma LUT for YUV planes
dgam_rom_caps: pre-definied curve caps for degamma 1D LUT
ogam_rom_caps: pre-definied curve caps for regamma 1D LUT

Note

hdr_mult and gamut remap (CTM) are always available in DPP (in that order)

struct mpc_color_caps¶: color pipeline capabilities for multiple pipe and plane combined blocks

Definition:

struct mpc_color_caps {
    uint16_t gamut_remap : 1;
    uint16_t ogam_ram : 1;
    uint16_t ocsc : 1;
    uint16_t num_3dluts : 3;
    uint16_t shared_3d_lut:1;
    struct rom_curve_caps ogam_rom_caps;
};

Members

gamut_remap: color transformation matrix
ogam_ram: programmable out gamma LUT
ocsc: output color space conversion matrix
num_3dluts: MPC 3D LUT; always assumes a preceding shaper LUT
shared_3d_lut: shared 3D LUT flag. Can be either DPP or MPC, but single instance
ogam_rom_caps: pre-definied curve caps for regamma 1D LUT

struct dc_color_caps¶: color pipes capabilities for DPP and MPC hw blocks

Definition:

struct dc_color_caps {
    struct dpp_color_caps dpp;
    struct mpc_color_caps mpc;
};

Members

dpp: color pipes caps for DPP
mpc: color pipes caps for MPC

enum pipe_split_policy¶: Pipe split strategy supported by DCN

Constants

MPC_SPLIT_DYNAMIC: DC will automatically decide how to split the pipe in order to bring the best trade-off between performance and power consumption. This is the recommended option.
MPC_SPLIT_AVOID: Avoid pipe split, which means that DC will not try any sort of split optimization.
MPC_SPLIT_AVOID_MULT_DISP: With this option, DC will only try to optimize the pipe utilization when using a single display; if the user connects to a second display, DC will avoid pipe split.

Description

This enum is used to define the pipe split policy supported by DCN. By default, DC favors MPC_SPLIT_DYNAMIC.

struct dc_validation_set¶: Struct to store surface/stream associations for validation

Definition:

struct dc_validation_set {
    struct dc_stream_state *stream;
    struct dc_plane_state *plane_states[MAX_SURFACES];
    uint8_t plane_count;
};

Members

stream: Stream state properties
plane_states: Surface state
plane_count: Total of active planes

The color pipeline has undergone major changes between DCN hardware generations. What’s possible to do before and after blending depends on hardware capabilities, as illustrated below by the DCN 2.0 and DCN 3.0 families schemas.

DCN 2.0 family color caps and mapping

../../../_images/dcn2_cm_drm_current.svg

DCN 3.0 family color caps and mapping

../../../_images/dcn3_cm_drm_current.svg

Blend Mode Properties ¶

Pixel blend mode is a DRM plane composition property of drm_plane used to describes how pixels from a foreground plane (fg) are composited with the background plane (bg). Here, we present main concepts of DRM blend mode to help to understand how this property is mapped to AMD DC interface. See more about this DRM property and the alpha blending equations in DRM Plane Composition Properties.

Basically, a blend mode sets the alpha blending equation for plane composition that fits the mode in which the alpha channel affects the state of pixel color values and, therefore, the resulted pixel color. For example, consider the following elements of the alpha blending equation:

fg.rgb: Each of the RGB component values from the foreground’s pixel.
fg.alpha: Alpha component value from the foreground’s pixel.
bg.rgb: Each of the RGB component values from the background.
plane_alpha: Plane alpha value set by the plane “alpha” property, see more in DRM Plane Composition Properties.

in the basic alpha blending equation:

out.rgb = alpha * fg.rgb + (1 - alpha) * bg.rgb

the alpha channel value of each pixel in a plane is ignored and only the plane alpha affects the resulted pixel color values.

DRM has three blend mode to define the blend formula in the plane composition:

None: Blend formula that ignores the pixel alpha.
Pre-multiplied: Blend formula that assumes the pixel color values in a plane was already pre-multiplied by its own alpha channel before storage.
Coverage: Blend formula that assumes the pixel color values were not pre-multiplied with the alpha channel values.

and pre-multiplied is the default pixel blend mode, that means, when no blend mode property is created or defined, DRM considers the plane’s pixels has pre-multiplied color values. On IGT GPU tools, the kms_plane_alpha_blend test provides a set of subtests to verify plane alpha and blend mode properties.

The DRM blend mode and its elements are then mapped by AMDGPU display manager (DM) to program the blending configuration of the Multiple Pipe/Plane Combined (MPC), as follows:

struct mpcc_blnd_cfg¶: MPCC blending configuration

Definition:

struct mpcc_blnd_cfg {
    struct tg_color black_color;
    enum mpcc_alpha_blend_mode alpha_mode;
    bool pre_multiplied_alpha;
    int global_gain;
    int global_alpha;
    bool overlap_only;
    int bottom_gain_mode;
    int background_color_bpc;
    int top_gain;
    int bottom_inside_gain;
    int bottom_outside_gain;
};

Members

black_color: background color.
alpha_mode: alpha blend mode (MPCC_ALPHA_BLND_MODE).
pre_multiplied_alpha: Whether pixel color values were pre-multiplied by the alpha channel (MPCC_ALPHA_MULTIPLIED_MODE).
global_gain: Used when blend mode considers both pixel alpha and plane.
global_alpha: Plane alpha value.
overlap_only: Whether overlapping of different planes is allowed.
bottom_gain_mode: Blend mode for bottom gain setting.
background_color_bpc: Background color for bpc.
top_gain: Top gain setting.
bottom_inside_gain: Blend mode for bottom inside.
bottom_outside_gain: Blend mode for bottom outside.

Therefore, the blending configuration for a single MPCC instance on the MPC tree is defined by mpcc_blnd_cfg, where pre_multiplied_alpha is the alpha pre-multiplied mode flag used to set MPCC_ALPHA_MULTIPLIED_MODE. It controls whether alpha is multiplied (true/false), being only true for DRM pre-multiplied blend mode. mpcc_alpha_blend_mode defines the alpha blend mode regarding pixel alpha and plane alpha values. It sets one of the three modes for MPCC_ALPHA_BLND_MODE, as described below.

enum mpcc_alpha_blend_mode¶: define the alpha blend mode regarding pixel alpha and plane alpha values

Constants

MPCC_ALPHA_BLEND_MODE_PER_PIXEL_ALPHA: per pixel alpha using DPP alpha value
MPCC_ALPHA_BLEND_MODE_PER_PIXEL_ALPHA_COMBINED_GLOBAL_GAIN: per pixel alpha using DPP alpha value multiplied by a global gain (plane alpha)
MPCC_ALPHA_BLEND_MODE_GLOBAL_ALPHA: global alpha value, ignores pixel alpha and consider only plane alpha

DM then maps the elements of enum mpcc_alpha_blend_mode to those in the DRM blend formula, as follows:

MPC pixel alpha matches DRM fg.alpha as the alpha component value from the plane’s pixel
MPC global alpha matches DRM plane_alpha when the pixel alpha should be ignored and, therefore, pixel values are not pre-multiplied
MPC global gain assumes MPC global alpha value when both DRM fg.alpha and DRM plane_alpha participate in the blend equation

In short, fg.alpha is ignored by selecting MPCC_ALPHA_BLEND_MODE_GLOBAL_ALPHA. On the other hand, (plane_alpha * fg.alpha) component becomes available by selecting MPCC_ALPHA_BLEND_MODE_PER_PIXEL_ALPHA_COMBINED_GLOBAL_GAIN. And the MPCC_ALPHA_MULTIPLIED_MODE defines if the pixel color values are pre-multiplied by alpha or not.

Blend configuration flow ¶

The alpha blending equation is configured from DRM to DC interface by the following path:

When updating a drm_plane_state, DM calls amdgpu_dm_plane_fill_blending_from_plane_state() that maps drm_plane_state attributes to dc_plane_info struct to be handled in the OS-agnostic component (DC).
On DC interface, struct mpcc_blnd_cfg programs the MPCC blend configuration considering the dc_plane_info input from DPP.