AMDgpu Display Manager¶
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Lifecycle¶
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Interrupts¶
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Atomic Implementation¶
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Color Management Properties¶
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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.
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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
DCN 3.0 family color caps and mapping
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:
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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.
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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 callsamdgpu_dm_plane_fill_blending_from_plane_state()
that mapsdrm_plane_state
attributes todc_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 thedc_plane_info
input from DPP.