On 07/17, Tales Lelo da Aparecida wrote: > On 16/07/2022 19:25, Melissa Wen wrote: > > AMD GPU display manager (DM) maps DRM pixel blend modes (None, > > Pre-multiplied, Coverage) to MPC hw blocks through blend configuration > > options. Describe relevant elements and how to set and test them to get > > the expected DRM blend mode on DCN hw. > > > > Signed-off-by: Melissa Wen <mwen@xxxxxxxxxx> > > --- > > .../gpu/amdgpu/display/display-manager.rst | 98 +++++++++++++++++++ > > Documentation/gpu/drm-kms.rst | 2 + > > 2 files changed, 100 insertions(+) > > > > diff --git a/Documentation/gpu/amdgpu/display/display-manager.rst b/Documentation/gpu/amdgpu/display/display-manager.rst > > index 8960a5f1fa66..7a495ed1f69e 100644 > > --- a/Documentation/gpu/amdgpu/display/display-manager.rst > > +++ b/Documentation/gpu/amdgpu/display/display-manager.rst > > @@ -84,3 +84,101 @@ families below. > > **DCN 3.0 family color caps and mapping** > > .. kernel-figure:: dcn3_cm_drm_current.svg > > + > > +Blend Mode Properties > > +===================== > > + > > +Pixel blend mode is a DRM plane composition property of :c:type:`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 :ref:`DRM Plane > > +Composition Properties <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 <plane_composition_properties>`. > > You forgot to use :ref: in here. > > > + > > +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: > > + > > +.. kernel-doc:: drivers/gpu/drm/amd/display/dc/inc/hw/mpc.h > > + :doc: mpc-overview > > + > > +.. kernel-doc:: drivers/gpu/drm/amd/display/dc/inc/hw/mpc.h > > + :functions: mpcc_blnd_cfg > > + > > +Therefore, the blending configuration for a single MPCC instance on the MPC > > +tree is defined by :c:type:`mpcc_blnd_cfg`, where > > +:c:type:`pre_multiplied_alpha` is the alpha pre-multiplied mode flag used to > > +set :c:type:`MPCC_ALPHA_MULTIPLIED_MODE`. It controls whether alpha is > > +multiplied (true/false), being only true for DRM pre-multiplied blend mode. > > +:c:type:`mpcc_alpha_blend_mode` defines the alpha blend mode regarding pixel > > +alpha and plane alpha values. It sets one of the three modes for > > +:c:type:`MPCC_ALPHA_BLND_MODE`, as described below. > > + > > +.. kernel-doc:: drivers/gpu/drm/amd/display/dc/inc/hw/mpc.h > > + :functions: mpcc_alpha_blend_mode > > + > > +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 > > +:c:type:`MPCC_ALPHA_BLEND_MODE_GLOBAL_ALPHA`. On the other hand, (plane_alpha * > > +fg.alpha) component becomes available by selecting > > +:c:type:`MPCC_ALPHA_BLEND_MODE_PER_PIXEL_ALPHA_COMBINED_GLOBAL_GAIN`. And the > > +:c:type:`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: > > + > > +1. When updating a :c:type:`drm_plane_state <drm_plane_state>`, DM calls > > + :c:type:`fill_blending_from_plane_state()` that maps > > + :c:type:`drm_plane_state <drm_plane_state>` attributes to > > + :c:type:`dc_plane_info <dc_plane_info>` struct to be handled in the > > + OS-agnostic component (DC). > > + > > +2. On DC interface, :c:type:`struct mpcc_blnd_cfg <mpcc_blnd_cfg>` programs the > > + MPCC blend configuration considering the :c:type:`dc_plane_info > > + <dc_plane_info>` input from DPP. > > diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst > > index d14bf1c35d7e..7ec9dbe18b65 100644 > > --- a/Documentation/gpu/drm-kms.rst > > +++ b/Documentation/gpu/drm-kms.rst > > @@ -532,6 +532,8 @@ Standard Plane Properties > > .. kernel-doc:: drivers/gpu/drm/drm_plane.c > > :doc: standard plane properties > > +.. _plane_composition_properties: > > + > > Plane Composition Properties > > ---------------------------- > > From a beginner's perspective, the changes from this series are readable, > but I cannot tell if there are any technical mistakes. So, > regarding readability and rendering htmldocs, apart from the nits I've > raised, this whole series is > > Reviewed-by: Tales Aparecida <tales.aparecida@xxxxxxxxx> > > Thanks for the patch series, Melissa, Hi Tales, Thanks for taking a look at this series and reviewing it carefully. Again, I'll address your comments in the next version. Best Regards, Melissa > Tales Aparecida
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