drm/amd/display: add Coverage blend mode for overlay plane

According to the KMS man page, there is a
"Coverage" alpha blend mode that assumes the
pixel color values have NOT been pre-multiplied
and will be done when the actual blending to
the background color values happens.

Previously, this mode hasn't been enabled
in our driver and it was assumed that all
normal overlay planes are pre-multiplied
by default.

When a 3rd party app is used to input a image
in a specific format, e.g. PNG, as a source
of a overlay plane to blend with the background
primary plane, the pixel color values are not
pre-multiplied. So by adding "Coverage" blend
mode, our driver will support those cases.

Issue fixed: Overlay plane alpha channel blending is incorrect
Issue tracker: https://gitlab.freedesktop.org/drm/amd/-/issues/1769

Reference:
https://dri.freedesktop.org/docs/drm/gpu/drm-kms.html#plane-composition-properties

Adding Coverage support also enables IGT
kms_plane_alpha_blend Coverage subtests:
1. coverage-7efc
2. coverage-vs-premult-vs-constant

Changes
1. Add DRM_MODE_BLEND_COVERAGE blend mode capability
2. Add "pre_multiplied_alpha" flag for Coverage case
3. Read the correct flag and set the DCN MPCC
pre_multiplied register bit (only on overlay plane)

Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1769Signed-off-by: Sung Joon Kim <Sungjoon.Kim@amd.com>
Reviewed-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -5381,17 +5381,19 @@ fill_plane_buffer_attributes(struct amdgpu_device *adev,
 
 static void
 fill_blending_from_plane_state(const struct drm_plane_state *plane_state,
-			       bool *per_pixel_alpha, bool *global_alpha,
-			       int *global_alpha_value)
+			       bool *per_pixel_alpha, bool *pre_multiplied_alpha,
+			       bool *global_alpha, int *global_alpha_value)
 {
 	*per_pixel_alpha = false;
+	*pre_multiplied_alpha = true;
 	*global_alpha = false;
 	*global_alpha_value = 0xff;
 
 	if (plane_state->plane->type != DRM_PLANE_TYPE_OVERLAY)
 		return;
 
-	if (plane_state->pixel_blend_mode == DRM_MODE_BLEND_PREMULTI) {
+	if (plane_state->pixel_blend_mode == DRM_MODE_BLEND_PREMULTI ||
+		plane_state->pixel_blend_mode == DRM_MODE_BLEND_COVERAGE) {
 		static const uint32_t alpha_formats[] = {
 			DRM_FORMAT_ARGB8888,
 			DRM_FORMAT_RGBA8888,
@@ -5406,6 +5408,9 @@ fill_blending_from_plane_state(const struct drm_plane_state *plane_state,
 				break;
 			}
 		}
+
+		if (per_pixel_alpha && plane_state->pixel_blend_mode == DRM_MODE_BLEND_COVERAGE)
+			*pre_multiplied_alpha = false;
 	}
 
 	if (plane_state->alpha < 0xffff) {
@@ -5568,7 +5573,7 @@ fill_dc_plane_info_and_addr(struct amdgpu_device *adev,
 		return ret;
 
 	fill_blending_from_plane_state(
-		plane_state, &plane_info->per_pixel_alpha,
+		plane_state, &plane_info->per_pixel_alpha, &plane_info->pre_multiplied_alpha,
 		&plane_info->global_alpha, &plane_info->global_alpha_value);
 
 	return 0;
@@ -5615,6 +5620,7 @@ static int fill_dc_plane_attributes(struct amdgpu_device *adev,
 	dc_plane_state->tiling_info = plane_info.tiling_info;
 	dc_plane_state->visible = plane_info.visible;
 	dc_plane_state->per_pixel_alpha = plane_info.per_pixel_alpha;
+	dc_plane_state->pre_multiplied_alpha = plane_info.pre_multiplied_alpha;
 	dc_plane_state->global_alpha = plane_info.global_alpha;
 	dc_plane_state->global_alpha_value = plane_info.global_alpha_value;
 	dc_plane_state->dcc = plane_info.dcc;
@@ -7911,7 +7917,8 @@ static int amdgpu_dm_plane_init(struct amdgpu_display_manager *dm,
 	if (plane->type == DRM_PLANE_TYPE_OVERLAY &&
 	    plane_cap && plane_cap->per_pixel_alpha) {
 		unsigned int blend_caps = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
-					  BIT(DRM_MODE_BLEND_PREMULTI);
+					  BIT(DRM_MODE_BLEND_PREMULTI) |
+					  BIT(DRM_MODE_BLEND_COVERAGE);
 
 		drm_plane_create_alpha_property(plane);
 		drm_plane_create_blend_mode_property(plane, blend_caps);

drivers/gpu/drm/amd/display/dc/core/dc_surface.c

@@ -61,6 +61,8 @@ static void dc_plane_construct(struct dc_context *ctx, struct dc_plane_state *pl
 		plane_state->blend_tf->type = TF_TYPE_BYPASS;
 	}
 
+	plane_state->pre_multiplied_alpha = true;
+
 }
 
 static void dc_plane_destruct(struct dc_plane_state *plane_state)

drivers/gpu/drm/amd/display/dc/dc.h

@@ -1011,6 +1011,7 @@ struct dc_plane_state {
 
 	bool is_tiling_rotated;
 	bool per_pixel_alpha;
+	bool pre_multiplied_alpha;
 	bool global_alpha;
 	int  global_alpha_value;
 	bool visible;
@@ -1045,6 +1046,7 @@ struct dc_plane_info {
 	bool horizontal_mirror;
 	bool visible;
 	bool per_pixel_alpha;
+	bool pre_multiplied_alpha;
 	bool global_alpha;
 	int  global_alpha_value;
 	bool input_csc_enabled;

drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c

@@ -2550,12 +2550,21 @@ void dcn10_update_mpcc(struct dc *dc, struct pipe_ctx *pipe_ctx)
 	blnd_cfg.overlap_only = false;
 	blnd_cfg.global_gain = 0xff;
 
-	if (per_pixel_alpha && pipe_ctx->plane_state->global_alpha) {
+	if (per_pixel_alpha) {
+		/* DCN1.0 has output CM before MPC which seems to screw with
+		 * pre-multiplied alpha.
+		 */
+		blnd_cfg.pre_multiplied_alpha = (is_rgb_cspace(
+				pipe_ctx->stream->output_color_space)
+						&& pipe_ctx->plane_state->pre_multiplied_alpha);
+		if (pipe_ctx->plane_state->global_alpha) {
 			blnd_cfg.alpha_mode = MPCC_ALPHA_BLEND_MODE_PER_PIXEL_ALPHA_COMBINED_GLOBAL_GAIN;
 			blnd_cfg.global_gain = pipe_ctx->plane_state->global_alpha_value;
-	} else if (per_pixel_alpha) {
+		} else {
 			blnd_cfg.alpha_mode = MPCC_ALPHA_BLEND_MODE_PER_PIXEL_ALPHA;
+		}
 	} else {
+		blnd_cfg.pre_multiplied_alpha = false;
 		blnd_cfg.alpha_mode = MPCC_ALPHA_BLEND_MODE_GLOBAL_ALPHA;
 	}
 
@@ -2564,14 +2573,6 @@ void dcn10_update_mpcc(struct dc *dc, struct pipe_ctx *pipe_ctx)
 	else
 		blnd_cfg.global_alpha = 0xff;
 
-	/* DCN1.0 has output CM before MPC which seems to screw with
-	 * pre-multiplied alpha.
-	 */
-	blnd_cfg.pre_multiplied_alpha = is_rgb_cspace(
-			pipe_ctx->stream->output_color_space)
-					&& per_pixel_alpha;
-
-
 	/*
 	 * TODO: remove hack
 	 * Note: currently there is a bug in init_hw such that

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c

@@ -2345,12 +2345,16 @@ void dcn20_update_mpcc(struct dc *dc, struct pipe_ctx *pipe_ctx)
 	blnd_cfg.overlap_only = false;
 	blnd_cfg.global_gain = 0xff;
 
-	if (per_pixel_alpha && pipe_ctx->plane_state->global_alpha) {
+	if (per_pixel_alpha) {
+		blnd_cfg.pre_multiplied_alpha = pipe_ctx->plane_state->pre_multiplied_alpha;
+		if (pipe_ctx->plane_state->global_alpha) {
 			blnd_cfg.alpha_mode = MPCC_ALPHA_BLEND_MODE_PER_PIXEL_ALPHA_COMBINED_GLOBAL_GAIN;
 			blnd_cfg.global_gain = pipe_ctx->plane_state->global_alpha_value;
-	} else if (per_pixel_alpha) {
+		} else {
 			blnd_cfg.alpha_mode = MPCC_ALPHA_BLEND_MODE_PER_PIXEL_ALPHA;
+		}
 	} else {
+		blnd_cfg.pre_multiplied_alpha = false;
 		blnd_cfg.alpha_mode = MPCC_ALPHA_BLEND_MODE_GLOBAL_ALPHA;
 	}
 
@@ -2364,7 +2368,7 @@ void dcn20_update_mpcc(struct dc *dc, struct pipe_ctx *pipe_ctx)
 	blnd_cfg.top_gain = 0x1f000;
 	blnd_cfg.bottom_inside_gain = 0x1f000;
 	blnd_cfg.bottom_outside_gain = 0x1f000;
-	blnd_cfg.pre_multiplied_alpha = per_pixel_alpha;
+
 	if (pipe_ctx->plane_state->format
 			== SURFACE_PIXEL_FORMAT_GRPH_RGBE_ALPHA)
 		blnd_cfg.pre_multiplied_alpha = false;