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/1769
Signed-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>

5 files changed, 40 insertions, 24 deletions

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 5ea5e14b83c8..70be67a56673 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/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);
diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_surface.c b/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
index e6b9c6a71841..5bc6ff2fa73e 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
+++ b/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)
diff --git a/drivers/gpu/drm/amd/display/dc/dc.h b/drivers/gpu/drm/amd/display/dc/dc.h
index a31ea3644ec2..3960c74482be 100644
--- a/drivers/gpu/drm/amd/display/dc/dc.h
+++ b/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;
diff --git a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c
index e02ac75afbf7..e3a62873c0e7 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c
+++ b/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) {
-		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) {
-		blnd_cfg.alpha_mode = MPCC_ALPHA_BLEND_MODE_PER_PIXEL_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 {
+			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
diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c
index 0da024912dbe..ec6aa8d8b251 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c
+++ b/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) {
-		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) {
-		blnd_cfg.alpha_mode = MPCC_ALPHA_BLEND_MODE_PER_PIXEL_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 {
+			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;