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Commit f616ecec authored by Melissa Wen's avatar Melissa Wen Committed by Greg Kroah-Hartman
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drm/amd/display: don't ignore alpha property on pre-multiplied mode 

commit e4f1541caf60fcbe5a59e9d25805c0b5865e546a upstream.

"Pre-multiplied" is the default pixel blend mode for KMS/DRM, as
documented in supported_modes of drm_plane_create_blend_mode_property():
https://cgit.freedesktop.org/drm/drm-misc/tree/drivers/gpu/drm/drm_blend.c

In this mode, both 'pixel alpha' and 'plane alpha' participate in the
calculation, as described by the pixel blend mode formula in KMS/DRM
documentation:

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

Considering the blend config mechanisms we have in the driver so far,
the alpha mode that better fits this blend mode is the
_PER_PIXEL_ALPHA_COMBINED_GLOBAL_GAIN, where the value for global_gain
is the plane alpha (global_alpha).

With this change, alpha property stops to be ignored. It also addresses
Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1734



v2:
 * keep the 8-bit value for global_alpha_value (Nicholas)
 * correct the logical ordering for combined global gain (Nicholas)
 * apply to dcn10 too (Nicholas)

Signed-off-by: default avatarMelissa Wen <mwen@igalia.com>
Tested-by: default avatarRodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Reviewed-by: default avatarHarry Wentland <harry.wentland@amd.com>
Tested-by: default avatarSimon Ser <contact@emersion.fr>
Signed-off-by: default avatarAlex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent ab2f5afb

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

+9 −5
Original line number Diff line number Diff line
@@ -2202,14 +2202,18 @@ static void dcn10_update_mpcc(struct dc *dc, struct pipe_ctx *pipe_ctx) 
				&blnd_cfg.black_color);

	}



	if (per_pixel_alpha)

		blnd_cfg.alpha_mode = MPCC_ALPHA_BLEND_MODE_PER_PIXEL_ALPHA;

	else

		blnd_cfg.alpha_mode = MPCC_ALPHA_BLEND_MODE_GLOBAL_ALPHA;



	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;

	} else {

		blnd_cfg.alpha_mode = MPCC_ALPHA_BLEND_MODE_GLOBAL_ALPHA;

	}



	if (pipe_ctx->plane_state->global_alpha)

		blnd_cfg.global_alpha = pipe_ctx->plane_state->global_alpha_value;

	else

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

+9 −5
Original line number Diff line number Diff line
@@ -1740,14 +1740,18 @@ static void dcn20_update_mpcc(struct dc *dc, struct pipe_ctx *pipe_ctx) 
				pipe_ctx, &blnd_cfg.black_color);

	}



	if (per_pixel_alpha)

		blnd_cfg.alpha_mode = MPCC_ALPHA_BLEND_MODE_PER_PIXEL_ALPHA;

	else

		blnd_cfg.alpha_mode = MPCC_ALPHA_BLEND_MODE_GLOBAL_ALPHA;



	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;

	} else {

		blnd_cfg.alpha_mode = MPCC_ALPHA_BLEND_MODE_GLOBAL_ALPHA;

	}



	if (pipe_ctx->plane_state->global_alpha)

		blnd_cfg.global_alpha = pipe_ctx->plane_state->global_alpha_value;

	else