linux-kernel - [PATCH v2 1/2] drm/msm/dpu: simplify bg

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Message-Id: <20260112-dpu-rework-alpha-v2-1-d168785911d5@oss.qualcomm.com>
Date: Mon, 12 Jan 2026 05:23:30 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Rob Clark <robin.clark@....qualcomm.com>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Jessica Zhang <jesszhan0024@...il.com>
Cc: linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Subject: [PATCH v2 1/2] drm/msm/dpu: simplify bg_alpha selection

In order to be more obvious in fg_alpha / bg_alpha handling during the
blending programming drop the default setting for background alpha value
and set it explicitly in all cases.

Reviewed-by: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
---
 drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
index 2d06c950e814..f6827ed71f4e 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
@@ -335,13 +335,13 @@ static void _dpu_crtc_setup_blend_cfg(struct dpu_crtc_mixer *mixer,
 		max_alpha = 0x3ff;
 		fg_alpha = pstate->base.alpha >> 6;
 	}
-	bg_alpha = max_alpha - fg_alpha;
 
 	/* default to opaque blending */
 	if (pstate->base.pixel_blend_mode == DRM_MODE_BLEND_PIXEL_NONE ||
 	    !format->alpha_enable) {
 		blend_op = DPU_BLEND_FG_ALPHA_FG_CONST |
 			DPU_BLEND_BG_ALPHA_BG_CONST;
+		bg_alpha = max_alpha - fg_alpha;
 	} else if (pstate->base.pixel_blend_mode == DRM_MODE_BLEND_PREMULTI) {
 		blend_op = DPU_BLEND_FG_ALPHA_FG_CONST |
 			DPU_BLEND_BG_ALPHA_FG_PIXEL;
@@ -350,6 +350,7 @@ static void _dpu_crtc_setup_blend_cfg(struct dpu_crtc_mixer *mixer,
 			blend_op |= DPU_BLEND_BG_MOD_ALPHA |
 				    DPU_BLEND_BG_INV_MOD_ALPHA;
 		} else {
+			bg_alpha = 0;
 			blend_op |= DPU_BLEND_BG_INV_ALPHA;
 		}
 	} else {
@@ -363,6 +364,7 @@ static void _dpu_crtc_setup_blend_cfg(struct dpu_crtc_mixer *mixer,
 				    DPU_BLEND_BG_MOD_ALPHA |
 				    DPU_BLEND_BG_INV_MOD_ALPHA;
 		} else {
+			bg_alpha = 0;
 			blend_op |= DPU_BLEND_BG_INV_ALPHA;
 		}
 	}

-- 
2.47.3