6.10-stable review patch. If anyone has any objections, please let me know.
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From: Hsiao Chien Sung shawn.sung@mediatek.com
[ Upstream commit 31c0fbf67c8c0bb38d7fb21d404ea3dbd619d99e ]
The formula of Coverage alpha blending is: dst.a = dst.a * (0xff - src.a * SCA / 0xff) / 0xff + src.a * SCA / 0xff
dst.a: destination alpha src.a: pixel alpha SCA : plane alpha
When SCA = 0xff, the formula becomes: dst.a = dst.a * (0xff - src.a) + src.a
This patch is to set the destination alpha (background) to 0xff: - When dst.a = 0 (before), dst.a = src.a - When dst.a = 0xff (after) , dst.a = 0xff * (0xff - src.a) + src.a
According to the fomula above: - When src.a = 0 , dst.a = 0 - When src.a = 0xff, dst.a = 0xff This two cases are just still correct. But when src.a is between 0 and 0xff, the difference starts to appear
Fixes: 616443ca577e ("drm/mediatek: Move cmdq_reg info from struct mtk_ddp_comp to sub driver private data") Signed-off-by: Hsiao Chien Sung shawn.sung@mediatek.com Link: https://patchwork.kernel.org/project/dri-devel/patch/20240620-igt-v3-5-a9d62... Signed-off-by: Chun-Kuang Hu chunkuang.hu@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/mediatek/mtk_disp_ovl.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/mediatek/mtk_disp_ovl.c b/drivers/gpu/drm/mediatek/mtk_disp_ovl.c index bd00e5e85deba..693560fa34e8b 100644 --- a/drivers/gpu/drm/mediatek/mtk_disp_ovl.c +++ b/drivers/gpu/drm/mediatek/mtk_disp_ovl.c @@ -72,6 +72,8 @@ #define OVL_CON_VIRT_FLIP BIT(9) #define OVL_CON_HORZ_FLIP BIT(10)
+#define OVL_COLOR_ALPHA GENMASK(31, 24) + static const u32 mt8173_formats[] = { DRM_FORMAT_XRGB8888, DRM_FORMAT_ARGB8888, @@ -274,7 +276,13 @@ void mtk_ovl_config(struct device *dev, unsigned int w, if (w != 0 && h != 0) mtk_ddp_write_relaxed(cmdq_pkt, h << 16 | w, &ovl->cmdq_reg, ovl->regs, DISP_REG_OVL_ROI_SIZE); - mtk_ddp_write_relaxed(cmdq_pkt, 0x0, &ovl->cmdq_reg, ovl->regs, DISP_REG_OVL_ROI_BGCLR); + + /* + * The background color must be opaque black (ARGB), + * otherwise the alpha blending will have no effect + */ + mtk_ddp_write_relaxed(cmdq_pkt, OVL_COLOR_ALPHA, &ovl->cmdq_reg, + ovl->regs, DISP_REG_OVL_ROI_BGCLR);
mtk_ddp_write(cmdq_pkt, 0x1, &ovl->cmdq_reg, ovl->regs, DISP_REG_OVL_RST); mtk_ddp_write(cmdq_pkt, 0x0, &ovl->cmdq_reg, ovl->regs, DISP_REG_OVL_RST);