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drm/vc4: hvs6: Fix plane alpha with Pre-multiplied and None blend modes - #7703
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popcornmix wants to merge 2 commits into
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…alpha On BCM2712 D0, a format with no alpha channel takes its alpha from the plane alpha property (ALPHA_MASK_FIXED). With the default "Pre-multiplied" blend mode the ALPHA_PREMULT flag was still set, so the HVS treated the colour as already multiplied by the plane alpha and added it unscaled on top of the planes below. The KMS blend modes are all equivalent when there is no pixel alpha, so only set ALPHA_PREMULT when the format has an alpha channel, as the other generations already do. Fixes: raspberrypi#7700 Signed-off-by: Dom Cobley <popcornmix@gmail.com>
With the "None" pixel blend mode the HVS takes the plane alpha property as a fixed alpha. For a format with an alpha channel ALPHA_MIX was also set, multiplying the plane alpha in a second time, so a plane alpha of 0.5 blended at 0.25. Seen on both BCM2712 C1 and D0. Don't set ALPHA_MIX when the blend mode is "None". Signed-off-by: Dom Cobley <popcornmix@gmail.com>
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Two plane alpha bugs on BCM2712:
ALPHA_PREMULT, so the plane was added unfaded on top of the planes below.Tested by capturing through writeback on Pi 500 (D0, 7.3 kernel) and Pi 5 (C1, 6.18.57 kernel): with plane alpha 0.5, every blend mode on XRGB8888 and on ARGB8888 (pixel alpha 0xff, 0x80, 0x00) now matches the formulas in
drm_blend.c.Fixes #7700