Re: [PATCH] drm: document pre-multiplied assumptions

On Wed, Sep 29, 2021 at 09:54:14AM +0000, Simon Ser wrote:

When a plane is missing the "alpha blend mode" property, KMS drivers will use the pre-multiplied mode.

Signed-off-by: Simon Ser contact@emersion.fr Cc: Daniel Vetter daniel@ffwll.ch Cc: Pekka Paalanen ppaalanen@gmail.com

Reviewed-by: Ville Syrjälä ville.syrjala@linux.intel.com

Another option would be to sprinkle immutable props to all drivers that claim to do alpha blending and don't currently expose the property.

---

drivers/gpu/drm/drm_blend.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c index ec37cbfabb50..eebb32ba84d7 100644 --- a/drivers/gpu/drm/drm_blend.c +++ b/drivers/gpu/drm/drm_blend.c @@ -185,6 +185,9 @@

•  plane does not expose the "alpha" property, then this is
  

•  assumed to be 1.0
  

• • When a plane is missing this property, the plane uses the
• • "Pre-multiplied" equation.
• • Note that all the property extensions described here apply either to the
  • plane or the CRTC (e.g. for the background color, which currently is not
  • exposed and assumed to be black).

-- 2.33.0