[PATCH] drm: document pre-multiplied assumptions

[Simon Ser]

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

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