[PATCH v2] drm/doc: document front-buffer rendering

[Simon Ser]

Explain how to perform front-buffer rendering.

v2: apply Pekka's rewrite

Signed-off-by: Simon Ser <contact at emersion.fr>
Cc: Pekka Paalanen <pekka.paalanen at collabora.com>
Cc: Simona Vetter <simona.vetter at ffwll.ch>
---
 drivers/gpu/drm/drm_blend.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
index 6e74de833466..4e83f372ea51 100644
--- a/drivers/gpu/drm/drm_blend.c
+++ b/drivers/gpu/drm/drm_blend.c
@@ -75,6 +75,12 @@
  * 	the currently visible vertical area of the &drm_crtc.
  * FB_ID:
  * 	Mode object ID of the &drm_framebuffer this plane should scan out.
+ *
+ *	When a KMS client is perfoming front-buffer rendering, it should set
+ *	FB_ID to the same front-buffer FB on each atomic commit. This implies
+ *	to the driver that it needs to re-read the same FB again. Otherwise
+ *	drivers which do not employ continuously repeated scanout cycles might
+ *	not update the screen.
  * CRTC_ID:
  * 	Mode object ID of the &drm_crtc this plane should be connected to.
  *
-- 
2.49.0