drm/sun4i: Add TODO comment about supporting scaling with the backend

The backend allows integer-only scaling but can handle alpha components,
unlike the frontend. It could be useful to add support for this
eventually, so add a short TODO comment describing the situation.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181123092515.2511-4-paul.kocialkowski@bootlin.com

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c b/drivers/gpu/drm/sun4i/sun4i_backend.c
index 67b4bb4f5365..c3444246755b 100644
--- a/drivers/gpu/drm/sun4i/sun4i_backend.c
+++ b/drivers/gpu/drm/sun4i/sun4i_backend.c
@@ -426,6 +426,11 @@ static bool sun4i_backend_plane_uses_frontend(struct drm_plane_state *state)
         if (IS_ERR(backend->frontend))
                 return false;
 
+        /*
+         * TODO: The backend alone allows 2x and 4x integer scaling, including
+         * support for an alpha component (which the frontend doesn't support).
+         * Use the backend directly instead of the frontend in this case.
+         */
         return sun4i_backend_plane_uses_scaler(state);
 }