drm: require each CRTC to have a unique primary plane

User-space expects to be able to pick a primary plane for each CRTC
exposed by the driver. Make sure this assumption holds in
drm_mode_config_validate.

Use the legacy drm_crtc.primary field to check this, because it's
simpler and we require drivers to set it anyways. Accumulate a set of
primary planes which are already used for a CRTC in a bitmask. Error out
if a primary plane is re-used.

v2: new patch

v3:
- Use u64 instead of __u64 (Jani)
- Use `unsigned int` instead of `unsigned` (Jani)

v4:
- Use u32 instead of u64 for plane mask (Ville)
- Use drm_plane_mask instead of BIT (Ville)
- Fix typos (Ville)

Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Acked-by: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Pekka Paalanen <ppaalanen@gmail.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201211184634.74534-4-contact@emersion.fr

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index 4a66374dc355..b15b65e48555 100644
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -54,6 +54,12 @@
  * enum drm_plane_type). A plane can be compatible with multiple CRTCs, see
  * &drm_plane.possible_crtcs.
  *
+ * Each CRTC must have a unique primary plane userspace can attach to enable
+ * the CRTC. In other words, userspace must be able to attach a different
+ * primary plane to each CRTC at the same time. Primary planes can still be
+ * compatible with multiple CRTCs. There must be exactly as many primary planes
+ * as there are CRTCs.
+ *
  * Legacy uAPI doesn't expose the primary and cursor planes directly. DRM core
  * relies on the driver to set the primary and optionally the cursor plane used
  * for legacy IOCTLs. This is done by calling drm_crtc_init_with_planes(). All