[PATCH v2 3/4] drm: require a non_NULL drm_crtc.primary

[Simon Ser]

If a CRTC is missing a legacy primary plane pointer, a lot of things
will be broken for user-space: fbdev stops working and the entire legacy
uAPI stops working.

Require all drivers to populate drm_crtc.primary to prevent these
issues. Warn if it's NULL.

Signed-off-by: Simon Ser <contact at emersion.fr>
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Pekka Paalanen <ppaalanen at gmail.com>
---
 drivers/gpu/drm/drm_mode_config.c | 3 +++
 drivers/gpu/drm/drm_plane.c       | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
index 2c73a60e8765..fbe680035129 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -639,6 +639,9 @@ void drm_mode_config_validate(struct drm_device *dev)
 	}
 
 	drm_for_each_crtc(crtc, dev) {
+		WARN(!crtc->primary, "Missing primary plane on [CRTC:%d:%s]\n",
+		     crtc->base.id, crtc->name);
+
 		if (crtc->primary) {
 			WARN(!(crtc->primary->possible_crtcs & BIT(crtc->index)),
 			     "Bogus primary plane possible_crtcs: [PLANE:%d:%s] must be compatible with [CRTC:%d:%s]\n",
diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index 5d33ca9f0032..49b0a8b9ac02 100644
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -57,7 +57,7 @@
  * 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
- * drivers should provide one primary plane per CRTC to avoid surprising legacy
+ * drivers must provide one primary plane per CRTC to avoid surprising legacy
  * userspace too much.
  */
 
-- 
2.29.2