[PATCH v2 4/4] drm: require each CRTC to have a unique primary plane

[Simon Ser <contact@xxxxxxxxxxx>]

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.

Signed-off-by: Simon Ser <contact@xxxxxxxxxxx>
Cc: Daniel Vetter <daniel@xxxxxxxx>
Cc: Pekka Paalanen <ppaalanen@xxxxxxxxx>
---
 drivers/gpu/drm/drm_mode_config.c | 21 +++++++++++++++++++++
 drivers/gpu/drm/drm_plane.c       |  6 ++++++
 2 files changed, 27 insertions(+)

diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
index fbe680035129..f143f56f0820 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -626,6 +626,9 @@ void drm_mode_config_validate(struct drm_device *dev)
 {
 	struct drm_encoder *encoder;
 	struct drm_crtc *crtc;
+	struct drm_plane *plane;
+	__u64 primary_with_crtc = 0, cursor_with_crtc = 0;
+	unsigned num_primary = 0;
 
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		return;
@@ -647,12 +650,30 @@ void drm_mode_config_validate(struct drm_device *dev)
 			     "Bogus primary plane possible_crtcs: [PLANE:%d:%s] must be compatible with [CRTC:%d:%s]\n",
 			     crtc->primary->base.id, crtc->primary->name,
 			     crtc->base.id, crtc->name);
+			WARN(primary_with_crtc & BIT(crtc->primary->index),
+			     "Primary plane [PLANE:%d:%s] used for two CRTCs",
+			     crtc->primary->base.id, crtc->primary->name);
+			primary_with_crtc |= BIT(crtc->primary->index);
 		}
 		if (crtc->cursor) {
 			WARN(!(crtc->cursor->possible_crtcs & BIT(crtc->index)),
 			     "Bogus cursor plane possible_crtcs: [PLANE:%d:%s] must be compatible with [CRTC:%d:%s]\n",
 			     crtc->cursor->base.id, crtc->cursor->name,
 			     crtc->base.id, crtc->name);
+			WARN(cursor_with_crtc & BIT(crtc->cursor->index),
+			     "Primary plane [PLANE:%d:%s] used for two CRTCs",
+			     crtc->cursor->base.id, crtc->cursor->name);
+			cursor_with_crtc |= BIT(crtc->cursor->index);
 		}
 	}
+
+	drm_for_each_plane(plane, dev) {
+		if (plane->type == DRM_PLANE_TYPE_PRIMARY) {
+			num_primary++;
+		}
+	}
+
+	WARN(num_primary != dev->mode_config.num_crtc,
+	     "Must have as many primary planes as there are CRTCs, but have %u primary planes and %u CRTCs",
+	     num_primary, dev->mode_config.num_crtc);
 }
diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index 49b0a8b9ac02..a1f4510efa83 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
-- 
2.29.2


_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/dri-devel