1 files changed, 37 insertions, 0 deletions

diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
index 2095917ff8c7..a0ea4ded3cb5 100644
--- a/include/drm/drm_atomic_helper.h
+++ b/include/drm/drm_atomic_helper.h
@@ -127,4 +127,41 @@ void drm_atomic_helper_connector_destroy_state(struct drm_connector *connector,
 #define drm_atomic_crtc_state_for_each_plane(plane, crtc_state) \
         drm_for_each_plane_mask(plane, (crtc_state)->state->dev, (crtc_state)->plane_mask)
 
+/*
+ * drm_atomic_plane_disabling - check whether a plane is being disabled
+ * @plane: plane object
+ * @old_state: previous atomic state
+ *
+ * Checks the atomic state of a plane to determine whether it's being disabled
+ * or not. This also WARNs if it detects an invalid state (both CRTC and FB
+ * need to either both be NULL or both be non-NULL).
+ *
+ * RETURNS:
+ * True if the plane is being disabled, false otherwise.
+ */
+static inline bool
+drm_atomic_plane_disabling(struct drm_plane *plane,
+                           struct drm_plane_state *old_state)
+{
+        /*
+         * When disabling a plane, CRTC and FB should always be NULL together.
+         * Anything else should be considered a bug in the atomic core, so we
+         * gently warn about it.
+         */
+        WARN_ON((plane->state->crtc == NULL && plane->state->fb != NULL) ||
+                (plane->state->crtc != NULL && plane->state->fb == NULL));
+
+        /*
+         * When using the transitional helpers, old_state may be NULL. If so,
+         * we know nothing about the current state and have to assume that it
+         * might be enabled.
+         *
+         * When using the atomic helpers, old_state won't be NULL. Therefore
+         * this check assumes that either the driver will have reconstructed
+         * the correct state in ->reset() or that the driver will have taken
+         * appropriate measures to disable all planes.
+         */
+        return (!old_state || old_state->crtc) && !plane->state->crtc;
+}
+
 #endif /* DRM_ATOMIC_HELPER_H_ */