2 files changed, 58 insertions, 2 deletions
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index 92c84e9ab09a..4e97186293be 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -109,6 +109,42 @@ drm_atomic_get_existing_connector_state(struct drm_atomic_state *state,
 	return state->connector_states[index];
 }
 
+/**
+ * __drm_atomic_get_current_plane_state - get current plane state
+ * @state: global atomic state object
+ * @plane: plane to grab
+ *
+ * This function returns the plane state for the given plane, either from
+ * @state, or if the plane isn't part of the atomic state update, from @plane.
+ * This is useful in atomic check callbacks, when drivers need to peek at, but
+ * not change, state of other planes, since it avoids threading an error code
+ * back up the call chain.
+ *
+ * WARNING:
+ *
+ * Note that this function is in general unsafe since it doesn't check for the
+ * required locking for access state structures. Drivers must ensure that it is
+ * save to access the returned state structure through other means. One commone
+ * example is when planes are fixed to a single CRTC, and the driver knows that
+ * the CRTC locks is held already. In that case holding the CRTC locks gives a
+ * read-lock on all planes connected to that CRTC. But if planes can be
+ * reassigned things get more tricky. In that case it's better to use
+ * drm_atomic_get_plane_state and wire up full error handling.
+ *
+ * Returns:
+ *
+ * Read-only pointer to the current plane state.
+ */
+static inline const struct drm_plane_state *
+__drm_atomic_get_current_plane_state(struct drm_atomic_state *state,
+				     struct drm_plane *plane)
+{
+	if (state->plane_states[drm_plane_index(plane)])
+		return state->plane_states[drm_plane_index(plane)];
+
+	return plane->state;
+}
+
 int __must_check
 drm_atomic_set_mode_for_crtc(struct drm_crtc_state *state,
 			     struct drm_display_mode *mode);
diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
index d473dcc91f54..b03bd83703b4 100644
--- a/include/drm/drm_atomic_helper.h
+++ b/include/drm/drm_atomic_helper.h
@@ -159,7 +159,7 @@ void drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
  * This iterates over the current state, useful (for example) when applying
  * atomic state after it has been checked and swapped.  To iterate over the
  * planes which *will* be attached (for ->atomic_check()) see
- * drm_crtc_for_each_pending_plane()
+ * drm_crtc_for_each_pending_plane().
  */
 #define drm_atomic_crtc_for_each_plane(plane, crtc) \
 	drm_for_each_plane_mask(plane, (crtc)->dev, (crtc)->state->plane_mask)
@@ -171,11 +171,31 @@ void drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
  *
  * Similar to drm_crtc_for_each_plane(), but iterates the planes that will be
  * attached if the specified state is applied.  Useful during (for example)
- * ->atomic_check() operations, to validate the incoming state
+ * ->atomic_check() operations, to validate the incoming state.
  */
 #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_crtc_atomic_state_for_each_plane_state - iterate over attached planes in new state
+ * @plane: the loop cursor
+ * @plane_state: loop cursor for the plane's state, must be const
+ * @crtc_state: the incoming crtc-state
+ *
+ * Similar to drm_crtc_for_each_plane(), but iterates the planes that will be
+ * attached if the specified state is applied.  Useful during (for example)
+ * ->atomic_check() operations, to validate the incoming state.
+ *
+ * Compared to just drm_atomic_crtc_state_for_each_plane() this also fills in a
+ * const plane_state. This is useful when a driver just wants to peek at other
+ * active planes on this crtc, but does not need to change it.
+ */
+#define drm_atomic_crtc_state_for_each_plane_state(plane, plane_state, crtc_state) \
+	drm_for_each_plane_mask(plane, (crtc_state)->state->dev, (crtc_state)->plane_mask) \
+		for_each_if ((plane_state = \
+			      __drm_atomic_get_current_plane_state((crtc_state)->state, \
+								   plane)))
+
 /*
  * drm_atomic_plane_disabling - check whether a plane is being disabled
  * @plane: plane object