drm/damage-helper: Add drm_atomic_helper_damage_merged()

Useful for drivers that only care about the combined damage.

v2: Remove unnecessary clearing of damage clips

Cc: Deepak Rawat <[e-mail]>
Signed-off-by: Noralf Trønnes <[e-mail]>
Acked-by: Daniel Vetter <[e-mail]>
Reviewed-by: Sam Ravnborg <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_damage_helper.c

···
 	return ret;
 }
 EXPORT_SYMBOL(drm_atomic_helper_damage_iter_next);
+
+/**
+ * drm_atomic_helper_damage_merged - Merged plane damage
+ * @old_state: Old plane state for validation.
+ * @state: Plane state from which to iterate the damage clips.
+ * @rect: Returns the merged damage rectangle
+ *
+ * This function merges any valid plane damage clips into one rectangle and
+ * returns it in @rect.
+ *
+ * For details see: drm_atomic_helper_damage_iter_init() and
+ * drm_atomic_helper_damage_iter_next().
+ *
+ * Returns:
+ * True if there is valid plane damage otherwise false.
+ */
+bool drm_atomic_helper_damage_merged(const struct drm_plane_state *old_state,
+				     struct drm_plane_state *state,
+				     struct drm_rect *rect)
+{
+	struct drm_atomic_helper_damage_iter iter;
+	struct drm_rect clip;
+	bool valid = false;
+
+	rect->x1 = INT_MAX;
+	rect->y1 = INT_MAX;
+	rect->x2 = 0;
+	rect->y2 = 0;
+
+	drm_atomic_helper_damage_iter_init(&iter, old_state, state);
+	drm_atomic_for_each_plane_damage(&iter, &clip) {
+		rect->x1 = min(rect->x1, clip.x1);
+		rect->y1 = min(rect->y1, clip.y1);
+		rect->x2 = max(rect->x2, clip.x2);
+		rect->y2 = max(rect->y2, clip.y2);
+		valid = true;
+	}
+
+	return valid;
+}
+EXPORT_SYMBOL(drm_atomic_helper_damage_merged);

include/drm/drm_damage_helper.h

···
 bool
 drm_atomic_helper_damage_iter_next(struct drm_atomic_helper_damage_iter *iter,
 				   struct drm_rect *rect);
+bool drm_atomic_helper_damage_merged(const struct drm_plane_state *old_state,
+				     struct drm_plane_state *state,
+				     struct drm_rect *rect);
 
 /**
  * drm_helper_get_plane_damage_clips - Returns damage clips in &drm_rect.