[media] media: Keep using the same graph walk object for a given pipeline

Initialise a given graph walk object once, and then keep using it whilst
the same pipeline is running. Once the pipeline is stopped, release the
graph walk object.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/media-entity.c

@@ -379,10 +379,10 @@ __must_check int media_entity_pipeline_start(struct media_entity *entity,
 
 	mutex_lock(&mdev->graph_mutex);
 
-	ret = media_entity_graph_walk_init(&pipe->graph, mdev);
-	if (ret) {
-		mutex_unlock(&mdev->graph_mutex);
-		return ret;
+	if (!pipe->streaming_count++) {
+		ret = media_entity_graph_walk_init(&pipe->graph, mdev);
+		if (ret)
+			goto error_graph_walk_start;
 	}
 
 	media_entity_graph_walk_start(&pipe->graph, entity);
@@ -483,7 +483,9 @@ __must_check int media_entity_pipeline_start(struct media_entity *entity,
 			break;
 	}
 
-	media_entity_graph_walk_cleanup(graph);
+error_graph_walk_start:
+	if (!--pipe->streaming_count)
+		media_entity_graph_walk_cleanup(graph);
 
 	mutex_unlock(&mdev->graph_mutex);
 
@@ -495,9 +497,11 @@ void media_entity_pipeline_stop(struct media_entity *entity)
 {
 	struct media_device *mdev = entity->graph_obj.mdev;
 	struct media_entity_graph *graph = &entity->pipe->graph;
+	struct media_pipeline *pipe = entity->pipe;
 
 	mutex_lock(&mdev->graph_mutex);
 
+	WARN_ON(!pipe->streaming_count);
 	media_entity_graph_walk_start(graph, entity);
 
 	while ((entity = media_entity_graph_walk_next(graph))) {
@@ -506,7 +510,8 @@ void media_entity_pipeline_stop(struct media_entity *entity)
 			entity->pipe = NULL;
 	}
 
-	media_entity_graph_walk_cleanup(graph);
+	if (!--pipe->streaming_count)
+		media_entity_graph_walk_cleanup(graph);
 
 	mutex_unlock(&mdev->graph_mutex);
 }

include/media/media-entity.h

@@ -119,9 +119,11 @@ struct media_entity_graph {
 /*
  * struct media_pipeline - Media pipeline related information
  *
- * @graph:	Media graph walk during pipeline start / stop
+ * @streaming_count:	Streaming start count - streaming stop count
+ * @graph:		Media graph walk during pipeline start / stop
  */
 struct media_pipeline {
+	int streaming_count;
 	struct media_entity_graph graph;
 };