[media] media: entity: Catch unbalanced media_pipeline_stop calls

Drivers must not perform unbalanced calls to stop the entity pipeline,
however if they do they will fault in the core media code, as the
entity->pipe will be set as NULL. We handle this gracefully in the core
with a WARN for the developer.

Replace the erroneous check on zero streaming counts, with a check on
NULL pipe elements instead, as this is the symptom of unbalanced
media_pipeline_stop calls.
Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pincharts@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/media-entity.c

@@ -566,8 +566,13 @@ void __media_pipeline_stop(struct media_entity *entity)
 	struct media_graph *graph = &entity->pipe->graph;
 	struct media_pipeline *pipe = entity->pipe;
 
+	/*
+	 * If the following check fails, the driver has performed an
+	 * unbalanced call to media_pipeline_stop()
+	 */
+	if (WARN_ON(!pipe))
+		return;
 
-	WARN_ON(!pipe->streaming_count);
 	media_graph_walk_start(graph, entity);
 
 	while ((entity = media_graph_walk_next(graph))) {