[media] media: Pipelines and media streams

Drivers often need to associate pipeline objects to entities, and to
take stream state into account when configuring entities and links. The
pipeline API helps drivers manage that information.

When starting streaming, drivers call media_entity_pipeline_start(). The
function marks all entities connected to the given entity through
enabled links, either directly or indirectly, as streaming. Similarly,
when stopping the stream, drivers call media_entity_pipeline_stop().

The media_entity_pipeline_start() function takes a pointer to a media
pipeline and stores it in every entity in the graph. Drivers should
embed the media_pipeline structure in higher-level pipeline structures
and can then access the pipeline through the media_entity structure.

Link configuration will fail with -EBUSY by default if either end of the
link is a streaming entity, unless the link is marked with the
MEDIA_LNK_FL_DYNAMIC flag.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 73 insertions, 0 deletions

diff --git a/drivers/media/media-entity.c b/drivers/media/media-entity.c
index 6795c92..23640ed 100644
--- a/drivers/media/media-entity.c
+++ b/drivers/media/media-entity.c
@@ -197,6 +197,75 @@ media_entity_graph_walk_next(struct media_entity_graph *graph)
 EXPORT_SYMBOL_GPL(media_entity_graph_walk_next);
 
 /* -----------------------------------------------------------------------------
+ * Pipeline management
+ */
+
+/**
+ * media_entity_pipeline_start - Mark a pipeline as streaming
+ * @entity: Starting entity
+ * @pipe: Media pipeline to be assigned to all entities in the pipeline.
+ *
+ * Mark all entities connected to a given entity through enabled links, either
+ * directly or indirectly, as streaming. The given pipeline object is assigned to
+ * every entity in the pipeline and stored in the media_entity pipe field.
+ *
+ * Calls to this function can be nested, in which case the same number of
+ * media_entity_pipeline_stop() calls will be required to stop streaming. The
+ * pipeline pointer must be identical for all nested calls to
+ * media_entity_pipeline_start().
+ */
+void media_entity_pipeline_start(struct media_entity *entity,
+				 struct media_pipeline *pipe)
+{
+	struct media_device *mdev = entity->parent;
+	struct media_entity_graph graph;
+
+	mutex_lock(&mdev->graph_mutex);
+
+	media_entity_graph_walk_start(&graph, entity);
+
+	while ((entity = media_entity_graph_walk_next(&graph))) {
+		entity->stream_count++;
+		WARN_ON(entity->pipe && entity->pipe != pipe);
+		entity->pipe = pipe;
+	}
+
+	mutex_unlock(&mdev->graph_mutex);
+}
+EXPORT_SYMBOL_GPL(media_entity_pipeline_start);
+
+/**
+ * media_entity_pipeline_stop - Mark a pipeline as not streaming
+ * @entity: Starting entity
+ *
+ * Mark all entities connected to a given entity through enabled links, either
+ * directly or indirectly, as not streaming. The media_entity pipe field is
+ * reset to NULL.
+ *
+ * If multiple calls to media_entity_pipeline_start() have been made, the same
+ * number of calls to this function are required to mark the pipeline as not
+ * streaming.
+ */
+void media_entity_pipeline_stop(struct media_entity *entity)
+{
+	struct media_device *mdev = entity->parent;
+	struct media_entity_graph graph;
+
+	mutex_lock(&mdev->graph_mutex);
+
+	media_entity_graph_walk_start(&graph, entity);
+
+	while ((entity = media_entity_graph_walk_next(&graph))) {
+		entity->stream_count--;
+		if (entity->stream_count == 0)
+			entity->pipe = NULL;
+	}
+
+	mutex_unlock(&mdev->graph_mutex);
+}
+EXPORT_SYMBOL_GPL(media_entity_pipeline_stop);
+
+/* -----------------------------------------------------------------------------
  * Module use count
  */
 
@@ -364,6 +433,10 @@ int __media_entity_setup_link(struct media_link *link, u32 flags)
 	source = link->source->entity;
 	sink = link->sink->entity;
 
+	if (!(link->flags & MEDIA_LNK_FL_DYNAMIC) &&
+	    (source->stream_count || sink->stream_count))
+		return -EBUSY;
+
 	mdev = source->parent;
 
 	if ((flags & MEDIA_LNK_FL_ENABLED) && mdev->link_notify) {