media: media-entity: Simplify media_pipeline_start()

The media_pipeline_start() function has two purposes: it constructs a
pipeline by recording the entities that are part of it, gathered from a
graph walk, and validate the media links. The pipeline pointer is stored
in the media_entity structure as part of this process, and the entity's
stream count is increased, to record that the entity is streaming.

When multiple video nodes are present in a pipeline,
media_pipeline_start() is typically called on all of them, with the same
pipeline pointer. This is taken into account in media_pipeline_start()
by skipping validation for entities that are already part of the
pipeline, while returning an error if an entity is part of a different
pipeline.

It turns out that this process is overly complicated. When
media_pipeline_start() is called for the first time, it constructs the
full pipeline, adding all entities and validating all the links.
Subsequent calls to media_pipeline_start() are then nearly no-ops, they
only increase the stream count on the pipeline and on all entities.

The media_entity stream_count field is used for two purposes: checking
if the entity is streaming, and detecting when a call to
media_pipeline_stop() balances needs to reset the entity pipe pointer to
NULL. The former can easily be replaced by a check of the pipe pointer.

Simplify media_pipeline_start() by avoiding the pipeline walk on all
calls but the first one, and drop the media_entity stream_count field.
media_pipeline_stop() is updated accordingly.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
[Sakari Ailus: Drop redundant '!= NULL' as discussed]
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>

diff --git a/drivers/media/mc/mc-entity.c b/drivers/media/mc/mc-entity.c
index f83e043f0f3b14b62e89c7a65549c9c2e204b0ad..8ab0913d8d8233575b26d137ceb307721eb9ad01 100644 (file)
--- a/drivers/media/mc/mc-entity.c
+++ b/drivers/media/mc/mc-entity.c
@@ -396,20 +396,21 @@ __must_check int __media_pipeline_start(struct media_entity *entity,
        struct media_link *link;
        int ret;
 
-       if (!pipe->streaming_count++) {
-               ret = media_graph_walk_init(&pipe->graph, mdev);
-               if (ret)
-                       goto error_graph_walk_start;
+       if (pipe->streaming_count) {
+               pipe->streaming_count++;
+               return 0;
        }
 
+       ret = media_graph_walk_init(&pipe->graph, mdev);
+       if (ret)
+               return ret;
+
        media_graph_walk_start(&pipe->graph, entity);
 
        while ((entity = media_graph_walk_next(graph))) {
                DECLARE_BITMAP(active, MEDIA_ENTITY_MAX_PADS);
                DECLARE_BITMAP(has_no_links, MEDIA_ENTITY_MAX_PADS);
 
-               entity->stream_count++;
-
                if (entity->pipe && entity->pipe != pipe) {
                        pr_err("Pipe active for %s. Can't start for %s\n",
                                entity->name,
@@ -418,12 +419,12 @@ __must_check int __media_pipeline_start(struct media_entity *entity,
                        goto error;
                }
 
-               entity->pipe = pipe;
-
                /* Already streaming --- no need to check. */
-               if (entity->stream_count > 1)
+               if (entity->pipe)
                        continue;
 
+               entity->pipe = pipe;
+
                if (!entity->ops || !entity->ops->link_validate)
                        continue;
 
@@ -479,6 +480,8 @@ __must_check int __media_pipeline_start(struct media_entity *entity,
                }
        }
 
+       pipe->streaming_count++;
+
        return 0;
 
 error:
@@ -489,24 +492,17 @@ error:
        media_graph_walk_start(graph, entity_err);
 
        while ((entity_err = media_graph_walk_next(graph))) {
-               /* Sanity check for negative stream_count */
-               if (!WARN_ON_ONCE(entity_err->stream_count <= 0)) {
-                       entity_err->stream_count--;
-                       if (entity_err->stream_count == 0)
-                               entity_err->pipe = NULL;
-               }
+               entity_err->pipe = NULL;
 
                /*
-                * We haven't increased stream_count further than this
-                * so we quit here.
+                * We haven't started entities further than this so we quit
+                * here.
                 */
                if (entity_err == entity)
                        break;
        }
 
-error_graph_walk_start:
-       if (!--pipe->streaming_count)
-               media_graph_walk_cleanup(graph);
+       media_graph_walk_cleanup(graph);
 
        return ret;
 }
@@ -537,19 +533,15 @@ void __media_pipeline_stop(struct media_entity *entity)
        if (WARN_ON(!pipe))
                return;
 
+       if (--pipe->streaming_count)
+               return;
+
        media_graph_walk_start(graph, entity);
 
-       while ((entity = media_graph_walk_next(graph))) {
-               /* Sanity check for negative stream_count */
-               if (!WARN_ON_ONCE(entity->stream_count <= 0)) {
-                       entity->stream_count--;
-                       if (entity->stream_count == 0)
-                               entity->pipe = NULL;
-               }
-       }
+       while ((entity = media_graph_walk_next(graph)))
+               entity->pipe = NULL;
 
-       if (!--pipe->streaming_count)
-               media_graph_walk_cleanup(graph);
+       media_graph_walk_cleanup(graph);
 
 }
 EXPORT_SYMBOL_GPL(__media_pipeline_stop);

diff --git a/include/media/media-entity.h b/include/media/media-entity.h
index 8546f13c42a900e1a0b6bd1d3fb06b757a259bb0..33ee595c13f4602398512b4b8dceaa15fabbac0d 100644 (file)
--- a/include/media/media-entity.h
+++ b/include/media/media-entity.h
@@ -268,7 +268,6 @@ enum media_entity_type {
  * @pads:      Pads array with the size defined by @num_pads.
  * @links:     List of data links.
  * @ops:       Entity operations.
- * @stream_count: Stream count for the entity.
  * @use_count: Use count for the entity.
  * @pipe:      Pipeline this entity belongs to.
  * @info:      Union with devnode information.  Kept just for backward
@@ -283,10 +282,9 @@ enum media_entity_type {
  *
  * .. note::
  *
- *    @stream_count and @use_count reference counts must never be
- *    negative, but are signed integers on purpose: a simple ``WARN_ON(<0)``
- *    check can be used to detect reference count bugs that would make them
- *    negative.
+ *    The @use_count reference count must never be negative, but is a signed
+ *    integer on purpose: a simple ``WARN_ON(<0)`` check can be used to detect
+ *    reference count bugs that would make it negative.
  */
 struct media_entity {
        struct media_gobj graph_obj;    /* must be first field in struct */
@@ -305,7 +303,6 @@ struct media_entity {
 
        const struct media_entity_operations *ops;
 
-       int stream_count;
        int use_count;
 
        struct media_pipeline *pipe;
@@ -867,7 +864,7 @@ struct media_pad *media_entity_remote_pad(const struct media_pad *pad);
  */
 static inline bool media_entity_is_streaming(const struct media_entity *entity)
 {
-       return entity->stream_count > 0;
+       return entity->pipe;
 }
 
 /**