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media: media-entity: Simplify media_pipeline_start()

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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>
This commit is contained in:
Laurent Pinchart 2022-01-13 17:00:42 +02:00 committed by Sakari Ailus
parent f17bc788f7
commit 3056a8e936
2 changed files with 26 additions and 37 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

42
drivers/media/mc/mc-entity.c
View File

@ -396,11 +396,14 @@ __must_check int __media_pipeline_start(struct media_entity *entity,
struct media_link *link;
int ret;
if (!pipe->streaming_count++) {
if (pipe->streaming_count) {
pipe->streaming_count++;
return 0;
}
ret = media_graph_walk_init(&pipe->graph, mdev);
if (ret)
goto error_graph_walk_start;
}
return ret;
media_graph_walk_start(&pipe->graph, entity);
@ -408,8 +411,6 @@ __must_check int __media_pipeline_start(struct media_entity *entity,
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:
@ -489,23 +492,16 @@ 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;
}
/*
* 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);
return ret;
@ -537,18 +533,14 @@ 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)
while ((entity = media_graph_walk_next(graph)))
entity->pipe = NULL;
}
}
if (!--pipe->streaming_count)
media_graph_walk_cleanup(graph);
}

11
include/media/media-entity.h
View File

@ -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;
}
/**