Hi Sakari,
On Sat, Jan 15, 2022 at 07:39:33PM +0200, Sakari Ailus wrote:
> Moi,
>
> Thanks for the set.
Ole hyvä.
> On Thu, Jan 13, 2022 at 05:00:42PM +0200, Laurent Pinchart wrote:
> > From: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxxxxx>
> > ---
> > drivers/media/mc/mc-entity.c | 52 +++++++++++++++---------------------
> > include/media/media-entity.h | 11 +++-----
> > 2 files changed, 26 insertions(+), 37 deletions(-)
> >
> > diff --git a/drivers/media/mc/mc-entity.c b/drivers/media/mc/mc-entity.c
> > index f83e043f0f3b..8ab0913d8d82 100644
> > --- 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 @@ __must_check int __media_pipeline_start(struct media_entity *entity,
> > 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 8546f13c42a9..e3c4fd1e3623 100644
> > --- 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 != NULL;
>
> I'd drop "!= NULL" part; it's redundant.
I usually use "if (pointer)" or "if (!pointer)" without comparing to
NULL, but for some reason, when returning a bool, it feels more explicit
to me to use a comparison. I'm not sure why, maybe because, unlike with
if (), the implicit cast is only apparent when you read the signature of
the function ? Not that it's far away in this case, it's only two lines
up.
> I'll do that when applying if that's fine.
Fine with me, I don't mind either way. Thanks.
> > }
> >
> > /**
--
Regards,
Laurent Pinchart
