Re: [PATCH v3 15/33] media: Add link_validate() op to check links to the sink pad

Laurent Pinchart
2012-02-22T10:05:04Z

Hi Sakari,

Thanks for the patch.

On Monday 20 February 2012 03:56:54 Sakari Ailus wrote:
> The purpose of the link_validate() op is to allow an entity driver to ensure
> that the properties of the pads at the both ends of the link are suitable
> for starting the pipeline. link_validate is called on sink pads on active
> links which belong to the active part of the graph.
>
> Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
> ---
> Documentation/media-framework.txt | 19 +++++++++++++
> drivers/media/media-entity.c | 53
> +++++++++++++++++++++++++++++++++++- include/media/media-entity.h |
> 5 ++-
> 3 files changed, 73 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/media-framework.txt
> b/Documentation/media-framework.txt index 3a0f879..0e90169 100644
> --- a/Documentation/media-framework.txt
> +++ b/Documentation/media-framework.txt
> @@ -335,6 +335,9 @@ the media_entity pipe field.
> Calls to media_entity_pipeline_start() can be nested. The pipeline pointer
> must be identical for all nested calls to the function.
>
> +media_entity_pipeline_start() may return an error. In that case, it will
> +clean up any the changes it did by itself.
> +
> When stopping the stream, drivers must notify the entities with
>
> media_entity_pipeline_stop(struct media_entity *entity);
> @@ -351,3 +354,19 @@ If other operations need to be disallowed on streaming
> entities (such as changing entities configuration parameters) drivers can
> explicitly check the media_entity stream_count field to find out if an
> entity is streaming. This operation must be done with the media_device
> graph_mutex held.
> +
> +
> +Link validation
> +---------------
> +
> +Link validation is performed from media_entity_pipeline_start() for any

s/from/by/ ?

> +entity which has sink pads in the pipeline. The
> +media_entity::link_validate() callback is used for that purpose. In
> +link_validate() callback, entity driver should check that the properties of
> +the source pad of the connected entity and its own sink pad match. It is up
> +to the type of the entity (and in the end, the properties of the hardware)
> +what matching actually means.
> +
> +Subsystems should facilitate link validation by providing subsystem
> specific
> +helper functions to provide easy access for commonly needed information,
> and
> +in the end provide a way to use driver-specific callbacks.
> diff --git a/drivers/media/media-entity.c b/drivers/media/media-entity.c
> index 056138f..678ec07 100644
> --- a/drivers/media/media-entity.c
> +++ b/drivers/media/media-entity.c
> @@ -214,23 +214,72 @@ EXPORT_SYMBOL_GPL(media_entity_graph_walk_next);
> * 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)
> +__must_check int media_entity_pipeline_start(struct media_entity *entity,
> + struct media_pipeline *pipe)
> {
> struct media_device *mdev = entity->parent;
> struct media_entity_graph graph;
> + struct media_entity *entity_err = entity;
> + int ret = 0;
>
> mutex_lock(&mdev->graph_mutex);
>
> media_entity_graph_walk_start(&graph, entity);
>
> while ((entity = media_entity_graph_walk_next(&graph))) {
> + int i;
> +

entity->num_link is unsigned, what about making i an unsigned int ?

> entity->stream_count++;
> WARN_ON(entity->pipe && entity->pipe != pipe);
> entity->pipe = pipe;
> +
> + /* Already streaming --- no need to check. */
> + if (entity->stream_count > 1)
> + continue;
> +
> + if (!entity->ops || !entity->ops->link_validate)
> + continue;
> +
> + for (i = 0; i < entity->num_links; i++) {
> + struct media_link *link = &entity->links[i];
> +
> + /* Is this pad part of an enabled link? */
> + if ((link->flags & MEDIA_LNK_FL_ENABLED)
> + != MEDIA_LNK_FL_ENABLED)

Just nickpicking, if you wrote it

if (!(link->flags & MEDIA_LNK_FL_ENABLED))

it would fit on a single line :-)

> + continue;
> +
> + /* Are we the sink or not? */
> + if (link->sink->entity != entity)
> + continue;
> +
> + ret = entity->ops->link_validate(link);
> + if (ret < 0 && ret != -ENOIOCTLCMD)
> + break;

You could goto error directly here, this would avoid checking the ret value
after the loop, and you could also avoid initializing ret to 0.

> + }
> + if (ret < 0 && ret != -ENOIOCTLCMD)
> + goto error;
> }
>
> mutex_unlock(&mdev->graph_mutex);
> +
> + return 0;
> +
> +error:
> + /*
> + * Link validation on graph failed. We revert what we did and
> + * return the error.
> + */
> + media_entity_graph_walk_start(&graph, entity_err);
> + do {
> + entity_err = media_entity_graph_walk_next(&graph);
> + entity_err->stream_count--;
> + if (entity_err->stream_count == 0)
> + entity_err->pipe = NULL;
> + } while (entity_err != entity);
> +
> + mutex_unlock(&mdev->graph_mutex);
> +
> + return ret;
> }
> EXPORT_SYMBOL_GPL(media_entity_pipeline_start);
>
> diff --git a/include/media/media-entity.h b/include/media/media-entity.h
> index 29e7bba..0c16f51 100644
> --- a/include/media/media-entity.h
> +++ b/include/media/media-entity.h
> @@ -46,6 +46,7 @@ struct media_entity_operations {
> int (*link_setup)(struct media_entity *entity,
> const struct media_pad *local,
> const struct media_pad *remote, u32 flags);
> + int (*link_validate)(struct media_link *link);
> };
>
> struct media_entity {
> @@ -140,8 +141,8 @@ void media_entity_graph_walk_start(struct
> media_entity_graph *graph, struct media_entity *entity);
> struct media_entity *
> media_entity_graph_walk_next(struct media_entity_graph *graph);
> -void media_entity_pipeline_start(struct media_entity *entity,
> - struct media_pipeline *pipe);
> +__must_check int media_entity_pipeline_start(struct media_entity *entity,
> + struct media_pipeline *pipe);
> void media_entity_pipeline_stop(struct media_entity *entity);
>
> #define media_entity_call(entity, operation, args...) \

--
Regards,

Laurent Pinchart