Re: [RFC 2/4] media: Check for active links on pads with MEDIA_PAD_FL_MUST_CONNECT flag

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Sakari,

Thank you for the patch.

On Friday 19 July 2013 20:55:07 Sakari Ailus wrote:
> Do not allow streaming if a pad with MEDIA_PAD_FL_MUST_CONNECT flag is not
> connected by an active link.
> 
> This patch makes it possible to avoid drivers having to check for the most
> common case of link state validation: a sink pad that must be connected.
> 
> Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
> ---
>  drivers/media/media-entity.c |   34 +++++++++++++++++++++++++++-------
>  1 file changed, 27 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/media/media-entity.c b/drivers/media/media-entity.c
> index cb30ffb..4e58f8a 100644
> --- a/drivers/media/media-entity.c
> +++ b/drivers/media/media-entity.c
> @@ -20,6 +20,7 @@
>   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 
> USA */
> 
> +#include <linux/bitmap.h>
>  #include <linux/module.h>
>  #include <linux/slab.h>
>  #include <media/media-entity.h>
> @@ -227,6 +228,7 @@ __must_check int media_entity_pipeline_start(struct
> media_entity *entity, media_entity_graph_walk_start(&graph, entity);
> 
>  	while ((entity = media_entity_graph_walk_next(&graph))) {
> +		DECLARE_BITMAP(active, entity->num_pads);
>  		unsigned int i;
> 
>  		entity->stream_count++;
> @@ -240,21 +242,39 @@ __must_check int media_entity_pipeline_start(struct
> media_entity *entity, if (!entity->ops || !entity->ops->link_validate)
>  			continue;
> 
> +		bitmap_zero(active, entity->num_pads);
> +
>  		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))
> -				continue;
> -
> -			/* Are we the sink or not? */
> -			if (link->sink->entity != entity)
> +			struct media_pad *pad = link->sink->entity == entity
> +				? link->sink : link->source;
> +
> +			/*
> +			 * Pads that either do not need to connect or
> +			 * are connected through an enabled link are
> +			 * fine.
> +			 */
> +			if (!(pad->flags & MEDIA_PAD_FL_MUST_CONNECT)
> +			    || link->flags & MEDIA_LNK_FL_ENABLED)
> +				bitmap_set(active, pad->index, 1);
> +
> +			/*
> +			 * Link validation will only take place for
> +			 * sink ends of the link that are enabled.
> +			 */
> +			if (link->sink != pad
> +			    || !(link->flags & MEDIA_LNK_FL_ENABLED))
>  				continue;
> 
>  			ret = entity->ops->link_validate(link);
>  			if (ret < 0 && ret != -ENOIOCTLCMD)
>  				goto error;
>  		}
> +
> +		if (!bitmap_full(active, entity->num_pads)) {
> +			ret = -EPIPE;
> +			goto error;
> +		}

I'm afraid that won't work if one of the pads has no links. In that case the 
bitmap won't be full. I think you will have to iterate separately on the links 
to validate them, and on the pads to check the flags.

>  	}
> 
>  	mutex_unlock(&mdev->graph_mutex);
-- 
Regards,

Laurent Pinchart