Re: [PATCH v4 22/29] media: mc: Add MEDIA_LNK_FL_VALIDATE_LATE

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

On Wed, Apr 08, 2026 at 06:39:31PM +0300, Sakari Ailus wrote:
> Add MEDIA_LNK_FL_VALIDATE_LATE flag to support late validation of links.
> This is serving the use case where video devices are configured and
> started streaming indepenently of each other but this sequence may be run
> in series, in such a way that a video device in a pipeline starts
> streaming before another one is configured.
> 
> Before this flag, drivers have resorted to implementing the link
> validation separately for the video nodes as part of streaming start
> sequence.
> 
> media_pipeline_start() shall be called on each leaf entity connected to
> the graph with a link where MEDIA_LNK_FL_VALIDATE_LATE is set before
> uphardware operation.

I don't like this much, especially given that there are no users in this
series, so I can't check how it's used. Let's postpone it.

> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
>  .../media/mediactl/media-ioc-setup-link.rst   |  4 +
>  .../media/mediactl/media-types.rst            |  5 ++
>  drivers/media/mc/mc-entity.c                  | 82 ++++++++++++++++++-
>  include/uapi/linux/media.h                    |  1 +
>  4 files changed, 88 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/userspace-api/media/mediactl/media-ioc-setup-link.rst b/Documentation/userspace-api/media/mediactl/media-ioc-setup-link.rst
> index 23208300cb61..7c2bced57e77 100644
> --- a/Documentation/userspace-api/media/mediactl/media-ioc-setup-link.rst
> +++ b/Documentation/userspace-api/media/mediactl/media-ioc-setup-link.rst
> @@ -49,6 +49,10 @@ Only links marked with the ``DYNAMIC`` link flag can be enabled/disabled
>  while streaming media data. Attempting to enable or disable a streaming
>  non-dynamic link will return an ``EBUSY`` error code.
>  
> +Pipeline validation may be delayed for links marked with the ``VALIDATE_LATE``
> +flag until actual hardware operation even if the rest of the pipeline would be
> +validated at an earlier point of time.
> +
>  If the specified link can't be found the driver returns with an ``EINVAL``
>  error code.
>  
> diff --git a/Documentation/userspace-api/media/mediactl/media-types.rst b/Documentation/userspace-api/media/mediactl/media-types.rst
> index 6332e8395263..d6a690655a01 100644
> --- a/Documentation/userspace-api/media/mediactl/media-types.rst
> +++ b/Documentation/userspace-api/media/mediactl/media-types.rst
> @@ -391,6 +391,7 @@ must be set for every pad.
>  .. _MEDIA-LNK-FL-ENABLED:
>  .. _MEDIA-LNK-FL-IMMUTABLE:
>  .. _MEDIA-LNK-FL-DYNAMIC:
> +.. _MEDIA-LNK-FL-VALIDATE-LATE:
>  .. _MEDIA-LNK-FL-LINK-TYPE:
>  
>  .. flat-table:: Media link flags
> @@ -410,6 +411,10 @@ must be set for every pad.
>         -  The link enabled state can be modified during streaming. This flag
>  	  is set by drivers and is read-only for applications.
>  
> +    *  -  ``MEDIA_LNK_FL_VALIDATE_LATE``
> +       -  The validation of the link may be delayed up to until the start of
> +	  hardware operation.
> +
>      *  -  ``MEDIA_LNK_FL_LINK_TYPE``
>         -  This is a bitmask that defines the type of the link. The following
>  	  link types are currently supported:
> diff --git a/drivers/media/mc/mc-entity.c b/drivers/media/mc/mc-entity.c
> index 287eded356bb..5b0162f81425 100644
> --- a/drivers/media/mc/mc-entity.c
> +++ b/drivers/media/mc/mc-entity.c
> @@ -771,7 +771,7 @@ static int media_pipeline_populate(struct media_pipeline *pipe,
>  static int
>  __media_pipeline_validate_one(struct media_pad *origin,
>  			      struct media_pad *pad, struct media_link *link,
> -			      bool *has_enabled_link)
> +			      bool *has_enabled_link, bool skip_validation)
>  {
>  	struct media_device *mdev = origin->graph_obj.mdev;
>  	struct media_entity *entity = pad->entity;
> @@ -784,6 +784,9 @@ __media_pipeline_validate_one(struct media_pad *origin,
>  	if (has_enabled_link)
>  		*has_enabled_link = true;
>  
> +	if (skip_validation)
> +		return 0;
> +
>  	/* Skip validation if the current pad isn't the sink pad of the link. */
>  	if (link->sink != pad)
>  		return 0;
> @@ -825,11 +828,48 @@ __must_check int __media_pipeline_start(struct media_pad *origin,
>  		return -EINVAL;
>  
>  	/*
> -	 * If the pipeline has already been started, it is guaranteed to be
> -	 * valid, so just increase the start count.
> +	 * Increase start count on pipelines that have been validated
> +	 * earlier. Also check links with the VALIDATE_LATE flag here.
>  	 */
>  	if (pipe->start_count) {
> +		struct media_link *link;
> +
> +		link = __media_entity_next_link(origin->entity, NULL,
> +						MEDIA_LNK_FL_DATA_LINK);
> +		if (link && link->flags & MEDIA_LNK_FL_VALIDATE_LATE) {
> +			struct media_link *link2 =
> +				__media_entity_next_link(origin->entity, link,
> +							 MEDIA_LNK_FL_DATA_LINK);
> +			bool has_enabled_link = false;
> +
> +			/*
> +			 * Only a single pad is allowed for VALIDATE_LATE
> +			 * links. That pad needs to have exactly one link.
> +			 */
> +			if (origin->entity->num_pads != 1)
> +				return -EINVAL;
> +
> +			if (!link || link2)
> +				return -EINVAL;
> +
> +			dev_dbg(mdev->dev,
> +				"Validating pad '%s':%u late\n",
> +				origin->entity->name, origin->index);
> +
> +			ret = __media_pipeline_validate_one(link->sink,
> +							    link->sink, link,
> +							    &has_enabled_link,
> +							    false);
> +			if (ret)
> +				return ret;
> +
> +			if (origin->flags & MEDIA_PAD_FL_MUST_CONNECT &&
> +			    !has_enabled_link)
> +				return -ENOLINK;
> +		}
> +
>  		pipe->start_count++;
> +
>  		return 0;
>  	}
>  
> @@ -873,12 +913,19 @@ __must_check int __media_pipeline_start(struct media_pad *origin,
>  		 * the connected sink pad to avoid duplicating checks.
>  		 */
>  		for_each_media_entity_data_link(entity, link) {
> +			/* Skip late-validated links not connected to origin. */
> +			bool skip_validation =
> +				link->flags & MEDIA_LNK_FL_VALIDATE_LATE &&
> +				link->sink != origin &&
> +				link->source != origin;
> +
>  			/* Skip links unrelated to the current pad. */
>  			if (link->sink != pad && link->source != pad)
>  				continue;
>  
>  			ret = __media_pipeline_validate_one(origin, pad, link,
> -							    &has_enabled_link);
> +							    &has_enabled_link,
> +							    skip_validation);
>  			if (ret)
>  				goto error;
>  		}
> @@ -1158,6 +1205,33 @@ media_create_pad_link(struct media_entity *source, u16 source_pad,
>  	if (WARN_ON(!(sink->pads[sink_pad].flags & MEDIA_PAD_FL_SINK)))
>  		return -EINVAL;
>  
> +	/*
> +	 * With the late validate flag, either source or sink shall have exactly
> +	 * one pad and no links before this one. Similarly, no links may be
> +	 * added to entities with a single pad and an existing late-validated
> +	 * link.
> +	 */
> +	if (flags & MEDIA_LNK_FL_VALIDATE_LATE) {
> +		if (!(source->num_pads == 1 && !source->num_links) &&
> +		    !(sink->num_pads == 1 && !sink->num_links))
> +			return -EINVAL;
> +	} else {
> +		struct media_entity *entities[] = { source, sink };
> +
> +		for (unsigned int i = 0; i < ARRAY_SIZE(entities); i++) {
> +			if (entities[i]->num_pads != 1)
> +				continue;
> +
> +			struct media_link *__link =
> +				__media_entity_next_link(entities[i], NULL,
> +							 MEDIA_LNK_FL_DATA_LINK);
> +
> +			if (__link &&
> +			    __link->flags & MEDIA_LNK_FL_VALIDATE_LATE)
> +				return -EINVAL;
> +		}
> +	}
> +
>  	link = media_add_link(&source->links);
>  	if (link == NULL)
>  		return -ENOMEM;
> diff --git a/include/uapi/linux/media.h b/include/uapi/linux/media.h
> index 1c80b1d6bbaf..c96e2118ea99 100644
> --- a/include/uapi/linux/media.h
> +++ b/include/uapi/linux/media.h
> @@ -219,6 +219,7 @@ struct media_pad_desc {
>  #define MEDIA_LNK_FL_ENABLED			(1U << 0)
>  #define MEDIA_LNK_FL_IMMUTABLE			(1U << 1)
>  #define MEDIA_LNK_FL_DYNAMIC			(1U << 2)
> +#define MEDIA_LNK_FL_VALIDATE_LATE		(1U << 3)
>  
>  #define MEDIA_LNK_FL_LINK_TYPE			(0xf << 28)
>  #  define MEDIA_LNK_FL_DATA_LINK		(0U << 28)

-- 
Regards,

Laurent Pinchart