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

Laurent Pinchart
2026-04-16T16:29:25Z

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