[38/55] media: mc-entity: Add a new helper function to get a remote pad for a pad

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

The newly added media_entity_remote_source_pad() helper function handles
use cases where the entity has a link enabled uniqueness constraint
covering all pads. There are use cases where the constraint covers a
specific pad only. Add a new media_pad_remote_pad() function to handle
this. It operates as media_entity_remote_source_pad(), but on a given
pad instead of on the entity.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
---
 Documentation/driver-api/media/mc-core.rst |  4 +--
 drivers/media/mc/mc-entity.c               | 31 ++++++++++++++++++++++
 include/media/media-entity.h               | 18 +++++++++++++
 3 files changed, 51 insertions(+), 2 deletions(-)

+ Sakari and Hans

On Wed, Jun 15, 2022 at 04:11:10AM +0900, Paul Elder wrote:
> From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> 
> The newly added media_entity_remote_source_pad() helper function handles
> use cases where the entity has a link enabled uniqueness constraint
> covering all pads. There are use cases where the constraint covers a
> specific pad only. Add a new media_pad_remote_pad() function to handle
> this. It operates as media_entity_remote_source_pad(), but on a given
> pad instead of on the entity.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> ---
>  Documentation/driver-api/media/mc-core.rst |  4 +--
>  drivers/media/mc/mc-entity.c               | 31 ++++++++++++++++++++++
>  include/media/media-entity.h               | 18 +++++++++++++
>  3 files changed, 51 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/driver-api/media/mc-core.rst b/Documentation/driver-api/media/mc-core.rst
> index a2d1e32e3abb..83c3bdbf67be 100644
> --- a/Documentation/driver-api/media/mc-core.rst
> +++ b/Documentation/driver-api/media/mc-core.rst
> @@ -186,8 +186,8 @@ is required and the graph structure can be freed normally.
>  
>  Helper functions can be used to find a link between two given pads, or a pad
>  connected to another pad through an enabled link
> -(:c:func:`media_entity_find_link()`, :c:func:`media_entity_remote_pad()` and
> -:c:func:`media_entity_remote_source_pad()`).
> +(:c:func:`media_entity_find_link()`, :c:func:`media_entity_remote_pad()`,
> +:c:func:`media_entity_remote_source_pad()` and :c:func:`media_pad_remote_pad()`).
>  
>  Use count and power handling
>  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> diff --git a/drivers/media/mc/mc-entity.c b/drivers/media/mc/mc-entity.c
> index 1febf5a86be6..6429b0510bfb 100644
> --- a/drivers/media/mc/mc-entity.c
> +++ b/drivers/media/mc/mc-entity.c
> @@ -958,6 +958,37 @@ media_entity_remote_pad_unique(const struct media_entity *entity,
>  }
>  EXPORT_SYMBOL_GPL(media_entity_remote_pad_unique);
>  
> +struct media_pad *media_pad_remote_pad(const struct media_pad *pad)
> +{
> +	struct media_pad *found_pad = NULL;
> +	struct media_link *link;
> +
> +	list_for_each_entry(link, &pad->entity->links, list) {
> +		struct media_pad *remote_pad;
> +
> +		if (!(link->flags & MEDIA_LNK_FL_ENABLED))
> +			continue;
> +
> +		if (link->sink == pad)
> +			remote_pad = link->source;
> +		else if (link->source == pad)
> +			remote_pad = link->sink;
> +		else
> +			continue;
> +
> +		if (found_pad)
> +			return ERR_PTR(-ENOTUNIQ);
> +
> +		found_pad = remote_pad;
> +	}
> +
> +	if (!found_pad)
> +		return ERR_PTR(-ENOLINK);
> +
> +	return found_pad;
> +}
> +EXPORT_SYMBOL_GPL(media_pad_remote_pad);
> +
>  static void media_interface_init(struct media_device *mdev,
>  				 struct media_interface *intf,
>  				 u32 gobj_type,
> diff --git a/include/media/media-entity.h b/include/media/media-entity.h
> index 33d5f52719a0..bfe6a7b10a68 100644
> --- a/include/media/media-entity.h
> +++ b/include/media/media-entity.h
> @@ -904,6 +904,24 @@ media_entity_remote_source_pad(const struct media_entity *entity)
>  	return media_entity_remote_pad_unique(entity, MEDIA_PAD_FL_SOURCE);
>  }
>  
> +/**
> + * media_pad_remote_pad - Find a remote pad connected to a pad
> + * @pad: The pad
> + *
> + * Search for and return a remote pad connected to @pad through an enabled
> + * link. If multiple (or no) remote pads are found, an error is returned.
> + *
> + * The uniqueness constraint makes this helper function suitable for entities
> + * that support a single active source at a time on a given pad.
> + *
> + * Return: A pointer to the remote pad, or one of the following error pointers
> + * if an error occurs:
> + *
> + * * -ENOTUNIQ - Multiple links are enabled
> + * * -ENOLINK - No connected pad found
> + */
> +struct media_pad *media_pad_remote_pad(const struct media_pad *pad);
> +
>  /**
>   * media_entity_is_streaming - Test if an entity is part of a streaming pipeline
>   * @entity: The entity
> -- 
> 2.30.2
>