Re: [PATCH 1/2] media: media-entity.h: Add iterator for entity data links

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

Hi Daniel,

Thank you for the patch.

On Tue, Jun 21, 2022 at 05:34:56PM +0100, Daniel Scally wrote:
> Iterating over the links for an entity is a somewhat common need
> through the media subsystem, but generally the assumption is that
> they will all be data links. To meet that assumption add a new macro
> that iterates through an entity's links and skips non-data links.
> 
> Signed-off-by: Daniel Scally <djrscally@gmail.com>
> ---
>  include/media/media-entity.h | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/include/media/media-entity.h b/include/media/media-entity.h
> index a9a1c0ec5d1c..b13f67f33508 100644
> --- a/include/media/media-entity.h
> +++ b/include/media/media-entity.h
> @@ -550,6 +550,32 @@ static inline bool media_entity_enum_intersects(
>  				 min(ent_enum1->idx_max, ent_enum2->idx_max));
>  }
>  
> +static inline struct media_link *
> +__media_entity_next_data_link(struct media_entity *entity,
> +			      struct media_link *pos)

We could make this more dynamic by passing the link type as an argument,
adding more iteration macros for different link types in the future
would then be easier. Up to you.

> +{
> +	if (!pos) {
> +		list_for_each_entry(pos, &entity->links, list)
> +			if ((pos->flags & MEDIA_LNK_FL_LINK_TYPE) ==
> +			    MEDIA_LNK_FL_DATA_LINK)
> +				return pos;
> +
> +		return NULL;
> +	}
> +
> +	list_for_each_entry_continue(pos, &entity->links, list)
> +		if ((pos->flags & MEDIA_LNK_FL_LINK_TYPE) ==
> +		    MEDIA_LNK_FL_DATA_LINK)
> +			return pos;

This could be simplified to

	if (!pos)
		pos = list_entry(&entity->links, struct media_link, list);

	list_for_each_entry_continue(pos, &entity->links, list) {
		if ((pos->flags & MEDIA_LNK_FL_LINK_TYPE) ==
		    MEDIA_LNK_FL_DATA_LINK)
			return pos;
	}

> +
> +	return NULL;
> +}

This is a bit big for an inline function, could we move the
implementation to the .c file ?

> +
> +#define for_each_media_entity_data_link(entity, pos)		\

s/pos/link/ ?

> +	for (pos = __media_entity_next_data_link(entity, NULL);	\
> +	     pos;						\
> +	     pos = __media_entity_next_data_link(entity, pos))
> +

I'm afraid this needs documentation :-)
(https://lore.kernel.org/linux-media/20220301161156.1119557-13-tomi.valkeinen@ideasonboard.com/
can be used as an example)

>  /**
>   * gobj_to_entity - returns the struct &media_entity pointer from the
>   *	@gobj contained on it.

-- 
Regards,

Laurent Pinchart