Re: [PATCH 4/8] media: v4l2-subdev: Refactor warnings in v4l2_subdev_link_validate()

[Sakari Ailus <sakari.ailus@iki.fi>]

Hi Laurent,

Thanks for the patch.

On Wed, Jun 19, 2024 at 04:23:52AM +0300, Laurent Pinchart wrote:
> The v4l2_subdev_link_validate() function prints a one-time warning if it
> gets called on a link whose source or sink is not a subdev. As links get
> validated in the context of their sink, a call to the helper when the
> link's sink is not a subdev indicates that the driver has set its
> .link_validate() handler to v4l2_subdev_link_validate() on a non-subdev
> entity, which is a clear driver bug. On the other hand, the link's
> source not being a subdev indicates that the helper is used for a subdev
> connected to a video output device, which is a lesser issue, if only
> because this is currently common practice.
> 
> There are no drivers left in the kernel that use
> v4l2_subdev_link_validate() in a context where it may get called on a
> non-subdev sink. Replace the pr_warn_once() with a WARN_ON() in this
> case to make sure that new offenders won't be introduced.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> ---
>  drivers/media/v4l2-core/v4l2-subdev.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> index 4f71199bf592..2d5e39c79620 100644
> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> @@ -1451,11 +1451,15 @@ int v4l2_subdev_link_validate(struct media_link *link)
>  	bool states_locked;
>  	int ret;
>  
> -	if (!is_media_entity_v4l2_subdev(link->sink->entity) ||
> -	    !is_media_entity_v4l2_subdev(link->source->entity)) {
> -		pr_warn_once("%s of link '%s':%u->'%s':%u is not a V4L2 sub-device, driver bug!\n",
> -			     !is_media_entity_v4l2_subdev(link->sink->entity) ?
> -			     "sink" : "source",
> +	/*
> +	 * Links are validated in the context of the sink entity. Usage of this
> +	 * helper on a sink that is not a subdev is a clear driver bug.
> +	 */
> +	if (WARN_ON(!is_media_entity_v4l2_subdev(link->sink->entity)))
> +		return -EINVAL;

WARN*() is nowadays deprecated. Could you continue to use pr_warn_once()
for this (or dev_warn_one())?

> +
> +	if (!is_media_entity_v4l2_subdev(link->source->entity)) {
> +		pr_warn_once("source of link '%s':%u->'%s':%u is not a V4L2 sub-device, driver bug!\n",
>  			     link->source->entity->name, link->source->index,
>  			     link->sink->entity->name, link->sink->index);
>  		return 0;

-- 
Kind regards,

Sakari Ailus