Re: [PATCH v2 7/7] [DNI] media: renesas: vsp1: Validate all links through .link_validate()

[Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>]

Hi,

On 22/08/2024 18:45, Laurent Pinchart wrote:
> Move validation of the links between video devices and subdevs,
> performed manually in vsp1_video_streamon(), to the video device
> .link_validate() handler.
> 
> This is how drivers should be implemented, but sadly, doing so for the
> vsp1 driver could break userspace, introducing a regression. This patch
> serves as an example to showcase usage of the .link_validate()
> operation, but should not be merged.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> ---
>   .../media/platform/renesas/vsp1/vsp1_video.c  | 98 +++++++------------
>   1 file changed, 37 insertions(+), 61 deletions(-)
> 
> diff --git a/drivers/media/platform/renesas/vsp1/vsp1_video.c b/drivers/media/platform/renesas/vsp1/vsp1_video.c
> index e728f9f5160e..14575698bbe7 100644
> --- a/drivers/media/platform/renesas/vsp1/vsp1_video.c
> +++ b/drivers/media/platform/renesas/vsp1/vsp1_video.c
> @@ -45,51 +45,6 @@
>    * Helper functions
>    */
>   
> -static struct v4l2_subdev *
> -vsp1_video_remote_subdev(struct media_pad *local, u32 *pad)
> -{
> -	struct media_pad *remote;
> -
> -	remote = media_pad_remote_pad_first(local);
> -	if (!remote || !is_media_entity_v4l2_subdev(remote->entity))
> -		return NULL;
> -
> -	if (pad)
> -		*pad = remote->index;
> -
> -	return media_entity_to_v4l2_subdev(remote->entity);
> -}
> -
> -static int vsp1_video_verify_format(struct vsp1_video *video)
> -{
> -	struct v4l2_subdev_format fmt = {
> -		.which = V4L2_SUBDEV_FORMAT_ACTIVE,
> -	};
> -	struct v4l2_subdev *subdev;
> -	int ret;
> -
> -	subdev = vsp1_video_remote_subdev(&video->pad, &fmt.pad);
> -	if (subdev == NULL)
> -		return -EINVAL;
> -
> -	ret = v4l2_subdev_call(subdev, pad, get_fmt, NULL, &fmt);
> -	if (ret < 0)
> -		return ret == -ENOIOCTLCMD ? -EINVAL : ret;
> -
> -	if (video->rwpf->fmtinfo->mbus != fmt.format.code ||
> -	    video->rwpf->format.height != fmt.format.height ||
> -	    video->rwpf->format.width != fmt.format.width) {
> -		dev_dbg(video->vsp1->dev,
> -			"Format mismatch: 0x%04x/%ux%u != 0x%04x/%ux%u\n",
> -			video->rwpf->fmtinfo->mbus, video->rwpf->format.width,
> -			video->rwpf->format.height, fmt.format.code,
> -			fmt.format.width, fmt.format.height);
> -		return -EPIPE;
> -	}
> -
> -	return 0;
> -}
> -
>   static int __vsp1_video_try_format(struct vsp1_video *video,
>   				   struct v4l2_pix_format_mplane *pix,
>   				   const struct vsp1_format_info **fmtinfo)
> @@ -991,14 +946,6 @@ vsp1_video_streamon(struct file *file, void *fh, enum v4l2_buf_type type)
>   
>   	mutex_unlock(&mdev->graph_mutex);
>   
> -	/*
> -	 * Verify that the configured format matches the output of the connected
> -	 * subdev.
> -	 */
> -	ret = vsp1_video_verify_format(video);
> -	if (ret < 0)
> -		goto err_stop;
> -
>   	/* Start the queue. */
>   	ret = vb2_streamon(&video->queue, type);
>   	if (ret < 0)
> @@ -1087,14 +1034,43 @@ static const struct v4l2_file_operations vsp1_video_fops = {
>   
>   static int vsp1_video_link_validate(struct media_link *link)
>   {
> -	/*
> -	 * Ideally, link validation should be implemented here instead of
> -	 * calling vsp1_video_verify_format() in vsp1_video_streamon()
> -	 * manually. That would however break userspace that start one video
> -	 * device before configures formats on other video devices in the
> -	 * pipeline. This operation is just a no-op to silence the warnings
> -	 * from v4l2_subdev_link_validate().
> -	 */
> +	struct v4l2_subdev_format fmt = {
> +		.which = V4L2_SUBDEV_FORMAT_ACTIVE,
> +	};
> +	struct v4l2_subdev *subdev;
> +	struct media_entity *entity;
> +	struct media_pad *remote;
> +	struct vsp1_video *video;
> +	int ret;
> +
> +	if (is_media_entity_v4l2_video_device(link->source->entity)) {
> +		entity = link->source->entity;
> +		remote = link->sink;
> +	} else {
> +		entity = link->sink->entity;
> +		remote = link->source;
> +	}

This looks a bit odd. So this device can be either a source and a sink?

This made me also wonder about the .link_validate(). It's the only 
media_entity_operations op that does not get the media_entity as a 
parameter. Which here means the driver has to go and "guess" whether it 
is the source or the sink of the given link.

I wonder if there's a reason why .link_validate() doesn't have the 
media_entity parameter?

> +
> +	fmt.pad = remote->index;
> +
> +	subdev = media_entity_to_v4l2_subdev(remote->entity);
> +	ret = v4l2_subdev_call(subdev, pad, get_fmt, NULL, &fmt);
> +	if (ret < 0)
> +		return ret == -ENOIOCTLCMD ? -EINVAL : ret;
> +
> +	video = to_vsp1_video(media_entity_to_video_device(entity));
> +
> +	if (video->rwpf->fmtinfo->mbus != fmt.format.code ||
> +	    video->rwpf->format.height != fmt.format.height ||
> +	    video->rwpf->format.width != fmt.format.width) {
> +		dev_dbg(video->vsp1->dev,
> +			"Format mismatch: 0x%04x/%ux%u != 0x%04x/%ux%u\n",
> +			video->rwpf->fmtinfo->mbus, video->rwpf->format.width,
> +			video->rwpf->format.height, fmt.format.code,
> +			fmt.format.width, fmt.format.height);
> +		return -EPIPE;
> +	}

Why don't we have a common videodev state which could be used to do 
these validations in a common function? =)

Fwiw:
Reviewed-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>

  Tomi