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

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

Hi Tomi,

On Mon, Aug 26, 2024 at 02:43:47PM +0300, Tomi Valkeinen wrote:
> 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?

Correct. The VSP has both capture and output video devices, and this
helper function is used for both.

> 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?

Because it validates a link. Which of the sink or source entity would
you pass to the function ?

> > +
> > +	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? =)

Because you haven't sent patches yet ;-)

But jokes aside, because there's no 1:1 mapping between media bus codes
and pixel formats, so drivers have to validate at least that part.

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

-- 
Regards,

Laurent Pinchart