linux-kernel - Re: [PATCH v3 7/8] media: uvcvideo: Set a different name for the metadata entity

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Date:   Sat, 13 Mar 2021 00:27:53 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Tomasz Figa <tfiga@...omium.org>, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, senozhatsky@...omium.org,
        Hans Verkuil <hverkuil@...all.nl>
Subject: Re: [PATCH v3 7/8] media: uvcvideo: Set a different name for the
 metadata entity

Hi Ricardo,

Thank you for the patch.

On Fri, Mar 12, 2021 at 01:48:29PM +0100, Ricardo Ribalda wrote:
> All the entities must have a unique name. And now that we are at it, we
> append the entity->id to the name to avoid collisions on multi-chain
> devices.
> 
> Fixes v4l2-compliance:
> Media Controller ioctls:
>                 fail: v4l2-test-media.cpp(205): v2_entity_names_set.find(key) != v2_entity_names_set.end()
>         test MEDIA_IOC_G_TOPOLOGY: FAIL
>                 fail: v4l2-test-media.cpp(394): num_data_links != num_links
> 	test MEDIA_IOC_ENUM_ENTITIES/LINKS: FAIL
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/usb/uvc/uvc_driver.c | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index 35873cf2773d..6c928e708615 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -2154,6 +2154,18 @@ static void uvc_unregister_video(struct uvc_device *dev)
>  #endif
>  }
>  
> +static int uvc_oterm_id(struct uvc_video_chain *chain)
> +{
> +	struct uvc_entity *entity;
> +
> +	list_for_each_entry(entity, &chain->entities, chain) {
> +		if (UVC_ENTITY_IS_OTERM(entity))
> +			return entity->id;

It can also be an ITERM for output devices. You can drop this function
and use stream>header.bTerminalLink below (see uvc_stream_by_id() and
its usage in uvc_register_terms()).

> +	}
> +
> +	return -1;
> +}
> +
>  int uvc_register_video_device(struct uvc_device *dev,
>  			      struct uvc_streaming *stream,
>  			      struct video_device *vdev,
> @@ -2162,6 +2174,8 @@ int uvc_register_video_device(struct uvc_device *dev,
>  			      const struct v4l2_file_operations *fops,
>  			      const struct v4l2_ioctl_ops *ioctl_ops)
>  {
> +	char prefix[sizeof(vdev->name) - 9];
> +	const char *suffix;
>  	int ret;
>  
>  	/* Initialize the video buffers queue. */
> @@ -2190,16 +2204,21 @@ int uvc_register_video_device(struct uvc_device *dev,
>  	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
>  	default:
>  		vdev->device_caps = V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_STREAMING;
> +		suffix = "video";
>  		break;
>  	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
>  		vdev->device_caps = V4L2_CAP_VIDEO_OUTPUT | V4L2_CAP_STREAMING;
> +		suffix = "out";

I wonder if these two should be video-cap and video-out (or vid-cap and
vid-out if you want to shorten them) ?

>  		break;
>  	case V4L2_BUF_TYPE_META_CAPTURE:
>  		vdev->device_caps = V4L2_CAP_META_CAPTURE | V4L2_CAP_STREAMING;
> +		suffix = "meta";
>  		break;
>  	}
>  
> -	strscpy(vdev->name, dev->name, sizeof(vdev->name));
> +	strscpy(prefix, dev->name, sizeof(prefix));
> +	snprintf(vdev->name, sizeof(vdev->name), "%s-%d %s", prefix,

The unit ID is never negative, so %u ?

> +		 uvc_oterm_id(stream->chain), suffix);

Truncating the device name at the beginning of the video node name isn't
very nice :-S How about the following ?

	snprintf(vdev->name, sizeof(vdev->name), "%s-%u (%s)", type_name,
		 uvc_oterm_id(stream->chain), dev->name);

with the suffix variable renamed to type_name ?

Thinking some more about it, vdev->name serves two purposes in the
driver: creating the entity name, and reporting the card name in
querycap. The former is done in the V4L2 core, which uses vdev->name
as-is. In this context, we con't need to add dev->name, it would be
redundant as the media controller device already reports it. The latter
is done in uvc_ioctl_querycap(). How about dropping dev->name from
vdev->name, and modifying uvc_ioctl_querycap() to use dev->name instead
of cap->card ?

>  
>  	/*
>  	 * Set the driver data before calling video_register_device, otherwise

-- 
Regards,

Laurent Pinchart