LinuxTV Patchwork [v2,3/3] uvcvideo: add a metadata device node

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Submitter Guennadi Liakhovetski
Date Dec. 2, 2016, 10:53 a.m.
Message ID <Pine.LNX.4.64.1612021141110.11357@axis700.grange>
Download mbox | patch
Permalink /patch/38415/
State New
Delegated to: Laurent Pinchart
Headers show

Comments

Guennadi Liakhovetski - Dec. 2, 2016, 10:53 a.m.
Some UVC video cameras contain metadata in their payload headers. This
patch extracts that data, skipping the standard part of the header, on
both bulk and isochronous endpoints and makes it available to the user
space on a separate video node, using the V4L2_CAP_META_CAPTURE
capability and the V4L2_BUF_TYPE_META_CAPTURE buffer queue type. Even
though different cameras will have different metadata formats, we use
the same V4L2_META_FMT_UVC pixel format for all of them. Users have to
parse data, based on the specific camera model information.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@intel.com>
---

v2:
- updated to the current media/master
- removed superfluous META capability from capture nodes
- now the complete UVC payload header is copied to buffers, including 
  standard fields

Still open for discussion: is this really OK to always create an 
additional metadata node for each UVC camera or UVC video interface.

IIUC, Laurent's metadata node patch 
https://patchwork.linuxtv.org/patch/36810/ has been acked by Hans and the 
only thing, that's preventing it from being merged it the lack of 
documentation. While waiting for documentation, I'd appreciate some 
discussion of this patch to beat it into shape soon enough and have it 
ready for merge soon after Laurent's patches are pulled in.

Thanks
Guennadi

 drivers/media/usb/uvc/Makefile       |   2 +-
 drivers/media/usb/uvc/uvc_driver.c   |  10 ++
 drivers/media/usb/uvc/uvc_isight.c   |   2 +-
 drivers/media/usb/uvc/uvc_metadata.c | 228 +++++++++++++++++++++++++++++++++++
 drivers/media/usb/uvc/uvc_video.c    |  47 ++++++--
 drivers/media/usb/uvc/uvcvideo.h     |  12 +-
 drivers/media/v4l2-core/v4l2-ioctl.c |   1 +
 include/uapi/linux/uvcvideo.h        |  10 ++
 include/uapi/linux/videodev2.h       |   3 +
 9 files changed, 304 insertions(+), 11 deletions(-)
 create mode 100644 drivers/media/usb/uvc/uvc_metadata.c
Laurent Pinchart - Dec. 5, 2016, 10:53 a.m.
Hi Guennadi,

Thank you for the patch.

On Friday 02 Dec 2016 11:53:23 Guennadi Liakhovetski wrote:
> Some UVC video cameras contain metadata in their payload headers. This
> patch extracts that data, skipping the standard part of the header, on
> both bulk and isochronous endpoints and makes it available to the user
> space on a separate video node, using the V4L2_CAP_META_CAPTURE
> capability and the V4L2_BUF_TYPE_META_CAPTURE buffer queue type. Even
> though different cameras will have different metadata formats, we use
> the same V4L2_META_FMT_UVC pixel format for all of them. Users have to
> parse data, based on the specific camera model information.
> 
> Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@intel.com>
> ---
> 
> v2:
> - updated to the current media/master
> - removed superfluous META capability from capture nodes
> - now the complete UVC payload header is copied to buffers, including
>   standard fields
> 
> Still open for discussion: is this really OK to always create an
> additional metadata node for each UVC camera or UVC video interface.
>
> IIUC, Laurent's metadata node patch
> https://patchwork.linuxtv.org/patch/36810/ has been acked by Hans and the
> only thing, that's preventing it from being merged it the lack of
> documentation. While waiting for documentation, I'd appreciate some
> discussion of this patch to beat it into shape soon enough and have it
> ready for merge soon after Laurent's patches are pulled in.
> 
> Thanks
> Guennadi
> 
>  drivers/media/usb/uvc/Makefile       |   2 +-
>  drivers/media/usb/uvc/uvc_driver.c   |  10 ++
>  drivers/media/usb/uvc/uvc_isight.c   |   2 +-
>  drivers/media/usb/uvc/uvc_metadata.c | 228 +++++++++++++++++++++++++++++++
>  drivers/media/usb/uvc/uvc_video.c    |  47 ++++++--
>  drivers/media/usb/uvc/uvcvideo.h     |  12 +-
>  drivers/media/v4l2-core/v4l2-ioctl.c |   1 +
>  include/uapi/linux/uvcvideo.h        |  10 ++
>  include/uapi/linux/videodev2.h       |   3 +
>  9 files changed, 304 insertions(+), 11 deletions(-)
>  create mode 100644 drivers/media/usb/uvc/uvc_metadata.c

[snip]

> diff --git a/drivers/media/usb/uvc/uvc_driver.c
> b/drivers/media/usb/uvc/uvc_driver.c index 04bf350..edb67ac 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -1866,6 +1866,9 @@ static void uvc_unregister_video(struct uvc_device
> *dev)
> 
>  		video_unregister_device(&stream->vdev);
> 
> +		if (video_is_registered(&stream->meta.vdev))
> +			video_unregister_device(&stream->meta.vdev);

video_unregister_device() contains a video_is_registered(), no need to 
duplicate it.

> +
>  		uvc_debugfs_cleanup_stream(stream);
>  	}
> 
> @@ -1926,6 +1929,13 @@ static int uvc_register_video(struct uvc_device *dev,
> return ret;
>  	}
> 
> +	/*
> +	 * Register a metadata node. TODO: shall this only be enabled for some
> +	 * cameras?
> +	 */
> +	if (!(dev->quirks & UVC_QUIRK_BUILTIN_ISIGHT))
> +		uvc_meta_register(stream);
> +

I think so, only for the cameras that can produce metadata.

>  	if (stream->type == V4L2_BUF_TYPE_VIDEO_CAPTURE)
>  		stream->chain->caps |= V4L2_CAP_VIDEO_CAPTURE;
>  	else

[snip]

> diff --git a/drivers/media/usb/uvc/uvc_metadata.c
> b/drivers/media/usb/uvc/uvc_metadata.c new file mode 100644
> index 0000000..ddf77d9
> --- /dev/null
> +++ b/drivers/media/usb/uvc/uvc_metadata.c
> @@ -0,0 +1,228 @@
> +/*
> + *      uvc_metadata.c  --  USB Video Class driver - Metadata handling
> + *
> + *      Copyright (C) 2016
> + *          Guennadi Liakhovetski (guennadi.liakhovetski@intel.com)
> + *
> + *      This program is free software; you can redistribute it and/or
> modify
> + *      it under the terms of the GNU General Public License as published
> by
> + *      the Free Software Foundation; either version 2 of the License, or
> + *      (at your option) any later version.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +#include <linux/usb.h>
> +#include <linux/videodev2.h>
> +
> +#include <media/v4l2-ioctl.h>
> +#include <media/videobuf2-v4l2.h>
> +#include <media/videobuf2-vmalloc.h>
> +
> +#include "uvcvideo.h"
> +
> +static inline struct uvc_buffer *to_uvc_buffer(struct vb2_v4l2_buffer
> *vbuf)
> +{
> +	return container_of(vbuf, struct uvc_buffer, buf);
> +}

You can move this function to uvcvideo.h and use it in uvc_queue.c (a separate 
patch would be best).

> +/* ------------------------------------------------------------------------
> + * videobuf2 Queue Operations
> + */
> +
> +static int meta_queue_setup(struct vb2_queue *vq, unsigned int *nbuffers,
> +			    unsigned int *nplanes, unsigned int sizes[],
> +			    struct device *alloc_devs[])
> +{
> +	if (*nplanes) {
> +		if (*nplanes != 1)
> +			return -EINVAL;
> +
> +		if (sizes[0] < UVC_PAYLOAD_HEADER_MAX_SIZE)
> +			return -EINVAL;
> +
> +		return 0;
> +	}
> +
> +	*nplanes = 1;
> +	sizes[0] = UVC_PAYLOAD_HEADER_MAX_SIZE;
> +
> +	return 0;
> +}
> +
> +static int meta_buffer_prepare(struct vb2_buffer *vb)
> +{
> +	struct vb2_v4l2_buffer *vbuf = to_vb2_v4l2_buffer(vb);
> +	struct uvc_buffer *buf = to_uvc_buffer(vbuf);
> +
> +	if (vb->num_planes != 1)
> +		return -EINVAL;
> +
> +	if (vb2_plane_size(vb, 0) < UVC_PAYLOAD_HEADER_MAX_SIZE)
> +		return -EINVAL;
> +
> +	buf->state = UVC_BUF_STATE_QUEUED;
> +	buf->error = 0;
> +	buf->mem = vb2_plane_vaddr(vb, 0);
> +	buf->length = vb2_plane_size(vb, 0);
> +	buf->bytesused = 0;
> +
> +	return 0;
> +}
> +
> +static void meta_buffer_queue(struct vb2_buffer *vb)
> +{
> +	struct vb2_v4l2_buffer *vbuf = to_vb2_v4l2_buffer(vb);
> +	struct uvc_video_queue *queue = vb2_get_drv_priv(vb->vb2_queue);
> +	struct uvc_buffer *buf = to_uvc_buffer(vbuf);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&queue->irqlock, flags);

Shouldn't you handle the UVC_QUEUE_DISCONNECTED flag here ?

> +	list_add_tail(&buf->queue, &queue->irqqueue);
> +	spin_unlock_irqrestore(&queue->irqlock, flags);
> +}
> +
> +static int meta_start_streaming(struct vb2_queue *vq, unsigned int count)
> +{
> +	return 0;
> +}
> +
> +static void meta_stop_streaming(struct vb2_queue *vq)
> +{
> +	struct uvc_video_queue *queue = vb2_get_drv_priv(vq);
> +	struct uvc_buffer *buffer;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&queue->irqlock, flags);
> +
> +	/* Remove all buffers from the IRQ queue. */
> +	list_for_each_entry(buffer, &queue->irqqueue, queue)
> +		vb2_buffer_done(&buffer->buf.vb2_buf, VB2_BUF_STATE_ERROR);
> +	INIT_LIST_HEAD(&queue->irqqueue);
> +
> +	spin_unlock_irqrestore(&queue->irqlock, flags);
> +}
> +
> +static struct vb2_ops uvc_meta_queue_ops = {
> +	.queue_setup = meta_queue_setup,
> +	.buf_prepare = meta_buffer_prepare,
> +	.buf_queue = meta_buffer_queue,
> +	.wait_prepare = vb2_ops_wait_prepare,
> +	.wait_finish = vb2_ops_wait_finish,
> +	.start_streaming = meta_start_streaming,
> +	.stop_streaming = meta_stop_streaming,
> +};

How about reusing the uvc_queue.c implementation, with a few new checks for 
metadata buffers where needed, instead of duplicating code ? At first sight 
the changes don't seem to be too intrusive (but I might have overlooked 
something).

> +/* ------------------------------------------------------------------------
> + * V4L2 ioctls
> + */
> +
> +static int meta_v4l2_querycap(struct file *file, void *fh,
> +			      struct v4l2_capability *cap)
> +{
> +	struct v4l2_fh *vfh = file->private_data;
> +	struct uvc_streaming *stream = video_get_drvdata(vfh->vdev);
> +
> +	cap->device_caps = V4L2_CAP_META_CAPTURE
> +			 | V4L2_CAP_STREAMING;
> +	cap->capabilities = V4L2_CAP_DEVICE_CAPS | cap->device_caps
> +			  | stream->chain->caps;

If you set the device_caps field of struct video_device you won't need the 
above four lines.

> +	strlcpy(cap->driver, "uvcvideo", sizeof(cap->driver));
> +	strlcpy(cap->card, vfh->vdev->name, sizeof(cap->card));
> +	usb_make_path(stream->dev->udev, cap->bus_info, sizeof(cap-
>bus_info));
> +
> +	return 0;
> +}
> +
> +static int meta_v4l2_get_format(struct file *file, void *fh,
> +				struct v4l2_format *format)
> +{
> +	struct v4l2_fh *vfh = file->private_data;
> +	struct v4l2_meta_format *fmt = &format->fmt.meta;
> +
> +	if (format->type != vfh->vdev->queue->type)
> +		return -EINVAL;
> +
> +	memset(fmt, 0, sizeof(*fmt));
> +
> +	fmt->dataformat = V4L2_META_FMT_UVC;
> +	fmt->buffersize = UVC_PAYLOAD_HEADER_MAX_SIZE;
> +
> +	return 0;
> +}
> +
> +static const struct v4l2_ioctl_ops uvc_meta_ioctl_ops = {
> +	.vidioc_querycap		= meta_v4l2_querycap,
> +	.vidioc_g_fmt_meta_cap		= meta_v4l2_get_format,
> +	.vidioc_s_fmt_meta_cap		= meta_v4l2_get_format,
> +	.vidioc_try_fmt_meta_cap	= meta_v4l2_get_format,
> +	.vidioc_reqbufs			= vb2_ioctl_reqbufs,
> +	.vidioc_querybuf		= vb2_ioctl_querybuf,
> +	.vidioc_qbuf			= vb2_ioctl_qbuf,
> +	.vidioc_dqbuf			= vb2_ioctl_dqbuf,
> +	.vidioc_create_bufs		= vb2_ioctl_create_bufs,
> +	.vidioc_prepare_buf		= vb2_ioctl_prepare_buf,
> +	.vidioc_streamon		= vb2_ioctl_streamon,
> +	.vidioc_streamoff		= vb2_ioctl_streamoff,
> +};
> +
> +/* ------------------------------------------------------------------------
> + * V4L2 File Operations
> + */
> +
> +static struct v4l2_file_operations uvc_meta_fops = {
> +	.owner = THIS_MODULE,
> +	.unlocked_ioctl = video_ioctl2,
> +	.open = v4l2_fh_open,
> +	.release = vb2_fop_release,
> +	.poll = vb2_fop_poll,
> +	.mmap = vb2_fop_mmap,
> +};
> +
> +int uvc_meta_register(struct uvc_streaming *stream)
> +{
> +	struct uvc_device *dev = stream->dev;
> +	struct uvc_meta_dev *meta = &stream->meta;
> +	struct video_device *vdev = &meta->vdev;
> +	struct uvc_video_queue *quvc = &meta->queue;
> +	struct vb2_queue *queue = &quvc->queue;
> +	int ret;
> +
> +	vdev->v4l2_dev = &dev->vdev;
> +	vdev->fops = &uvc_meta_fops;
> +	vdev->ioctl_ops = &uvc_meta_ioctl_ops;
> +	vdev->release = video_device_release_empty;
> +	vdev->prio = &stream->chain->prio;
> +	vdev->vfl_dir = VFL_DIR_RX;
> +	strlcpy(vdev->name, dev->name, sizeof(vdev->name));
> +
> +	video_set_drvdata(vdev, stream);
> +
> +	/* Initialize the video buffer queue. */
> +	queue->type = V4L2_BUF_TYPE_META_CAPTURE;
> +	queue->io_modes = VB2_MMAP | VB2_USERPTR;
> +	queue->drv_priv = quvc;
> +	queue->buf_struct_size = sizeof(struct uvc_buffer);
> +	queue->ops = &uvc_meta_queue_ops;
> +	queue->mem_ops = &vb2_vmalloc_memops;
> +	queue->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC
> +		| V4L2_BUF_FLAG_TSTAMP_SRC_SOE;
> +	queue->lock = &quvc->mutex;
> +	ret = vb2_queue_init(queue);
> +	if (ret < 0)
> +		return ret;
> +
> +	mutex_init(&quvc->mutex);
> +	spin_lock_init(&quvc->irqlock);
> +	INIT_LIST_HEAD(&quvc->irqqueue);
> +
> +	vdev->queue = queue;

You can set vdev->queue above with the rest of the vdev initialization. 

> +	ret = video_register_device(vdev, VFL_TYPE_GRABBER, -1);
> +	if (ret < 0)
> +		uvc_printk(KERN_ERR, "Failed to register metadata device (%d).
\n", ret);
> +
> +	return ret;
> +}
> diff --git a/drivers/media/usb/uvc/uvc_video.c
> b/drivers/media/usb/uvc/uvc_video.c index b5589d5..1bda8e1 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -1158,8 +1158,30 @@ static void uvc_video_validate_buffer(const struct
> uvc_streaming *stream, /*
>   * Completion handler for video URBs.
>   */
> +static void uvc_video_decode_meta(struct uvc_streaming *stream,
> +			struct uvc_buffer *buf, struct uvc_buffer *meta_buf,
> +			u8 *mem, int length)

I don't think length can be negative, you can make it an unsigned int and 
replace min_t with min below.

> +{
> +	size_t nbytes;
> +
> +	if (!meta_buf || !length)
> +		return;
> +
> +	nbytes = min_t(unsigned int, length, meta_buf->length);
> +
> +	meta_buf->buf.sequence = buf->buf.sequence;
> +	meta_buf->buf.field = buf->buf.field;
> +	meta_buf->buf.vb2_buf.timestamp = buf->buf.vb2_buf.timestamp;
> +
> +	memcpy(meta_buf->mem, mem, nbytes);

Do you need the whole header ? Shouldn't you strip the part already handled by 
the driver ?

> +	meta_buf->bytesused = nbytes;
> +	meta_buf->state = UVC_BUF_STATE_READY;
> +
> +	uvc_queue_next_buffer(&stream->meta.queue, meta_buf);

This essentially means that you'll need one buffer per isochronous packet. 
Given the number of isochronous packets that make a complete image the cost 
seem prohibitive to me. You should instead gather metadata from all headers 
into a single buffer.

> +}
> +
>  static void uvc_video_decode_isoc(struct urb *urb, struct uvc_streaming
> *stream,
> -	struct uvc_buffer *buf)
> +			struct uvc_buffer *buf, struct uvc_buffer *meta_buf)
>  {
>  	u8 *mem;
>  	int ret, i;
> @@ -1189,6 +1211,8 @@ static void uvc_video_decode_isoc(struct urb *urb,
> struct uvc_streaming *stream, if (ret < 0)
>  			continue;
> 
> +		uvc_video_decode_meta(stream, buf, meta_buf, mem, ret);
> +
>  		/* Decode the payload data. */
>  		uvc_video_decode_data(stream, buf, mem + ret,
>  			urb->iso_frame_desc[i].actual_length - ret);
> @@ -1205,7 +1229,7 @@ static void uvc_video_decode_isoc(struct urb *urb,
> struct uvc_streaming *stream, }
> 
>  static void uvc_video_decode_bulk(struct urb *urb, struct uvc_streaming
> *stream,
> -	struct uvc_buffer *buf)
> +			struct uvc_buffer *buf, struct uvc_buffer *meta_buf)
>  {
>  	u8 *mem;
>  	int len, ret;
> @@ -1239,6 +1263,8 @@ static void uvc_video_decode_bulk(struct urb *urb,
> struct uvc_streaming *stream, memcpy(stream->bulk.header, mem, ret);
>  			stream->bulk.header_size = ret;
> 
> +			uvc_video_decode_meta(stream, buf, meta_buf, mem, 
ret);
> +
>  			mem += ret;
>  			len -= ret;
>  		}
> @@ -1262,8 +1288,7 @@ static void uvc_video_decode_bulk(struct urb *urb,
> struct uvc_streaming *stream, uvc_video_decode_end(stream, buf,
> stream->bulk.header,
>  				stream->bulk.payload_size);
>  			if (buf->state == UVC_BUF_STATE_READY)
> -				buf = uvc_queue_next_buffer(&stream->queue,
> -							    buf);
> +				uvc_queue_next_buffer(&stream->queue, buf);

This could be split to a separate patch.

>  		}
> 
>  		stream->bulk.header_size = 0;
> @@ -1273,7 +1298,7 @@ static void uvc_video_decode_bulk(struct urb *urb,
> struct uvc_streaming *stream, }
> 
>  static void uvc_video_encode_bulk(struct urb *urb, struct uvc_streaming
> *stream,
> -	struct uvc_buffer *buf)
> +	struct uvc_buffer *buf, struct uvc_buffer *meta_buf)
>  {
>  	u8 *mem = urb->transfer_buffer;
>  	int len = stream->urb_size, ret;
> @@ -1319,7 +1344,8 @@ static void uvc_video_complete(struct urb *urb)
>  {
>  	struct uvc_streaming *stream = urb->context;
>  	struct uvc_video_queue *queue = &stream->queue;
> -	struct uvc_buffer *buf = NULL;
> +	struct uvc_video_queue *qmeta = &stream->meta.queue;
> +	struct uvc_buffer *buf = NULL, *buf_meta = NULL;

One variable per line please.

>  	unsigned long flags;
>  	int ret;
> 
> @@ -1338,6 +1364,7 @@ static void uvc_video_complete(struct urb *urb)
>  	case -ECONNRESET:	/* usb_unlink_urb() called. */
>  	case -ESHUTDOWN:	/* The endpoint is being disabled. */
>  		uvc_queue_cancel(queue, urb->status == -ESHUTDOWN);
> +		uvc_queue_cancel(qmeta, urb->status == -ESHUTDOWN);
>  		return;
>  	}
> 
> @@ -1347,7 +1374,13 @@ static void uvc_video_complete(struct urb *urb)
>  				       queue);
>  	spin_unlock_irqrestore(&queue->irqlock, flags);
> 
> -	stream->decode(urb, stream, buf);
> +	spin_lock_irqsave(&qmeta->irqlock, flags);
> +	if (!list_empty(&qmeta->irqqueue))
> +		buf_meta = list_first_entry(&qmeta->irqqueue, struct 
uvc_buffer,
> +					    queue);
> +	spin_unlock_irqrestore(&qmeta->irqlock, flags);
> +
> +	stream->decode(urb, stream, buf, buf_meta);
> 
>  	if ((ret = usb_submit_urb(urb, GFP_ATOMIC)) < 0) {
>  		uvc_printk(KERN_ERR, "Failed to resubmit video URB (%d).\n",
> diff --git a/drivers/media/usb/uvc/uvcvideo.h
> b/drivers/media/usb/uvc/uvcvideo.h index 3d6cc62..ebff4b6 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -464,6 +464,11 @@ struct uvc_stats_stream {
>  	unsigned int max_sof;		/* Maximum STC.SOF value */
>  };
> 
> +struct uvc_meta_dev {

All other structures use _device, not _dev. Let's be consistent.

> +	struct video_device vdev;
> +	struct uvc_video_queue queue;
> +};
> +
>  struct uvc_streaming {
>  	struct list_head list;
>  	struct uvc_device *dev;
> @@ -495,7 +500,9 @@ struct uvc_streaming {
>  	unsigned int frozen : 1;
>  	struct uvc_video_queue queue;
>  	void (*decode) (struct urb *urb, struct uvc_streaming *video,
> -			struct uvc_buffer *buf);
> +			struct uvc_buffer *buf, struct uvc_buffer *meta_buf);
> +
> +	struct uvc_meta_dev meta;
> 
>  	/* Context data used by the bulk completion handler. */
>  	struct {
> @@ -700,6 +707,7 @@ extern int uvc_query_ctrl(struct uvc_device *dev, __u8
> query, __u8 unit, void uvc_video_clock_update(struct uvc_streaming *stream,
>  			    struct vb2_v4l2_buffer *vbuf,
>  			    struct uvc_buffer *buf);
> +int uvc_meta_register(struct uvc_streaming *stream);
> 
>  /* Status */
>  extern int uvc_status_init(struct uvc_device *dev);
> @@ -754,7 +762,7 @@ extern struct usb_host_endpoint *uvc_find_endpoint(
> 
>  /* Quirks support */
>  void uvc_video_decode_isight(struct urb *urb, struct uvc_streaming *stream,
> -		struct uvc_buffer *buf);
> +		struct uvc_buffer *buf, struct uvc_buffer *meta_buf);
> 
>  /* debugfs and statistics */
>  int uvc_debugfs_init(void);
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c
> b/drivers/media/v4l2-core/v4l2-ioctl.c index 44a29af..1618be4 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -1232,6 +1232,7 @@ static void v4l_fill_fmtdesc(struct v4l2_fmtdesc *fmt)
> case V4L2_TCH_FMT_DELTA_TD08:	descr = "8-bit signed deltas"; break; case
> V4L2_TCH_FMT_TU16:		descr = "16-bit unsigned touch data"; break; 
case
> V4L2_TCH_FMT_TU08:		descr = "8-bit unsigned touch data"; break;
> +	case
> V4L2_META_FMT_UVC:		descr = "UVC payload header metadata"; break;
> 
>  	default:
>  		/* Compressed formats */
> diff --git a/include/uapi/linux/uvcvideo.h b/include/uapi/linux/uvcvideo.h
> index 3b08186..e98de14 100644
> --- a/include/uapi/linux/uvcvideo.h
> +++ b/include/uapi/linux/uvcvideo.h
> @@ -67,4 +67,14 @@ struct uvc_xu_control_query {
>  #define UVCIOC_CTRL_MAP		_IOWR('u', 0x20, struct 
uvc_xu_control_mapping)
>  #define UVCIOC_CTRL_QUERY	_IOWR('u', 0x21, struct uvc_xu_control_query)
> 
> +/*
> + * Metadata node
> + */
> +
> +/*
> + * Actually 255 bytes, but 256 is just a nicer number. We keep the buffer
> size
> + * constant and just set .usedbytes accordingly
> + */
> +#define UVC_PAYLOAD_HEADER_MAX_SIZE 256

Why is lying about the size better ?

>  #endif
Guennadi Liakhovetski - Dec. 5, 2016, 3:35 p.m.
Hi Laurent,

Thanks for the review! I'll work to address your comments. A couple of 
clarifications:

On Mon, 5 Dec 2016, Laurent Pinchart wrote:

> Hi Guennadi,
> 
> Thank you for the patch.
> 
> On Friday 02 Dec 2016 11:53:23 Guennadi Liakhovetski wrote:
> > Some UVC video cameras contain metadata in their payload headers. This
> > patch extracts that data, skipping the standard part of the header, on
> > both bulk and isochronous endpoints and makes it available to the user
> > space on a separate video node, using the V4L2_CAP_META_CAPTURE
> > capability and the V4L2_BUF_TYPE_META_CAPTURE buffer queue type. Even
> > though different cameras will have different metadata formats, we use
> > the same V4L2_META_FMT_UVC pixel format for all of them. Users have to
> > parse data, based on the specific camera model information.
> > 
> > Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@intel.com>
> > ---
> > 
> > v2:
> > - updated to the current media/master
> > - removed superfluous META capability from capture nodes
> > - now the complete UVC payload header is copied to buffers, including
> >   standard fields
> > 
> > Still open for discussion: is this really OK to always create an
> > additional metadata node for each UVC camera or UVC video interface.

[snip]

> > +	/*
> > +	 * Register a metadata node. TODO: shall this only be enabled for some
> > +	 * cameras?
> > +	 */
> > +	if (!(dev->quirks & UVC_QUIRK_BUILTIN_ISIGHT))
> > +		uvc_meta_register(stream);
> > +
> 
> I think so, only for the cameras that can produce metadata.

Every UVC camera produces metadata, but most cameras only have standard 
fields there. Whether we should stream standard header fields from the 
metadata node will be discussed later. If we do decide to stream standard 
header fields, then every USB camera gets metadata nodes. If we decide not 
to include standard fields, how do we know whether the camera has any 
private fields in headers without streaming from it? Do you want a quirk 
for such cameras?

[snip]

> > +static struct vb2_ops uvc_meta_queue_ops = {
> > +	.queue_setup = meta_queue_setup,
> > +	.buf_prepare = meta_buffer_prepare,
> > +	.buf_queue = meta_buffer_queue,
> > +	.wait_prepare = vb2_ops_wait_prepare,
> > +	.wait_finish = vb2_ops_wait_finish,
> > +	.start_streaming = meta_start_streaming,
> > +	.stop_streaming = meta_stop_streaming,
> > +};
> 
> How about reusing the uvc_queue.c implementation, with a few new checks for 
> metadata buffers where needed, instead of duplicating code ? At first sight 
> the changes don't seem to be too intrusive (but I might have overlooked 
> something).

I thought about that in the beginning and even started implementing it 
that way, but at some point it became too inconvenient, so, I switched 
over to a separate implementation. I'll think about it more and either 
explain, why I didn't want to do that, or unite them.

[snip]

> > +{
> > +	size_t nbytes;
> > +
> > +	if (!meta_buf || !length)
> > +		return;
> > +
> > +	nbytes = min_t(unsigned int, length, meta_buf->length);
> > +
> > +	meta_buf->buf.sequence = buf->buf.sequence;
> > +	meta_buf->buf.field = buf->buf.field;
> > +	meta_buf->buf.vb2_buf.timestamp = buf->buf.vb2_buf.timestamp;
> > +
> > +	memcpy(meta_buf->mem, mem, nbytes);
> 
> Do you need the whole header ? Shouldn't you strip the part already handled by 
> the driver ?

My original version did that, but we also need the timestamp from the 
header. The driver does parse it, but the implementation there has 
multiple times been reported as buggy and noone has been able to fix it so 
far :) So, I ended up pulling the complete header to the user-space. 
Unless time-stamp processing is fixed in the kernel, I don't think we can 
frop this.

> > +	meta_buf->bytesused = nbytes;
> > +	meta_buf->state = UVC_BUF_STATE_READY;
> > +
> > +	uvc_queue_next_buffer(&stream->meta.queue, meta_buf);
> 
> This essentially means that you'll need one buffer per isochronous packet. 
> Given the number of isochronous packets that make a complete image the cost 
> seem prohibitive to me. You should instead gather metadata from all headers 
> into a single buffer.

Hm, I only worked with cameras, using bulk transfers, so, didn't consider 
ISOC implications. Will have to think about this.

[snip]

Thanks
Guennadi
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Laurent Pinchart - Dec. 5, 2016, 10:06 p.m.
Hi Guennadi,

On Monday 05 Dec 2016 16:35:39 Guennadi Liakhovetski wrote:
> On Mon, 5 Dec 2016, Laurent Pinchart wrote:
> > On Friday 02 Dec 2016 11:53:23 Guennadi Liakhovetski wrote:
> >> Some UVC video cameras contain metadata in their payload headers. This
> >> patch extracts that data, skipping the standard part of the header, on
> >> both bulk and isochronous endpoints and makes it available to the user
> >> space on a separate video node, using the V4L2_CAP_META_CAPTURE
> >> capability and the V4L2_BUF_TYPE_META_CAPTURE buffer queue type. Even
> >> though different cameras will have different metadata formats, we use
> >> the same V4L2_META_FMT_UVC pixel format for all of them. Users have to
> >> parse data, based on the specific camera model information.
> >> 
> >> Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@intel.com>
> >> ---
> >> 
> >> v2:
> >> - updated to the current media/master
> >> - removed superfluous META capability from capture nodes
> >> - now the complete UVC payload header is copied to buffers, including
> >>   standard fields
> >> 
> >> Still open for discussion: is this really OK to always create an
> >> additional metadata node for each UVC camera or UVC video interface.
> 
> [snip]
> 
> >> +	/*
> >> +	 * Register a metadata node. TODO: shall this only be enabled for some
> >> +	 * cameras?
> >> +	 */
> >> +	if (!(dev->quirks & UVC_QUIRK_BUILTIN_ISIGHT))
> >> +		uvc_meta_register(stream);
> >> +
> > 
> > I think so, only for the cameras that can produce metadata.
> 
> Every UVC camera produces metadata, but most cameras only have standard
> fields there. Whether we should stream standard header fields from the
> metadata node will be discussed later. If we do decide to stream standard
> header fields, then every USB camera gets metadata nodes. If we decide not
> to include standard fields, how do we know whether the camera has any
> private fields in headers without streaming from it? Do you want a quirk
> for such cameras?

Unless they can be detected in a standard way that's probably the best 
solution. Please remember that the UVC specification doesn't allow vendors to 
extend headers in a vendor-specific way. This is an abuse of the 
specification, so a quirk is probably the best option.

> [snip]
> 
> > > +static struct vb2_ops uvc_meta_queue_ops = {
> > > +	.queue_setup = meta_queue_setup,
> > > +	.buf_prepare = meta_buffer_prepare,
> > > +	.buf_queue = meta_buffer_queue,
> > > +	.wait_prepare = vb2_ops_wait_prepare,
> > > +	.wait_finish = vb2_ops_wait_finish,
> > > +	.start_streaming = meta_start_streaming,
> > > +	.stop_streaming = meta_stop_streaming,
> > > +};
> > 
> > How about reusing the uvc_queue.c implementation, with a few new checks
> > for metadata buffers where needed, instead of duplicating code ? At first
> > sight the changes don't seem to be too intrusive (but I might have
> > overlooked something).
> 
> I thought about that in the beginning and even started implementing it
> that way, but at some point it became too inconvenient, so, I switched
> over to a separate implementation. I'll think about it more and either
> explain, why I didn't want to do that, or unite them.
> 
> [snip]
> 
> > > +{
> > > +	size_t nbytes;
> > > +
> > > +	if (!meta_buf || !length)
> > > +		return;
> > > +
> > > +	nbytes = min_t(unsigned int, length, meta_buf->length);
> > > +
> > > +	meta_buf->buf.sequence = buf->buf.sequence;
> > > +	meta_buf->buf.field = buf->buf.field;
> > > +	meta_buf->buf.vb2_buf.timestamp = buf->buf.vb2_buf.timestamp;
> > > +
> > > +	memcpy(meta_buf->mem, mem, nbytes);
> > 
> > Do you need the whole header ? Shouldn't you strip the part already
> > handled by the driver ?
> 
> My original version did that, but we also need the timestamp from the
> header. The driver does parse it, but the implementation there has
> multiple times been reported as buggy and noone has been able to fix it so
> far :)

-ENOTIME I'm afraid, but feel free to give it a go :-) On the other hand 
supplying the PTS and SCR values to userspace would be useful to implement a 
high-accuracy clock translation algorithm that could make use of floating 
point operations.

> So, I ended up pulling the complete header to the user-space. Unless time-
> stamp processing is fixed in the kernel, I don't think we can frop this.

SCR and PTS should be provided to userspace in a standard way.

> >> +	meta_buf->bytesused = nbytes;
> >> +	meta_buf->state = UVC_BUF_STATE_READY;
> >> +
> >> +	uvc_queue_next_buffer(&stream->meta.queue, meta_buf);
> > 
> > This essentially means that you'll need one buffer per isochronous packet.
> > Given the number of isochronous packets that make a complete image the
> > cost seem prohibitive to me. You should instead gather metadata from all
> > headers into a single buffer.
> 
> Hm, I only worked with cameras, using bulk transfers, so, didn't consider
> ISOC implications. Will have to think about this.
Guennadi Liakhovetski - Dec. 5, 2016, 10:13 p.m.
Just one question:

On Tue, 6 Dec 2016, Laurent Pinchart wrote:

> > >> +	/*
> > >> +	 * Register a metadata node. TODO: shall this only be enabled for some
> > >> +	 * cameras?
> > >> +	 */
> > >> +	if (!(dev->quirks & UVC_QUIRK_BUILTIN_ISIGHT))
> > >> +		uvc_meta_register(stream);
> > >> +
> > > 
> > > I think so, only for the cameras that can produce metadata.
> > 
> > Every UVC camera produces metadata, but most cameras only have standard
> > fields there. Whether we should stream standard header fields from the
> > metadata node will be discussed later. If we do decide to stream standard
> > header fields, then every USB camera gets metadata nodes. If we decide not
> > to include standard fields, how do we know whether the camera has any
> > private fields in headers without streaming from it? Do you want a quirk
> > for such cameras?
> 
> Unless they can be detected in a standard way that's probably the best 
> solution. Please remember that the UVC specification doesn't allow vendors to 
> extend headers in a vendor-specific way.

Does it not? Where is that specified? I didn't find that anywhere.

Thanks
Guennadi
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Laurent Pinchart - Dec. 5, 2016, 10:25 p.m.
Hi Guennadi,

On Monday 05 Dec 2016 23:13:53 Guennadi Liakhovetski wrote:
> Just one question:
> 
> On Tue, 6 Dec 2016, Laurent Pinchart wrote:
> >>>> +	/*
> >>>> +	 * Register a metadata node. TODO: shall this only be enabled
> >>>> for some
> >>>> +	 * cameras?
> >>>> +	 */
> >>>> +	if (!(dev->quirks & UVC_QUIRK_BUILTIN_ISIGHT))
> >>>> +		uvc_meta_register(stream);
> >>>> +
> >>> 
> >>> I think so, only for the cameras that can produce metadata.
> >> 
> >> Every UVC camera produces metadata, but most cameras only have standard
> >> fields there. Whether we should stream standard header fields from the
> >> metadata node will be discussed later. If we do decide to stream
> >> standard header fields, then every USB camera gets metadata nodes. If we
> >> decide not to include standard fields, how do we know whether the camera
> >> has any private fields in headers without streaming from it? Do you want
> >> a quirk for such cameras?
> > 
> > Unless they can be detected in a standard way that's probably the best
> > solution. Please remember that the UVC specification doesn't allow vendors
> > to extend headers in a vendor-specific way.
> 
> Does it not? Where is that specified? I didn't find that anywhere.

It's the other way around, it document a standard way to extend the payload 
header. Any option you pick risks being incompatible with future revisions of 
the specification. For instance the payload header's bmHeaderInfo field can be 
extended through the use of the EOF bit, but a future version of the 
specification could also extend it, in a way that would make a vendor-specific 
extension be mistaken for the standard extension.

Now, you could add data after the standard payload without touching the 
bmHeaderInfo field, but I'm still worried it could be broken by future 
versions of the specification.
Guennadi Liakhovetski - Dec. 6, 2016, 10:39 a.m.
Hi Laurent,

On Tue, 6 Dec 2016, Laurent Pinchart wrote:

> Hi Guennadi,
> 
> On Monday 05 Dec 2016 23:13:53 Guennadi Liakhovetski wrote:
> > Just one question:
> > 
> > On Tue, 6 Dec 2016, Laurent Pinchart wrote:
> > >>>> +	/*
> > >>>> +	 * Register a metadata node. TODO: shall this only be enabled
> > >>>> for some
> > >>>> +	 * cameras?
> > >>>> +	 */
> > >>>> +	if (!(dev->quirks & UVC_QUIRK_BUILTIN_ISIGHT))
> > >>>> +		uvc_meta_register(stream);
> > >>>> +
> > >>> 
> > >>> I think so, only for the cameras that can produce metadata.
> > >> 
> > >> Every UVC camera produces metadata, but most cameras only have standard
> > >> fields there. Whether we should stream standard header fields from the
> > >> metadata node will be discussed later. If we do decide to stream
> > >> standard header fields, then every USB camera gets metadata nodes. If we
> > >> decide not to include standard fields, how do we know whether the camera
> > >> has any private fields in headers without streaming from it? Do you want
> > >> a quirk for such cameras?
> > > 
> > > Unless they can be detected in a standard way that's probably the best
> > > solution. Please remember that the UVC specification doesn't allow vendors
> > > to extend headers in a vendor-specific way.
> > 
> > Does it not? Where is that specified? I didn't find that anywhere.
> 
> It's the other way around, it document a standard way to extend the payload 
> header. Any option you pick risks being incompatible with future revisions of 
> the specification. For instance the payload header's bmHeaderInfo field can be 
> extended through the use of the EOF bit, but a future version of the 
> specification could also extend it, in a way that would make a vendor-specific 
> extension be mistaken for the standard extension.
> 
> Now, you could add data after the standard payload without touching the 
> bmHeaderInfo field, but I'm still worried it could be broken by future 
> versions of the specification.

Exactly - using "free" space in payload headers is not a part of the spec, 
but is also not prohibited by it. As for future versions - cameras specify 
which version of the spec they implement, and existing versions cannot 
change. If a camera decides to upgrade and in future UVC versions there 
won't be enough space left for the private data, only then the camera 
manufacturer will have a problem, that they will have to solve. The 
user-space software will have to know, that UVC 5.1 metadata has a 
different format, than UVC 1.5, that's true.

Thanks
Guennadi
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Laurent Pinchart - Dec. 6, 2016, 3:56 p.m.
Hi Guennadi,

On Tuesday 06 Dec 2016 11:39:22 Guennadi Liakhovetski wrote:
> On Tue, 6 Dec 2016, Laurent Pinchart wrote:
> > On Monday 05 Dec 2016 23:13:53 Guennadi Liakhovetski wrote:
> >> On Tue, 6 Dec 2016, Laurent Pinchart wrote:
> >>>>>> +	/*
> >>>>>> +	 * Register a metadata node. TODO: shall this only be enabled
> >>>>>> for some
> >>>>>> +	 * cameras?
> >>>>>> +	 */
> >>>>>> +	if (!(dev->quirks & UVC_QUIRK_BUILTIN_ISIGHT))
> >>>>>> +		uvc_meta_register(stream);
> >>>>>> +
> >>>>> 
> >>>>> I think so, only for the cameras that can produce metadata.
> >>>> 
> >>>> Every UVC camera produces metadata, but most cameras only have standard
> >>>> fields there. Whether we should stream standard header fields from the
> >>>> metadata node will be discussed later. If we do decide to stream
> >>>> standard header fields, then every USB camera gets metadata nodes. If
> >>>> we decide not to include standard fields, how do we know whether the
> >>>> camera has any private fields in headers without streaming from it? Do
> >>>> you want a quirk for such cameras?
> >>> 
> >>> Unless they can be detected in a standard way that's probably the best
> >>> solution. Please remember that the UVC specification doesn't allow
> >>> vendors to extend headers in a vendor-specific way.
> >> 
> >> Does it not? Where is that specified? I didn't find that anywhere.
> > 
> > It's the other way around, it document a standard way to extend the
> > payload header. Any option you pick risks being incompatible with future
> > revisions of the specification. For instance the payload header's
> > bmHeaderInfo field can be extended through the use of the EOF bit, but a
> > future version of the specification could also extend it, in a way that
> > would make a vendor-specific extension be mistaken for the standard
> > extension.
> > 
> > Now, you could add data after the standard payload without touching the
> > bmHeaderInfo field, but I'm still worried it could be broken by future
> > versions of the specification.
> 
> Exactly - using "free" space in payload headers is not a part of the spec,
> but is also not prohibited by it. As for future versions - cameras specify
> which version of the spec they implement, and existing versions cannot
> change. If a camera decides to upgrade and in future UVC versions there
> won't be enough space left for the private data, only then the camera
> manufacturer will have a problem, that they will have to solve. The
> user-space software will have to know, that UVC 5.1 metadata has a
> different format, than UVC 1.5, that's true.

I agree that the specification doesn't explicitly forbid it, but it's a very 
grey area. An extension mechanism should be standardized by the USB-IF UVC 
working group. I'd propose it myself if they hadn't decided to kick me out 
years ago :-)
Guennadi Liakhovetski - Dec. 8, 2016, 1:34 p.m.
Hi Laurent,

One more question:

On Tue, 6 Dec 2016, Laurent Pinchart wrote:

> Hi Guennadi,
> 
> On Tuesday 06 Dec 2016 11:39:22 Guennadi Liakhovetski wrote:
> > On Tue, 6 Dec 2016, Laurent Pinchart wrote:
> > > On Monday 05 Dec 2016 23:13:53 Guennadi Liakhovetski wrote:
> > >> On Tue, 6 Dec 2016, Laurent Pinchart wrote:
> > >>>>>> +	/*
> > >>>>>> +	 * Register a metadata node. TODO: shall this only be enabled
> > >>>>>> for some
> > >>>>>> +	 * cameras?
> > >>>>>> +	 */
> > >>>>>> +	if (!(dev->quirks & UVC_QUIRK_BUILTIN_ISIGHT))
> > >>>>>> +		uvc_meta_register(stream);
> > >>>>>> +
> > >>>>> 
> > >>>>> I think so, only for the cameras that can produce metadata.
> > >>>> 
> > >>>> Every UVC camera produces metadata, but most cameras only have standard
> > >>>> fields there. Whether we should stream standard header fields from the
> > >>>> metadata node will be discussed later. If we do decide to stream
> > >>>> standard header fields, then every USB camera gets metadata nodes. If
> > >>>> we decide not to include standard fields, how do we know whether the
> > >>>> camera has any private fields in headers without streaming from it? Do
> > >>>> you want a quirk for such cameras?
> > >>> 
> > >>> Unless they can be detected in a standard way that's probably the best
> > >>> solution.

How about a module parameter with a list of VID:PID pairs? The problem 
with the quirk is, that as vendors produce multiple cameras with different 
PIDs they will have to push patches for each such camera.

Thanks
Guennadi
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Laurent Pinchart - Dec. 8, 2016, 1:39 p.m.
Hi Guennadi,

On Thursday 08 Dec 2016 14:34:46 Guennadi Liakhovetski wrote:
> On Tue, 6 Dec 2016, Laurent Pinchart wrote:
> > On Tuesday 06 Dec 2016 11:39:22 Guennadi Liakhovetski wrote:
> >> On Tue, 6 Dec 2016, Laurent Pinchart wrote:
> >>> On Monday 05 Dec 2016 23:13:53 Guennadi Liakhovetski wrote:
> >>>> On Tue, 6 Dec 2016, Laurent Pinchart wrote:
> >>>>>>>> +	/*
> >>>>>>>> +	 * Register a metadata node. TODO: shall this only be enabled
> >>>>>>>> for some
> >>>>>>>> +	 * cameras?
> >>>>>>>> +	 */
> >>>>>>>> +	if (!(dev->quirks & UVC_QUIRK_BUILTIN_ISIGHT))
> >>>>>>>> +		uvc_meta_register(stream);
> >>>>>>>> +
> >>>>>>> 
> >>>>>>> I think so, only for the cameras that can produce metadata.
> >>>>>> 
> >>>>>> Every UVC camera produces metadata, but most cameras only have
> >>>>>> standard fields there. Whether we should stream standard header
> >>>>>> fields from the metadata node will be discussed later. If we do
> >>>>>> decide to stream standard header fields, then every USB camera gets
> >>>>>> metadata nodes. If we decide not to include standard fields, how do
> >>>>>> we know whether the camera has any private fields in headers
> >>>>>> without streaming from it? Do you want a quirk for such cameras?
> >>>>> 
> >>>>> Unless they can be detected in a standard way that's probably the
> >>>>> best solution.
> 
> How about a module parameter with a list of VID:PID pairs?

I'd like something that works out of the box for end-users, at least in most 
cases. There's already a way to set quirks through a module parameter, and I 
think I'd accept a patch extending that it make it VID:PID dependent. That's 
an acceptable solution for testing, but should not be considered as the way to 
go for production.

> The problem with the quirk is, that as vendors produce multiple cameras with
> different PIDs they will have to push patches for each such camera.

How many such devices do you expect ?
Guennadi Liakhovetski - Dec. 8, 2016, 3:18 p.m.
On Thu, 8 Dec 2016, Laurent Pinchart wrote:

> Hi Guennadi,
> 
> On Thursday 08 Dec 2016 14:34:46 Guennadi Liakhovetski wrote:
> > On Tue, 6 Dec 2016, Laurent Pinchart wrote:
> > > On Tuesday 06 Dec 2016 11:39:22 Guennadi Liakhovetski wrote:
> > >> On Tue, 6 Dec 2016, Laurent Pinchart wrote:
> > >>> On Monday 05 Dec 2016 23:13:53 Guennadi Liakhovetski wrote:
> > >>>> On Tue, 6 Dec 2016, Laurent Pinchart wrote:
> > >>>>>>>> +	/*
> > >>>>>>>> +	 * Register a metadata node. TODO: shall this only be enabled
> > >>>>>>>> for some
> > >>>>>>>> +	 * cameras?
> > >>>>>>>> +	 */
> > >>>>>>>> +	if (!(dev->quirks & UVC_QUIRK_BUILTIN_ISIGHT))
> > >>>>>>>> +		uvc_meta_register(stream);
> > >>>>>>>> +
> > >>>>>>> 
> > >>>>>>> I think so, only for the cameras that can produce metadata.
> > >>>>>> 
> > >>>>>> Every UVC camera produces metadata, but most cameras only have
> > >>>>>> standard fields there. Whether we should stream standard header
> > >>>>>> fields from the metadata node will be discussed later. If we do
> > >>>>>> decide to stream standard header fields, then every USB camera gets
> > >>>>>> metadata nodes. If we decide not to include standard fields, how do
> > >>>>>> we know whether the camera has any private fields in headers
> > >>>>>> without streaming from it? Do you want a quirk for such cameras?
> > >>>>> 
> > >>>>> Unless they can be detected in a standard way that's probably the
> > >>>>> best solution.
> > 
> > How about a module parameter with a list of VID:PID pairs?
> 
> I'd like something that works out of the box for end-users, at least in most 
> cases. There's already a way to set quirks through a module parameter, and I 
> think I'd accept a patch extending that it make it VID:PID dependent.

Ok, that helps already, sure.

> That's 
> an acceptable solution for testing, but should not be considered as the way to 
> go for production.
> 
> > The problem with the quirk is, that as vendors produce multiple cameras with
> > different PIDs they will have to push patches for each such camera.
> 
> How many such devices do you expect ?

No idea, significantly more than 2, let's say :) But well, you already can 
count a few RealSense USB / UVC cameras on the market.

Concerning metadata for isochronous endpoints. I actually don't know what 
to do with it. I don't have any such cameras with non-standard metadata. 
For the standard metadata it would probably be enough to get either the 
first or the last or the middle payload. Collecting all of them seems 
redundant to me. Maybe I could for now only enable metadata nodes for bulk 
endpoints. Would that be acceptable?

Thanks
Guennadi
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Patch

diff --git a/drivers/media/usb/uvc/Makefile b/drivers/media/usb/uvc/Makefile
index c26d12f..06c7cd3 100644
--- a/drivers/media/usb/uvc/Makefile
+++ b/drivers/media/usb/uvc/Makefile
@@ -1,5 +1,5 @@ 
 uvcvideo-objs  := uvc_driver.o uvc_queue.o uvc_v4l2.o uvc_video.o uvc_ctrl.o \
-		  uvc_status.o uvc_isight.o uvc_debugfs.o
+		  uvc_status.o uvc_isight.o uvc_debugfs.o uvc_metadata.o
 ifeq ($(CONFIG_MEDIA_CONTROLLER),y)
 uvcvideo-objs  += uvc_entity.o
 endif
diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index 04bf350..edb67ac 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -1866,6 +1866,9 @@  static void uvc_unregister_video(struct uvc_device *dev)
 
 		video_unregister_device(&stream->vdev);
 
+		if (video_is_registered(&stream->meta.vdev))
+			video_unregister_device(&stream->meta.vdev);
+
 		uvc_debugfs_cleanup_stream(stream);
 	}
 
@@ -1926,6 +1929,13 @@  static int uvc_register_video(struct uvc_device *dev,
 		return ret;
 	}
 
+	/*
+	 * Register a metadata node. TODO: shall this only be enabled for some
+	 * cameras?
+	 */
+	if (!(dev->quirks & UVC_QUIRK_BUILTIN_ISIGHT))
+		uvc_meta_register(stream);
+
 	if (stream->type == V4L2_BUF_TYPE_VIDEO_CAPTURE)
 		stream->chain->caps |= V4L2_CAP_VIDEO_CAPTURE;
 	else
diff --git a/drivers/media/usb/uvc/uvc_isight.c b/drivers/media/usb/uvc/uvc_isight.c
index 8510e725..fb940cf 100644
--- a/drivers/media/usb/uvc/uvc_isight.c
+++ b/drivers/media/usb/uvc/uvc_isight.c
@@ -100,7 +100,7 @@  static int isight_decode(struct uvc_video_queue *queue, struct uvc_buffer *buf,
 }
 
 void uvc_video_decode_isight(struct urb *urb, struct uvc_streaming *stream,
-		struct uvc_buffer *buf)
+			struct uvc_buffer *buf, struct uvc_buffer *meta_buf)
 {
 	int ret, i;
 
diff --git a/drivers/media/usb/uvc/uvc_metadata.c b/drivers/media/usb/uvc/uvc_metadata.c
new file mode 100644
index 0000000..ddf77d9
--- /dev/null
+++ b/drivers/media/usb/uvc/uvc_metadata.c
@@ -0,0 +1,228 @@ 
+/*
+ *      uvc_metadata.c  --  USB Video Class driver - Metadata handling
+ *
+ *      Copyright (C) 2016
+ *          Guennadi Liakhovetski (guennadi.liakhovetski@intel.com)
+ *
+ *      This program is free software; you can redistribute it and/or modify
+ *      it under the terms of the GNU General Public License as published by
+ *      the Free Software Foundation; either version 2 of the License, or
+ *      (at your option) any later version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/usb.h>
+#include <linux/videodev2.h>
+
+#include <media/v4l2-ioctl.h>
+#include <media/videobuf2-v4l2.h>
+#include <media/videobuf2-vmalloc.h>
+
+#include "uvcvideo.h"
+
+static inline struct uvc_buffer *to_uvc_buffer(struct vb2_v4l2_buffer *vbuf)
+{
+	return container_of(vbuf, struct uvc_buffer, buf);
+}
+
+/* -----------------------------------------------------------------------------
+ * videobuf2 Queue Operations
+ */
+
+static int meta_queue_setup(struct vb2_queue *vq, unsigned int *nbuffers,
+			    unsigned int *nplanes, unsigned int sizes[],
+			    struct device *alloc_devs[])
+{
+	if (*nplanes) {
+		if (*nplanes != 1)
+			return -EINVAL;
+
+		if (sizes[0] < UVC_PAYLOAD_HEADER_MAX_SIZE)
+			return -EINVAL;
+
+		return 0;
+	}
+
+	*nplanes = 1;
+	sizes[0] = UVC_PAYLOAD_HEADER_MAX_SIZE;
+
+	return 0;
+}
+
+static int meta_buffer_prepare(struct vb2_buffer *vb)
+{
+	struct vb2_v4l2_buffer *vbuf = to_vb2_v4l2_buffer(vb);
+	struct uvc_buffer *buf = to_uvc_buffer(vbuf);
+
+	if (vb->num_planes != 1)
+		return -EINVAL;
+
+	if (vb2_plane_size(vb, 0) < UVC_PAYLOAD_HEADER_MAX_SIZE)
+		return -EINVAL;
+
+	buf->state = UVC_BUF_STATE_QUEUED;
+	buf->error = 0;
+	buf->mem = vb2_plane_vaddr(vb, 0);
+	buf->length = vb2_plane_size(vb, 0);
+	buf->bytesused = 0;
+
+	return 0;
+}
+
+static void meta_buffer_queue(struct vb2_buffer *vb)
+{
+	struct vb2_v4l2_buffer *vbuf = to_vb2_v4l2_buffer(vb);
+	struct uvc_video_queue *queue = vb2_get_drv_priv(vb->vb2_queue);
+	struct uvc_buffer *buf = to_uvc_buffer(vbuf);
+	unsigned long flags;
+
+	spin_lock_irqsave(&queue->irqlock, flags);
+	list_add_tail(&buf->queue, &queue->irqqueue);
+	spin_unlock_irqrestore(&queue->irqlock, flags);
+}
+
+static int meta_start_streaming(struct vb2_queue *vq, unsigned int count)
+{
+	return 0;
+}
+
+static void meta_stop_streaming(struct vb2_queue *vq)
+{
+	struct uvc_video_queue *queue = vb2_get_drv_priv(vq);
+	struct uvc_buffer *buffer;
+	unsigned long flags;
+
+	spin_lock_irqsave(&queue->irqlock, flags);
+
+	/* Remove all buffers from the IRQ queue. */
+	list_for_each_entry(buffer, &queue->irqqueue, queue)
+		vb2_buffer_done(&buffer->buf.vb2_buf, VB2_BUF_STATE_ERROR);
+	INIT_LIST_HEAD(&queue->irqqueue);
+
+	spin_unlock_irqrestore(&queue->irqlock, flags);
+}
+
+static struct vb2_ops uvc_meta_queue_ops = {
+	.queue_setup = meta_queue_setup,
+	.buf_prepare = meta_buffer_prepare,
+	.buf_queue = meta_buffer_queue,
+	.wait_prepare = vb2_ops_wait_prepare,
+	.wait_finish = vb2_ops_wait_finish,
+	.start_streaming = meta_start_streaming,
+	.stop_streaming = meta_stop_streaming,
+};
+
+/* -----------------------------------------------------------------------------
+ * V4L2 ioctls
+ */
+
+static int meta_v4l2_querycap(struct file *file, void *fh,
+			      struct v4l2_capability *cap)
+{
+	struct v4l2_fh *vfh = file->private_data;
+	struct uvc_streaming *stream = video_get_drvdata(vfh->vdev);
+
+	cap->device_caps = V4L2_CAP_META_CAPTURE
+			 | V4L2_CAP_STREAMING;
+	cap->capabilities = V4L2_CAP_DEVICE_CAPS | cap->device_caps
+			  | stream->chain->caps;
+
+	strlcpy(cap->driver, "uvcvideo", sizeof(cap->driver));
+	strlcpy(cap->card, vfh->vdev->name, sizeof(cap->card));
+	usb_make_path(stream->dev->udev, cap->bus_info, sizeof(cap->bus_info));
+
+	return 0;
+}
+
+static int meta_v4l2_get_format(struct file *file, void *fh,
+				struct v4l2_format *format)
+{
+	struct v4l2_fh *vfh = file->private_data;
+	struct v4l2_meta_format *fmt = &format->fmt.meta;
+
+	if (format->type != vfh->vdev->queue->type)
+		return -EINVAL;
+
+	memset(fmt, 0, sizeof(*fmt));
+
+	fmt->dataformat = V4L2_META_FMT_UVC;
+	fmt->buffersize = UVC_PAYLOAD_HEADER_MAX_SIZE;
+
+	return 0;
+}
+
+static const struct v4l2_ioctl_ops uvc_meta_ioctl_ops = {
+	.vidioc_querycap		= meta_v4l2_querycap,
+	.vidioc_g_fmt_meta_cap		= meta_v4l2_get_format,
+	.vidioc_s_fmt_meta_cap		= meta_v4l2_get_format,
+	.vidioc_try_fmt_meta_cap	= meta_v4l2_get_format,
+	.vidioc_reqbufs			= vb2_ioctl_reqbufs,
+	.vidioc_querybuf		= vb2_ioctl_querybuf,
+	.vidioc_qbuf			= vb2_ioctl_qbuf,
+	.vidioc_dqbuf			= vb2_ioctl_dqbuf,
+	.vidioc_create_bufs		= vb2_ioctl_create_bufs,
+	.vidioc_prepare_buf		= vb2_ioctl_prepare_buf,
+	.vidioc_streamon		= vb2_ioctl_streamon,
+	.vidioc_streamoff		= vb2_ioctl_streamoff,
+};
+
+/* -----------------------------------------------------------------------------
+ * V4L2 File Operations
+ */
+
+static struct v4l2_file_operations uvc_meta_fops = {
+	.owner = THIS_MODULE,
+	.unlocked_ioctl = video_ioctl2,
+	.open = v4l2_fh_open,
+	.release = vb2_fop_release,
+	.poll = vb2_fop_poll,
+	.mmap = vb2_fop_mmap,
+};
+
+int uvc_meta_register(struct uvc_streaming *stream)
+{
+	struct uvc_device *dev = stream->dev;
+	struct uvc_meta_dev *meta = &stream->meta;
+	struct video_device *vdev = &meta->vdev;
+	struct uvc_video_queue *quvc = &meta->queue;
+	struct vb2_queue *queue = &quvc->queue;
+	int ret;
+
+	vdev->v4l2_dev = &dev->vdev;
+	vdev->fops = &uvc_meta_fops;
+	vdev->ioctl_ops = &uvc_meta_ioctl_ops;
+	vdev->release = video_device_release_empty;
+	vdev->prio = &stream->chain->prio;
+	vdev->vfl_dir = VFL_DIR_RX;
+	strlcpy(vdev->name, dev->name, sizeof(vdev->name));
+
+	video_set_drvdata(vdev, stream);
+
+	/* Initialize the video buffer queue. */
+	queue->type = V4L2_BUF_TYPE_META_CAPTURE;
+	queue->io_modes = VB2_MMAP | VB2_USERPTR;
+	queue->drv_priv = quvc;
+	queue->buf_struct_size = sizeof(struct uvc_buffer);
+	queue->ops = &uvc_meta_queue_ops;
+	queue->mem_ops = &vb2_vmalloc_memops;
+	queue->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC
+		| V4L2_BUF_FLAG_TSTAMP_SRC_SOE;
+	queue->lock = &quvc->mutex;
+	ret = vb2_queue_init(queue);
+	if (ret < 0)
+		return ret;
+
+	mutex_init(&quvc->mutex);
+	spin_lock_init(&quvc->irqlock);
+	INIT_LIST_HEAD(&quvc->irqqueue);
+
+	vdev->queue = queue;
+
+	ret = video_register_device(vdev, VFL_TYPE_GRABBER, -1);
+	if (ret < 0)
+		uvc_printk(KERN_ERR, "Failed to register metadata device (%d).\n", ret);
+
+	return ret;
+}
diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index b5589d5..1bda8e1 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -1158,8 +1158,30 @@  static void uvc_video_validate_buffer(const struct uvc_streaming *stream,
 /*
  * Completion handler for video URBs.
  */
+static void uvc_video_decode_meta(struct uvc_streaming *stream,
+			struct uvc_buffer *buf, struct uvc_buffer *meta_buf,
+			u8 *mem, int length)
+{
+	size_t nbytes;
+
+	if (!meta_buf || !length)
+		return;
+
+	nbytes = min_t(unsigned int, length, meta_buf->length);
+
+	meta_buf->buf.sequence = buf->buf.sequence;
+	meta_buf->buf.field = buf->buf.field;
+	meta_buf->buf.vb2_buf.timestamp = buf->buf.vb2_buf.timestamp;
+
+	memcpy(meta_buf->mem, mem, nbytes);
+	meta_buf->bytesused = nbytes;
+	meta_buf->state = UVC_BUF_STATE_READY;
+
+	uvc_queue_next_buffer(&stream->meta.queue, meta_buf);
+}
+
 static void uvc_video_decode_isoc(struct urb *urb, struct uvc_streaming *stream,
-	struct uvc_buffer *buf)
+			struct uvc_buffer *buf, struct uvc_buffer *meta_buf)
 {
 	u8 *mem;
 	int ret, i;
@@ -1189,6 +1211,8 @@  static void uvc_video_decode_isoc(struct urb *urb, struct uvc_streaming *stream,
 		if (ret < 0)
 			continue;
 
+		uvc_video_decode_meta(stream, buf, meta_buf, mem, ret);
+
 		/* Decode the payload data. */
 		uvc_video_decode_data(stream, buf, mem + ret,
 			urb->iso_frame_desc[i].actual_length - ret);
@@ -1205,7 +1229,7 @@  static void uvc_video_decode_isoc(struct urb *urb, struct uvc_streaming *stream,
 }
 
 static void uvc_video_decode_bulk(struct urb *urb, struct uvc_streaming *stream,
-	struct uvc_buffer *buf)
+			struct uvc_buffer *buf, struct uvc_buffer *meta_buf)
 {
 	u8 *mem;
 	int len, ret;
@@ -1239,6 +1263,8 @@  static void uvc_video_decode_bulk(struct urb *urb, struct uvc_streaming *stream,
 			memcpy(stream->bulk.header, mem, ret);
 			stream->bulk.header_size = ret;
 
+			uvc_video_decode_meta(stream, buf, meta_buf, mem, ret);
+
 			mem += ret;
 			len -= ret;
 		}
@@ -1262,8 +1288,7 @@  static void uvc_video_decode_bulk(struct urb *urb, struct uvc_streaming *stream,
 			uvc_video_decode_end(stream, buf, stream->bulk.header,
 				stream->bulk.payload_size);
 			if (buf->state == UVC_BUF_STATE_READY)
-				buf = uvc_queue_next_buffer(&stream->queue,
-							    buf);
+				uvc_queue_next_buffer(&stream->queue, buf);
 		}
 
 		stream->bulk.header_size = 0;
@@ -1273,7 +1298,7 @@  static void uvc_video_decode_bulk(struct urb *urb, struct uvc_streaming *stream,
 }
 
 static void uvc_video_encode_bulk(struct urb *urb, struct uvc_streaming *stream,
-	struct uvc_buffer *buf)
+	struct uvc_buffer *buf, struct uvc_buffer *meta_buf)
 {
 	u8 *mem = urb->transfer_buffer;
 	int len = stream->urb_size, ret;
@@ -1319,7 +1344,8 @@  static void uvc_video_complete(struct urb *urb)
 {
 	struct uvc_streaming *stream = urb->context;
 	struct uvc_video_queue *queue = &stream->queue;
-	struct uvc_buffer *buf = NULL;
+	struct uvc_video_queue *qmeta = &stream->meta.queue;
+	struct uvc_buffer *buf = NULL, *buf_meta = NULL;
 	unsigned long flags;
 	int ret;
 
@@ -1338,6 +1364,7 @@  static void uvc_video_complete(struct urb *urb)
 	case -ECONNRESET:	/* usb_unlink_urb() called. */
 	case -ESHUTDOWN:	/* The endpoint is being disabled. */
 		uvc_queue_cancel(queue, urb->status == -ESHUTDOWN);
+		uvc_queue_cancel(qmeta, urb->status == -ESHUTDOWN);
 		return;
 	}
 
@@ -1347,7 +1374,13 @@  static void uvc_video_complete(struct urb *urb)
 				       queue);
 	spin_unlock_irqrestore(&queue->irqlock, flags);
 
-	stream->decode(urb, stream, buf);
+	spin_lock_irqsave(&qmeta->irqlock, flags);
+	if (!list_empty(&qmeta->irqqueue))
+		buf_meta = list_first_entry(&qmeta->irqqueue, struct uvc_buffer,
+					    queue);
+	spin_unlock_irqrestore(&qmeta->irqlock, flags);
+
+	stream->decode(urb, stream, buf, buf_meta);
 
 	if ((ret = usb_submit_urb(urb, GFP_ATOMIC)) < 0) {
 		uvc_printk(KERN_ERR, "Failed to resubmit video URB (%d).\n",
diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
index 3d6cc62..ebff4b6 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -464,6 +464,11 @@  struct uvc_stats_stream {
 	unsigned int max_sof;		/* Maximum STC.SOF value */
 };
 
+struct uvc_meta_dev {
+	struct video_device vdev;
+	struct uvc_video_queue queue;
+};
+
 struct uvc_streaming {
 	struct list_head list;
 	struct uvc_device *dev;
@@ -495,7 +500,9 @@  struct uvc_streaming {
 	unsigned int frozen : 1;
 	struct uvc_video_queue queue;
 	void (*decode) (struct urb *urb, struct uvc_streaming *video,
-			struct uvc_buffer *buf);
+			struct uvc_buffer *buf, struct uvc_buffer *meta_buf);
+
+	struct uvc_meta_dev meta;
 
 	/* Context data used by the bulk completion handler. */
 	struct {
@@ -700,6 +707,7 @@  extern int uvc_query_ctrl(struct uvc_device *dev, __u8 query, __u8 unit,
 void uvc_video_clock_update(struct uvc_streaming *stream,
 			    struct vb2_v4l2_buffer *vbuf,
 			    struct uvc_buffer *buf);
+int uvc_meta_register(struct uvc_streaming *stream);
 
 /* Status */
 extern int uvc_status_init(struct uvc_device *dev);
@@ -754,7 +762,7 @@  extern struct usb_host_endpoint *uvc_find_endpoint(
 
 /* Quirks support */
 void uvc_video_decode_isight(struct urb *urb, struct uvc_streaming *stream,
-		struct uvc_buffer *buf);
+		struct uvc_buffer *buf, struct uvc_buffer *meta_buf);
 
 /* debugfs and statistics */
 int uvc_debugfs_init(void);
diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
index 44a29af..1618be4 100644
--- a/drivers/media/v4l2-core/v4l2-ioctl.c
+++ b/drivers/media/v4l2-core/v4l2-ioctl.c
@@ -1232,6 +1232,7 @@  static void v4l_fill_fmtdesc(struct v4l2_fmtdesc *fmt)
 	case V4L2_TCH_FMT_DELTA_TD08:	descr = "8-bit signed deltas"; break;
 	case V4L2_TCH_FMT_TU16:		descr = "16-bit unsigned touch data"; break;
 	case V4L2_TCH_FMT_TU08:		descr = "8-bit unsigned touch data"; break;
+	case V4L2_META_FMT_UVC:		descr = "UVC payload header metadata"; break;
 
 	default:
 		/* Compressed formats */
diff --git a/include/uapi/linux/uvcvideo.h b/include/uapi/linux/uvcvideo.h
index 3b08186..e98de14 100644
--- a/include/uapi/linux/uvcvideo.h
+++ b/include/uapi/linux/uvcvideo.h
@@ -67,4 +67,14 @@  struct uvc_xu_control_query {
 #define UVCIOC_CTRL_MAP		_IOWR('u', 0x20, struct uvc_xu_control_mapping)
 #define UVCIOC_CTRL_QUERY	_IOWR('u', 0x21, struct uvc_xu_control_query)
 
+/*
+ * Metadata node
+ */
+
+/*
+ * Actually 255 bytes, but 256 is just a nicer number. We keep the buffer size
+ * constant and just set .usedbytes accordingly
+ */
+#define UVC_PAYLOAD_HEADER_MAX_SIZE 256
+
 #endif
diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index 1b894db..6b74191 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -678,6 +678,9 @@  struct v4l2_pix_format {
 #define V4L2_TCH_FMT_TU16	v4l2_fourcc('T', 'U', '1', '6') /* 16-bit unsigned touch data */
 #define V4L2_TCH_FMT_TU08	v4l2_fourcc('T', 'U', '0', '8') /* 8-bit unsigned touch data */
 
+/* Meta-data formats */
+#define V4L2_META_FMT_UVC         v4l2_fourcc('U', 'V', 'C', 'H') /* UVC Payload Header metadata */
+
 /* priv field value to indicates that subsequent fields are valid. */
 #define V4L2_PIX_FMT_PRIV_MAGIC		0xfeedcafe
 

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