Re: [PATCH 3/3] media: uvcvideo: Allow userspace to increase the meta buffersize

[Ricardo Ribalda]

Hi Laurent

On Wed, 18 Mar 2026 at 20:22, Laurent Pinchart
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
>
> On Mon, Mar 09, 2026 at 03:01:56PM +0000, Ricardo Ribalda wrote:
> > Now we have the metadata size hardcoded to 10 KiB, this is a value that
> > works fine for bulk cameras or frames with no extra metadata. But not
> > for all usecases.
> >
> > We have seen some cameras that produce more metadata per frame. Eg:
>
> Can you tell what camera that is ?

It is a pretty standard Sunplus camera. It should be producing frames
at 30fps, but it had AutoFramerate based on exposure enabled and the
real fps was 15.
As a result of that there was twice of empty packages.

If you are really curious I can try to dig the lsusb.
>
> > Frame 1 captured (Bytes: 11154)
> > Frame 2 captured (Bytes: 11616)
> > Frame 3 captured (Bytes: 11374)
> > Frame 4 captured (Bytes: 11132)
> > Frame 5 captured (Bytes: 11594)
> > Frame 6 captured (Bytes: 11352)
> > Frame 7 captured (Bytes: 11110)
> > Frame 8 captured (Bytes: 11572)
> > Frame 9 captured (Bytes: 11308)
> >
> > When this happens, the driver (correctly) marks the metadata as ERROR.
>
> Is the maximum metadata size queryable through an XU on your devices ?

There is no metadata in this device, just timing information.

In MSXU there is a contol to set the size of the metadata. It is in
kilobytes :S and pretty much every device I've seen implements it
incorrectly.

>
> > This patch let userspace set bigger buffersize via S_FMT.
> >
> > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> > ---
> >  drivers/media/usb/uvc/uvc_metadata.c | 9 +++++++--
> >  drivers/media/usb/uvc/uvc_queue.c    | 2 +-
> >  drivers/media/usb/uvc/uvcvideo.h     | 3 ++-
> >  3 files changed, 10 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_metadata.c b/drivers/media/usb/uvc/uvc_metadata.c
> > index 0a906ae3f971..9de8aba1229e 100644
> > --- a/drivers/media/usb/uvc/uvc_metadata.c
> > +++ b/drivers/media/usb/uvc/uvc_metadata.c
> > @@ -50,7 +50,7 @@ static int uvc_meta_v4l2_get_format(struct file *file, void *priv,
> >               return -EINVAL;
> >
> >       fmt->dataformat = stream->meta.format;
> > -     fmt->buffersize = UVC_METADATA_BUF_SIZE;
> > +     fmt->buffersize = stream->meta.buffersize;
> >
> >       return 0;
> >  }
> > @@ -63,6 +63,7 @@ static int uvc_meta_v4l2_try_format(struct file *file, void *priv,
> >       struct uvc_device *dev = stream->dev;
> >       struct v4l2_meta_format *fmt = &format->fmt.meta;
> >       u32 fmeta = V4L2_META_FMT_UVC;
> > +     u32 buffersize;
> >
> >       if (format->type != vfh->vdev->queue->type)
> >               return -EINVAL;
> > @@ -74,10 +75,12 @@ static int uvc_meta_v4l2_try_format(struct file *file, void *priv,
> >               }
> >       }
> >
> > +     buffersize = max(UVC_METADATA_BUF_MIN_SIZE, fmt->buffersize);
> > +
> >       memset(fmt, 0, sizeof(*fmt));
> >
> >       fmt->dataformat = fmeta;
> > -     fmt->buffersize = UVC_METADATA_BUF_SIZE;
> > +     fmt->buffersize = buffersize;
> >
> >       return 0;
> >  }
> > @@ -103,6 +106,7 @@ static int uvc_meta_v4l2_set_format(struct file *file, void *priv,
> >               return -EBUSY;
> >
> >       stream->meta.format = fmt->dataformat;
> > +     stream->meta.buffersize = fmt->buffersize;
> >
> >       return 0;
> >  }
> > @@ -229,6 +233,7 @@ int uvc_meta_register(struct uvc_streaming *stream)
> >       struct uvc_video_queue *queue = &stream->meta.queue;
> >
> >       stream->meta.format = V4L2_META_FMT_UVC;
> > +     stream->meta.buffersize = UVC_METADATA_BUF_MIN_SIZE;
> >
> >       return uvc_register_video_device(dev, stream, queue,
> >                                        V4L2_BUF_TYPE_META_CAPTURE,
> > diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
> > index 68ed2883edb2..89206f761006 100644
> > --- a/drivers/media/usb/uvc/uvc_queue.c
> > +++ b/drivers/media/usb/uvc/uvc_queue.c
> > @@ -83,7 +83,7 @@ static int uvc_queue_setup(struct vb2_queue *vq,
> >
> >       switch (vq->type) {
> >       case V4L2_BUF_TYPE_META_CAPTURE:
> > -             size = UVC_METADATA_BUF_SIZE;
> > +             size = stream->meta.buffersize;
> >               break;
> >
> >       default:
> > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > index 9b4849fda12f..5ba698d2a23d 100644
> > --- a/drivers/media/usb/uvc/uvcvideo.h
> > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > @@ -409,7 +409,7 @@ struct uvc_stats_stream {
> >       unsigned int max_sof;           /* Maximum STC.SOF value */
> >  };
> >
> > -#define UVC_METADATA_BUF_SIZE 10240
> > +#define UVC_METADATA_BUF_MIN_SIZE 10240
>
> I wondered if we should have a max limit to avoid letting userspace
> starve system memory, but that can already be done through allocation of
> arbitrarily large image buffers anyway. We need proper memory accounting
> in V4L2.
>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
>
> >
> >  /**
> >   * struct uvc_copy_op: Context structure to schedule asynchronous memcpy
> > @@ -482,6 +482,7 @@ struct uvc_streaming {
> >       struct {
> >               struct uvc_video_queue queue;
> >               u32 format;
> > +             u32 buffersize;
> >       } meta;
> >
> >       /* Context data used by the bulk completion handler. */
> >
>
> --
> Regards,
>
> Laurent Pinchart



-- 
Ricardo Ribalda