Re: [PATCH v8 4/5] media: uvcvideo: Introduce V4L2_META_FMT_UVC_MSXU_1_5

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

Hi Ricardo,

A bit of a stupid question, or rather a question that I wonder why I
didn't think of before.

On Mon, Jul 07, 2025 at 06:34:04PM +0000, Ricardo Ribalda wrote:
> The UVC driver provides two metadata types V4L2_META_FMT_UVC, and
> V4L2_META_FMT_D4XX. The only difference between the two of them is that
> V4L2_META_FMT_UVC only copies PTS, SCR, size and flags, and
> V4L2_META_FMT_D4XX copies the whole metadata section.
> 
> Now we only enable V4L2_META_FMT_D4XX for the Intel D4xx family of
> devices, but it is useful to have the whole metadata payload for any
> device where vendors include other metadata, such as the one described by
> Microsoft:
> https://learn.microsoft.com/en-us/windows-hardware/drivers/stream/mf-capture-metadata
> 
> This patch introduces a new format V4L2_META_FMT_UVC_MSXU_1_5, that is
> identical to V4L2_META_FMT_D4XX.

Wouldn't it be simpler for everybody to just

#define V4L2_META_FMT_UVC_MSXU_1_5  v4l2_fourcc('D', '4', 'X', 'X') /* UVC MSXU metadata */
#define V4L2_META_FMT_D4XX	V4L2_META_FMT_UVC_MSXU_1_5 /* For backward compatibility */

? I'm a bit uncomfortable with committing to a UABI with two different
4CCs for the exact same format.

> Let the user enable this format with a quirk for now. This way they can
> test if their devices provide useful metadata without rebuilding the
> kernel. They can later contribute patches to auto-quirk their devices.
> We will also work in methods to auto-detect devices compatible with this
> new metadata format.
> 
> Suggested-by: Hans de Goede <hdegoede@redhat.com>
> Reviewed-by: Hans de Goede <hansg@kernel.org>
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> ---
>  .../userspace-api/media/v4l/meta-formats.rst       |  1 +
>  .../media/v4l/metafmt-uvc-msxu-1-5.rst             | 23 ++++++++++++++++++++++
>  MAINTAINERS                                        |  1 +
>  drivers/media/usb/uvc/uvc_metadata.c               |  4 ++++
>  drivers/media/usb/uvc/uvcvideo.h                   |  1 +
>  drivers/media/v4l2-core/v4l2-ioctl.c               |  1 +
>  include/uapi/linux/videodev2.h                     |  1 +
>  7 files changed, 32 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/meta-formats.rst b/Documentation/userspace-api/media/v4l/meta-formats.rst
> index bb6876cfc271e1a0543eee4209d6251e1a6a73cc..0de80328c36bf148051a19abe9e5241234ddfe5c 100644
> --- a/Documentation/userspace-api/media/v4l/meta-formats.rst
> +++ b/Documentation/userspace-api/media/v4l/meta-formats.rst
> @@ -20,6 +20,7 @@ These formats are used for the :ref:`metadata` interface only.
>      metafmt-pisp-fe
>      metafmt-rkisp1
>      metafmt-uvc
> +    metafmt-uvc-msxu-1-5
>      metafmt-vivid
>      metafmt-vsp1-hgo
>      metafmt-vsp1-hgt
> diff --git a/Documentation/userspace-api/media/v4l/metafmt-uvc-msxu-1-5.rst b/Documentation/userspace-api/media/v4l/metafmt-uvc-msxu-1-5.rst
> new file mode 100644
> index 0000000000000000000000000000000000000000..dd1c3076df243d770a13e7f6d07c3296a269e16a
> --- /dev/null
> +++ b/Documentation/userspace-api/media/v4l/metafmt-uvc-msxu-1-5.rst
> @@ -0,0 +1,23 @@
> +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
> +
> +.. _v4l2-meta-fmt-uvc-msxu-1-5:
> +
> +***********************************
> +V4L2_META_FMT_UVC_MSXU_1_5 ('UVCM')
> +***********************************
> +
> +Microsoft(R)'s UVC Payload Metadata.
> +
> +
> +Description
> +===========
> +
> +V4L2_META_FMT_UVC_MSXU_1_5 buffers follow the metadata buffer layout of
> +V4L2_META_FMT_UVC with the only difference that it includes all the UVC
> +metadata in the `buffer[]` field, not just the first 2-12 bytes.
> +
> +The metadata format follows the specification from Microsoft(R) [1].
> +
> +.. _1:
> +
> +[1] https://docs.microsoft.com/en-us/windows-hardware/drivers/stream/uvc-extensions-1-5
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 658543062bba3b7e600699d7271ffc89250ba7e5..fdde1d37ed2ef9058e3ea3417bec25afe454dfc0 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -25827,6 +25827,7 @@ S:	Maintained
>  W:	http://www.ideasonboard.org/uvc/
>  T:	git git://linuxtv.org/media.git
>  F:	Documentation/userspace-api/media/drivers/uvcvideo.rst
> +F:	Documentation/userspace-api/media/v4l/metafmt-uvc-msxu-1-5.rst
>  F:	Documentation/userspace-api/media/v4l/metafmt-uvc.rst
>  F:	drivers/media/common/uvc.c
>  F:	drivers/media/usb/uvc/
> diff --git a/drivers/media/usb/uvc/uvc_metadata.c b/drivers/media/usb/uvc/uvc_metadata.c
> index 4bcbc22f47e67c52baf6e133f240131ff3d32a03..77e03273d3cf6b00cac6ebb9b29b941f1cbfd9f7 100644
> --- a/drivers/media/usb/uvc/uvc_metadata.c
> +++ b/drivers/media/usb/uvc/uvc_metadata.c
> @@ -195,6 +195,10 @@ void uvc_meta_init(struct uvc_device *dev)
>  	    !WARN_ON(dev->info->meta_format == V4L2_META_FMT_UVC))
>  		dev->meta_formats[i++] = dev->info->meta_format;
>  
> +	if (dev->quirks & UVC_QUIRK_MSXU_META &&
> +	    !WARN_ON(dev->info->meta_format == V4L2_META_FMT_UVC_MSXU_1_5))
> +		dev->meta_formats[i++] = V4L2_META_FMT_UVC_MSXU_1_5;
> +
>  	 /* IMPORTANT: for new meta-formats update UVC_MAX_META_DATA_FORMATS. */
>  	dev->meta_formats[i++] = 0;
>  }
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index b3c094c6591e7a71fc00e1096bcf493a83f330ad..616adc417c62a58686beccbc440a5dfac0a2d588 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -77,6 +77,7 @@
>  #define UVC_QUIRK_DISABLE_AUTOSUSPEND	0x00008000
>  #define UVC_QUIRK_INVALID_DEVICE_SOF	0x00010000
>  #define UVC_QUIRK_MJPEG_NO_EOF		0x00020000
> +#define UVC_QUIRK_MSXU_META		0x00040000
>  
>  /* Format flags */
>  #define UVC_FMT_FLAG_COMPRESSED		0x00000001
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index be94a79b976e3de4eb957f5d2584ec6d4230469e..993b36417b4655456ce545cb42a41b55b98e4d6c 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -1463,6 +1463,7 @@ static void v4l_fill_fmtdesc(struct v4l2_fmtdesc *fmt)
>  	case V4L2_META_FMT_VSP1_HGO:	descr = "R-Car VSP1 1-D Histogram"; break;
>  	case V4L2_META_FMT_VSP1_HGT:	descr = "R-Car VSP1 2-D Histogram"; break;
>  	case V4L2_META_FMT_UVC:		descr = "UVC Payload Header Metadata"; break;
> +	case V4L2_META_FMT_UVC_MSXU_1_5:	descr = "UVC MSXU Metadata"; break;
>  	case V4L2_META_FMT_D4XX:	descr = "Intel D4xx UVC Metadata"; break;
>  	case V4L2_META_FMT_VIVID:       descr = "Vivid Metadata"; break;
>  	case V4L2_META_FMT_RK_ISP1_PARAMS:	descr = "Rockchip ISP1 3A Parameters"; break;
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 6f7bd38dd5aa4b1b2084685512512a380d76a5e4..863bc5b7dec32303e852d7e9c3891011ce5a3d71 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -867,6 +867,7 @@ struct v4l2_pix_format {
>  #define V4L2_META_FMT_VSP1_HGT    v4l2_fourcc('V', 'S', 'P', 'T') /* R-Car VSP1 2-D Histogram */
>  #define V4L2_META_FMT_UVC         v4l2_fourcc('U', 'V', 'C', 'H') /* UVC Payload Header metadata */
>  #define V4L2_META_FMT_D4XX        v4l2_fourcc('D', '4', 'X', 'X') /* D4XX Payload Header metadata */
> +#define V4L2_META_FMT_UVC_MSXU_1_5  v4l2_fourcc('U', 'V', 'C', 'M') /* UVC MSXU metadata */
>  #define V4L2_META_FMT_VIVID	  v4l2_fourcc('V', 'I', 'V', 'D') /* Vivid Metadata */
>  
>  /* Vendor specific - used for RK_ISP1 camera sub-system */

-- 
Regards,

Laurent Pinchart