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Message-ID: <CANiDSCt=cS9_BsEvo8fEpRDfud9nob2nzgDR6CvmcFczZurG2w@mail.gmail.com>
Date: Mon, 14 Jul 2025 18:21:05 +0200
From: Ricardo Ribalda <ribalda@...omium.org>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
Guennadi Liakhovetski <guennadi.liakhovetski@...el.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Hans de Goede <hansg@...nel.org>,
linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-usb@...r.kernel.org
Subject: Re: [PATCH v8 4/5] media: uvcvideo: Introduce V4L2_META_FMT_UVC_MSXU_1_5
Hi Laurent
On Mon, 14 Jul 2025 at 17:00, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> Hi Ricardo,
>
> A bit of a stupid question, or rather a question that I wonder why I
> didn't think of before.
I believe we discussed this in the very beginning, when I just enabled
V4L2_META_FMT_D4XX for all the devices.
We thought that it could break applications. Imagine an APP that can
work with D4XX but not with other formats: if it tries to parse MSXU
format it might crash.
Regards
>
> 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@...hat.com>
> > Reviewed-by: Hans de Goede <hansg@...nel.org>
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.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
--
Ricardo Ribalda
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