Re: [PATCH] media: uvcvideo: Enable full UVC metadata for all devices

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

On Wed, Mar 05, 2025 at 02:03:58PM +0100, Hans de Goede wrote:
> On 3-Mar-25 5:22 PM, Ricardo Ribalda wrote:
> > On Mon, 3 Mar 2025 at 17:11, Laurent Pinchart wrote:
> >> On Mon, Mar 03, 2025 at 04:43:50PM +0100, Hans de Goede wrote:
> >>> On 3-Mar-25 16:13, Laurent Pinchart wrote:
> >>>> On Mon, Mar 03, 2025 at 03:47:51PM +0100, Hans de Goede wrote:
> >>>>> On 26-Feb-25 14:00, 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 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 removes the UVC_INFO_META macro and enables
> >>>>>> V4L2_META_FMT_D4XX for every device. It also updates the documentation
> >>>>>> to reflect the change.
> >>>>>>
> >>>>>> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> >>>>>
> >>>>> Thanks, patch looks good to me:
> >>>>>
> >>>>> Reviewed-by: Hans de Goede <hdegoede@redhat.com>
> >>>>
> >>>> I don't quite agree, sorry.
> >>>>
> >>>> The reason why the current mechanism has been implemented this way is to
> >>>> ensure we have documentation for the metadata format of devices that
> >>>> expose metadata to userspace.
> >>>>
> >>>> If you want to expose the MS metadata, you can create a new metadata
> >>>> format for that, and enable it on devices that implement it.
> >>>
> >>> Looking at the long list of quirks this removes just for the D4xx
> >>> cameras I do not believe that having quirked based relaying of
> >>> which metadata fmt is used to userspace is something which scales
> >>> on the long term. Given the large amount of different UVC cameras
> >>> I really think we should move the USB VID:PID -> metadata format
> >>> mapping out of the kernel.
> >>
> >> If we can find a solution to ensure the metadata format gets documented,
> >> sure.
> > 
> > MS default metadata is already documented:
> > https://learn.microsoft.com/en-us/windows-hardware/drivers/stream/mf-capture-metadata
> > 
> > I would not worry too much about vendors abusing the metadata for
> > custom magic if that is your concern.
> > This would not work with Windows default driver, and that is what most
> > camera modules are tested against.
> > 
> >> When it comes to the MS metadata format, if I recall correctly, Ricardo
> >> said there's an XU with a known GUID to detect the metadata format. We
> >> therefore wouldn't need quirks.
> > 
> > There is MXSU control 	
> > https://learn.microsoft.com/en-us/windows-hardware/drivers/stream/uvc-extensions-1-5
> > But not all the vendors use it.
> 
> Right so I actually already checked:
> 
> https://learn.microsoft.com/en-us/windows-hardware/drivers/stream/uvc-extensions-1-5
> 
> yesterday before my udev hwdb suggestion I was wondering if there was a way
> to just get if MSmetadata was used from the camera itself. What I found was this:
> 
> "UVC metadata is opt-in. Every IHV/OEM that needs metadata support must be enabled through a custom INF file."
> 
> which lead me to the udev + hwdb suggestion.
> 
> It is good to know that some cameras have a a way to fet this from a known XU GUID,
> but the official way seems to be to have per camera info in .inf files. So for Linux
> that would translate to having a list of vid:pid combinations somewhere.
> 
> The question then becomes where do we put the vid:pid list and IMHO hwdb is much
> better (easier to maintain / update) then hardcoding this in the kernel.

Additional questions: where do we store documentation for the metadata
format, how do we convey what format is supported to applications, and
how do we enable metadata capture when a device is listed in the DB ?

-- 
Regards,

Laurent Pinchart