Re: [PATCH v2] media: uvcvideo: Use heuristic to find stream entity

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

On Tue, Oct 21, 2025 at 06:57:00PM +0200, Ricardo Ribalda wrote:
> On Tue, 21 Oct 2025 at 18:44, Laurent Pinchart wrote:
> > On Tue, Oct 21, 2025 at 10:36:17AM +0000, Ricardo Ribalda wrote:
> > > Some devices, like the Grandstream GUV3100 webcam, have an invalid UVC
> > > descriptor where multiple entities share the same ID, this is invalid
> > > and makes it impossible to make a proper entity tree without heuristics.
> > >
> > > We have recently introduced a change in the way that we handle invalid
> > > entities that has caused a regression on broken devices.
> > >
> > > Implement a new heuristic to handle these devices properly.
> > >
> > > Reported-by: Angel4005 <ooara1337@gmail.com>
> > > Closes: https://lore.kernel.org/linux-media/CAOzBiVuS7ygUjjhCbyWg-KiNx+HFTYnqH5+GJhd6cYsNLT=DaA@mail.gmail.com/
> > > Fixes: 0e2ee70291e6 ("media: uvcvideo: Mark invalid entities with id UVC_INVALID_ENTITY_ID")
> > > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> > > ---
> > > I have managed to get my hands into a Grandstream GUV3100 and
> > > implemented a new heuristics. (Thanks Yunke and Hidenori!).
> > >
> > > With this heuristics we can use this camera again (see the /dev/video0
> > > in the topology).
> > >
> > > I have tested this change in a 6.6 kernel. Because the notebook that I
> > > used for testing has some issues running master. But for the purpose of
> > > this change this test should work.
> > >
> > > ~ # media-ctl --print-topology
> > > Media controller API version 6.6.99
> > >
> > > Media device information
> > > ------------------------
> > > driver          uvcvideo
> > > model           GRANDSTREAM GUV3100: GRANDSTREA
> > > serial
> > > bus info        usb-0000:00:14.0-9
> > > hw revision     0x409
> > > driver version  6.6.99
> > >
> > > Device topology
> > > - entity 1: GRANDSTREAM GUV3100: GRANDSTREA (1 pad, 1 link)
> > >             type Node subtype V4L flags 1
> > >             device node name /dev/video0
> > >         pad0: SINK
> > >                 <- "Extension 3":1 [ENABLED,IMMUTABLE]
> > >
> > > - entity 4: GRANDSTREAM GUV3100: GRANDSTREA (0 pad, 0 link)
> > >             type Node subtype V4L flags 0
> > >             device node name /dev/video1
> > >
> > > - entity 8: Extension 3 (2 pads, 2 links, 0 routes)
> > >             type V4L2 subdev subtype Unknown flags 0
> > >         pad0: SINK
> > >                 <- "Processing 2":1 [ENABLED,IMMUTABLE]
> > >         pad1: SOURCE
> > >                 -> "GRANDSTREAM GUV3100: GRANDSTREA":0 [ENABLED,IMMUTABLE]
> > >
> > > - entity 11: Processing 2 (2 pads, 3 links, 0 routes)
> > >              type V4L2 subdev subtype Unknown flags 0
> > >         pad0: SINK
> > >                 <- "Camera 1":0 [ENABLED,IMMUTABLE]
> > >         pad1: SOURCE
> > >                 -> "Extension 3":0 [ENABLED,IMMUTABLE]
> > >                 -> "Extension 4":0 [ENABLED,IMMUTABLE]
> > >
> > > - entity 14: Extension 4 (2 pads, 1 link, 0 routes)
> > >              type V4L2 subdev subtype Unknown flags 0
> > >         pad0: SINK
> > >                 <- "Processing 2":1 [ENABLED,IMMUTABLE]
> > >         pad1: SOURCE
> > >
> > > - entity 17: Camera 1 (1 pad, 1 link, 0 routes)
> > >              type V4L2 subdev subtype Sensor flags 0
> > >         pad0: SOURCE
> > >                 -> "Processing 2":0 [ENABLED,IMMUTABLE]
> > > ---
> > > Changes in v2:
> > > - Fix : invalid reference to the index variable of the iterator.
> > > - Link to v1: https://lore.kernel.org/r/20251021-uvc-grandstream-v1-1-801e3d08b271@chromium.org
> > > ---
> > >  drivers/media/usb/uvc/uvc_driver.c | 15 ++++++++++++++-
> > >  1 file changed, 14 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> > > index fb6afb8e84f00961f86fd8f840fba48d706d7a9a..ee4f54d6834962414979a046afc59c5036455124 100644
> > > --- a/drivers/media/usb/uvc/uvc_driver.c
> > > +++ b/drivers/media/usb/uvc/uvc_driver.c
> > > @@ -167,13 +167,26 @@ static struct uvc_entity *uvc_entity_by_reference(struct uvc_device *dev,
> > >
> > >  static struct uvc_streaming *uvc_stream_by_id(struct uvc_device *dev, int id)
> > >  {
> > > -     struct uvc_streaming *stream;
> > > +     struct uvc_streaming *stream, *last_stream;
> > > +     unsigned int count = 0;
> > >
> > >       list_for_each_entry(stream, &dev->streams, list) {
> > > +             count += 1;
> > > +             last_stream = stream;
> > >               if (stream->header.bTerminalLink == id)
> > >                       return stream;
> > >       }
> > >
> > > +     /*
> > > +      * If the streaming entity is referenced by an invalid ID, notify the
> > > +      * user and use heuristics to guess the correct entity.
> > > +      */
> > > +     if (count == 1 && id == UVC_INVALID_ENTITY_ID) {
> > > +             dev_warn(&dev->intf->dev,
> > > +                      "UVC non compliance: Invalid USB header. The streaming entity has an invalid ID, guessing the correct one.");
> > > +             return last_stream;
> > > +     }
> >
> > As far as I understand, the reason why we can't find the streaming
> > interface here is because we have set the streaming output terminal ID
> > to UVC_INVALID_ENTITY_ID, due to the extension unit being previously
> > registered with the same ID. We're therefore adding a workaround on top
> > of another workaround.
> >
> > Looking at the UVC descriptors for this camera, ID 4 is shared between
> > an extension unit with GUID ffe52d21-8030-4e2c-82d9-f587d00540bd and the
> > streaming output terminal. That GUID is apparently a Logitech GUID
> > (according to https://github.com/soyersoyer/cameractrls/blob/c920e/cameractrls.py).
> > I don't know if the XU actually works in that camera, but it could be
> > useful to keep it functional.
> >
> > I think we could make the handling of non-unique IDs more clever. If an
> > output streaming terminal and a unit share the same ID, we could
> > allocate an unused ID for the output streaming terminal, and patch the
> > bTerminalLink of the stream headers accordingly. The ID remapping should
> > not cause other issues, as
> >
> > - streaming output terminals have no controls, so the ID isn't used to
> >   reference controls
> >
> > - the units graph is build from sink to source, with UVC descriptors
> >   containing the IDs of source units, so streaming output terminals are
> >   never referenced by ID from descriptors except for the bTerminalLink.
> >
> > This would produce a valid graph without duplicated IDs in this case.
> 
> I will try to work on a solution like you propose in this kernel
> cycle, but I do not feel very confident about landing that big change
> in "fixes" without being in linux-next for a couple of weeks. I'd
> rather go for a simple solution that fixes the regression.
> 
> With this fix, the media controller topology looks identical as before
> we introduce the bug, so we do not lose any functionality.
> 
> So if you agree I think the safest path is to land this fix in fixes
> now. And try to get a better logic landed in next in this kernel
> cycle.
> 
> What do you think?

I'm fine with that timelie. Thanks for agreeing to try and implement the
above proposal.

> > > +
> > >       return NULL;
> > >  }
> > >
> > >
> > > ---
> > > base-commit: ea299a2164262ff787c9d33f46049acccd120672
> > > change-id: 20251021-uvc-grandstream-05ecf0288f62

-- 
Regards,

Laurent Pinchart