linux-kernel - Re: [PATCH v4 3/3] media: uvcvideo: Add a unique suffix to camera names

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Message-ID: <Y6LmJGgBYfSMBsj+@pendragon.ideasonboard.com>
Date:   Wed, 21 Dec 2022 12:55:32 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     Yunke Cao <yunkec@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        linux-media@...r.kernel.org,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/3] media: uvcvideo: Add a unique suffix to camera
 names

Hi Ricardo,

On Wed, Dec 21, 2022 at 12:00:58AM +0100, Ricardo Ribalda wrote:
> On Tue, 6 Dec 2022 at 00:02, Ricardo Ribalda wrote:
> > On Mon, 5 Dec 2022 at 23:16, Laurent Pinchart wrote:
> > > On Fri, Dec 02, 2022 at 06:08:19PM +0100, Ricardo Ribalda wrote:
> > > > Some cameras have multiple data inputs (i.e. IR sensor and RGB sensor),

Did you mean "data outputs" by the way ?

> > > > append a unique number to the device name.
> > > >
> > > > Fixes v4l2-compliance:
> > > >     Media Controller ioctls:
> > > >          fail: v4l2-test-media.cpp(205): v2_entity_names_set.find(key) != v2_entity_names_set.end()
> > > >        test MEDIA_IOC_G_TOPOLOGY: FAIL
> > > >          fail: v4l2-test-media.cpp(394): num_data_links != num_links
> > > >        test MEDIA_IOC_ENUM_ENTITIES/LINKS: FAIL
> > > >
> > > > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > > > ---
> > > >  drivers/media/usb/uvc/uvc_driver.c | 3 ++-
> > > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> > > > index 215fb483efb0..f4032ebb3689 100644
> > > > --- a/drivers/media/usb/uvc/uvc_driver.c
> > > > +++ b/drivers/media/usb/uvc/uvc_driver.c
> > > > @@ -1963,7 +1963,8 @@ int uvc_register_video_device(struct uvc_device *dev,
> > > >               break;
> > > >       }
> > > >
> > > > -     strscpy(vdev->name, dev->name, sizeof(vdev->name));
> > > > +     snprintf(vdev->name, sizeof(vdev->name), "%s %u", dev->name,
> > > > +              stream->header.bTerminalLink);
> > >
> > > This won't be perfect as the string is not guaranteed to fit in
> > > vdev->name, but I suppose it will help as a quick fix for some devices.
> > > How about the other devices ? Won't they still exhibit the above
> > > v4l2-compliance failure ? Isn't that something that will still affect
> > > Chrome OS devices ?
> >
> > We could place the id first... but that will look bad: Eg:
> >
> > 1- My favorite camera
> >
> > Another option is to remove the last chars to fit the id. Eg:
> >
> > My favorite came-1
> >
> > If you prefer any of those options or have a better idea I can implement that.
> 
> @Laurent
> 
> Any preference here?

I think the latter is better. Could we do so only when there are
multiple video capture devices (excluding the metadata device) though ?
That way we won't have a weird "-n" suffix in the majority of use cases.

> > > The change should not cause any regression as big as in patch 1/3.
> > > However, unless I'm mistaken users will notice a device name change,
> > > especially when selecting a device in their web browser. Could that be a
> > > problem ?
> >
> > I think the only side effect is that the first time that the kernel
> > changes the naming convention, if there are more than one camera on
> > the system, the video conference might pick a different camera.
> > The good news is that the user will be presented with cameras with
> > different names. Now some cameras show very confusing names:
> >
> > ribalda@...o:~/work/linux$ for a in /dev/video* ; do yavta -l $a| grep
> > "Dell Webcam"; done
> > Device `Dell Webcam WB7022' on `usb-0000:2d:00.0-1.2.3.1' (driver
> > 'uvcvideo') supports video, capture, without mplanes.
> > Device `Dell Webcam WB7022' on `usb-0000:2d:00.0-1.2.3.1' (driver
> > 'uvcvideo') supports meta-data, capture, without mplanes.
> > Device `Dell Webcam WB7022' on `usb-0000:2d:00.0-1.2.3.1' (driver
> > 'uvcvideo') supports video, capture, without mplanes.
> > Device `Dell Webcam WB7022' on `usb-0000:2d:00.0-1.2.3.1' (driver
> > 'uvcvideo') supports meta-data, capture, without mplanes.

I'm tempted to add a new model read-only string control to overcome the
length limitation. It could then be combined with other information
(such as the location and supported pixel formats) to create a
user-friendly camera name by applications.

> > > >       /*
> > > >        * Set the driver data before calling video_register_device, otherwise
> > > >

-- 
Regards,

Laurent Pinchart