Re: Bug: Two device nodes created in /dev for a single UVC webcam

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

Hello,

On Monday, 19 February 2018 15:58:40 EET Guennadi Liakhovetski wrote:
> On Mon, 19 Feb 2018, Kieran Bingham wrote:
> > On 17/02/18 20:47, Alexandre-Xavier Labonté-Lamoureux wrote:
> >> Hi,
> >> 
> >> I'm running Linux 4.9.0-5-amd64 on Debian. I built the drivers from
> >> the latest git and installed the modules.
> > 
> > Could you please be specific here?
> > 
> > Are you referring to linux-media/master branch or such? The latest from
> > Linus' tree?
> > 
> > Please also detail the steps you have taken to reproduce this issue - and
> > of course - if you have made any code changes to make the latest UVC
> > module compile against a v4.9 kernel...
> > 
> > Building the latest git tree and installing as a module on a v4.9 kernel
> > is quite a leap... I wouldn't have expected that to work.
> > 
> > The code would have to be compiled against a v4.9 kernel directly, and I
> > didn't think compiling the UVC driver against older kernels worked.
> > 
> > (at least it didn't work cleanly when I tried to compile v4.15 against a
> > v4.14 kernel last month)
> > 
> >> Now, two device nodes are created for my webcam. This is not normal as
> >> it has never happened to me before. If I connect another webcam to my
> >> laptop, two more device nodes will be created for this webcam. So two
> >> new device nodes are created for a single webcam.
> > 
> > I believe Guennadi's latest work for handling meta-data (in the latest
> > v4.16-rc1 I think) will create two device nodes.
> 
> That's correct. The lower index node (/dev/video0) is a video node, the
> higher videoo node (/dev/video1) is a metadata node.
> 
> > > The name of my webcam appears twice in the device comobox in Guvcview
> > > because of this. One of them will not work if I select it.
> > 
> > It would be expected that only the device with video functions as a
> > streaming camera device, while the other would not.
> 
> Exactly.
> 
> > > My webcam has completely stopped working with Cheese and VLC.
> > 
> > This part is of particular concern however.
> > 
> > Guennadi - Have you tested Cheese/VLC with your series?
> 
> Sure, with cheese you can specify which camera you need by using its
> --device= parameter. Eventually it's expected, that those programs will be
> updated to recognise metadata nodes and not attempt to use them.

I've tested VLC (2.2.8) and haven't noticed any issue. If a program is 
directed to the metadata video node and tries to capture video from it it will 
obviously fail. That being said, software that work today should continue 
working, otherwise it's a regression, and we'll have to handle that.

> > Are there any known issues that need looking at ?
> > 
> >>> v4l2-ctl --list-devices
> >> 
> >> Laptop_Integrated_Webcam_E4HD:  (usb-0000:00:1a.0-1.5):
> >>     /dev/video0
> >>     /dev/video1
> >>> 
> >>> ls /dev/video*
> >> 
> >> /dev/video0  /dev/video1

-- 
Regards,

Laurent Pinchart