[arch-general] Laptop's webcam gets blocked randomly

[riveravaldez]

Hi, I'm having kind of a random webcam unavailability on a Dell XPS
L502X (Sandy Bridge) with webcam:

```
$ lsusb
Bus 001 Device 003: ID 0408:2fb1 Quanta Computer, Inc.
Laptop_Integrated_Webcam_2HDM
```

I already checked [1] but couldn't find no hint in how to diagnose this.

Sometimes webcam works fine. There's sort of a permanent static-noise
with MJPG format in qv4l2 no matter which frame size I use (sometimes
it even crash), and with guvcview using MJPG makes the image unstable
if I activate the 'mirror' filter; rest of the time I get a lot of:

```
V4L2_CORE: Error - Couldn't decode frame
V4L2_CORE: (jpeg decoder) error while decoding frame
V4L2_CORE: (jpeg decoder) error while decoding frame
V4L2_CORE: (jpeg decoder) Ignoring empty buffer
```

But using YUYV in guvcview, thou slower, the video seems OK (in qv4l2
it starts with a green screen and then the proper image appears). In
the other hand, when the webcam doesn't responds, YUYV in qv4l2 only
shows the green screen.

The hardware lights indicate that webcam is being activated, but I
have no image.

When not working, qv4l2 only says: `Hue error: connection time
expired`, I don't see any other console output.

With xawtv I get:

```
$ xawtv
This is xawtv-3.107, running on Linux/x86_64 (5.11.2-arch1-1)
xinerama 0: 1366x768+0+0
vid-open-auto: using grabber/webcam device /dev/video0
v4l2: oops: select timeout
```

And with guvcview (YUYV) I have:

```
$ guvcview
GUVCVIEW: version 2.0.6
V4L2_CORE: (UVCIOC_CTRL_MAP) Error: The file or directory does not exist
...
ALSA lib pcm.c:2660:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear
ALSA lib pcm.c:2660:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2660:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side
ALSA lib pcm_route.c:877:(find_matching_chmap) Found no matching channel map
...
connect(2) call to /dev/shm/jack-1000/default/jack_0 failed (err=The
file or directory does not exist)
attempt to connect to server failed
...
ALSA lib pcm_oss.c:377:(_snd_pcm_oss_open) Unknown field port
...
ALSA lib pcm_usb_stream.c:486:(_snd_pcm_usb_stream_open) Invalid type for card
...
V4L2_CORE: Could not grab image (select timeout): Resource temporarily
unavailable
...
```

The only related message I found on `sudo dmesg` says:

```
[33511.458233] uvcvideo: Failed to query (GET_CUR) UVC control 6 on
unit 2: -110 (exp. 2).
```

`sudo journalctl -ex` doesn't seems to show nothing about.

System is updated.

Any idea on how to pinpoint/diagnose the source of this issue?

Thanks a lot in advance!

[1] https://wiki.archlinux.org/index.php/Webcam_setup