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

[seifert at oern.de]

Hi,

I have the same laptop.
I cannot test it right now and never looked at the logs, but often the 
image stays pitch black even when the webcams hardware light is active. 
What works for me is if I flash a bright light (phones flashlight) at 
the camera right after I activate it (e.g. in Zoom), it turns on.

Greetings
Björn


On 3/8/21 11:42 AM, riveravaldez via arch-general wrote:
> 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
>