NicknDi
Posts: 61
Joined: Tue Jul 07, 2020 9:47 am

What exactly is bcm2835-isp and can it be disabled...

Sat May 01, 2021 1:15 pm

... without wreaking havoc with essential parts of the system?

I ask because I suspect it's what's causing the problems I'm still having getting a webcam working on web video chat platforms like Jitsi and Google meet. (See this thread: viewtopic.php?f=28&t=306408) The AV jack output issue is now resolved in the latest kernel release (5.10.11-v7l+), but in any case I'm continuing to use a usb sound card for audio output, which works fine. As does the microphone on the webcam I'm using (Logitech C920), until the camera itself cuts out. This either happens without any particular prompting after anything between 20 seconds and 5 minutes, or can be triggered by bringing up the AV settings in the web app and clicking on one of the drop-down menus. What happens then is that in the video options "bcm2835-isp" has replaced the webcam ("USB Device 0x46d:0x825") as the active video module (if that's what it is?), and sometimes then without any further intervention the webcam comes on and off as it and bcm2835-isp appear to slug it out for control! I understand that "snd_bcm2835" is the default built-in ALSA sound card module and can be safely disabled by editing the /boot/config.txt file, so that "snd_usb_audio" takes over as default. So my question is: can a similar operation be done on "bcm2835-isp"? (I've done a fair bit of googling, but found nothing so far that helps very much, probably due to my limited understanding of these technicalities.)

cleverca22
Posts: 6042
Joined: Sat Aug 18, 2012 2:33 pm

Re: What exactly is bcm2835-isp and can it be disabled...

Sat May 01, 2021 1:58 pm

the ISP mainly deals with hw accelerated bayer conversion (raw camera image to rgb or yuv), if you disable bcm2835-isp then i expect the internal camera port will not work in certain configurations

NicknDi
Posts: 61
Joined: Tue Jul 07, 2020 9:47 am

Re: What exactly is bcm2835-isp and can it be disabled...

Sat May 01, 2021 4:01 pm

cleverca22 wrote:
Sat May 01, 2021 1:58 pm
the ISP mainly deals with hw accelerated bayer conversion (raw camera image to rgb or yuv), if you disable bcm2835-isp then i expect the internal camera port will not work in certain configurations
Thank you. So my next question is: How to disable it?

6by9
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Re: What exactly is bcm2835-isp and can it be disabled...

Sat May 01, 2021 8:47 pm

It's used by libcamera.
Because V4L2 only allows a single input and/or output queue per device, in order to deliver 3 output streams it has to create 4 nodes (1 in and 3 out), hence /dev/video13-16.

Chromium can get confused as it sees /dev/video14 as a source of images so incorrectly guesses it is a webcam.

If it's really causing you grief (and it sounds more like your webcam is disconnecting rather than anything else), then you can blacklist the kernel module by creating a file called something like "bcm2835-isp.conf" in /etc/modprobe.d, with the contents "blacklist bcm2835-isp"
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NicknDi
Posts: 61
Joined: Tue Jul 07, 2020 9:47 am

Re: What exactly is bcm2835-isp and can it be disabled...

Sun May 02, 2021 8:55 pm

6by9 wrote:
Sat May 01, 2021 8:47 pm
It's used by libcamera.
Because V4L2 only allows a single input and/or output queue per device, in order to deliver 3 output streams it has to create 4 nodes (1 in and 3 out), hence /dev/video13-16.

Chromium can get confused as it sees /dev/video14 as a source of images so incorrectly guesses it is a webcam.

If it's really causing you grief (and it sounds more like your webcam is disconnecting rather than anything else), then you can blacklist the kernel module by creating a file called something like "bcm2835-isp.conf" in /etc/modprobe.d, with the contents "blacklist bcm2835-isp"
Thank you. You are right, disabling it made matters worse: "camera muted by system"!

It turns out it was the webcam all along and it's now not showing any picture at all. Light comes on, but no video. Confirmed on another computer (manjaro desktop). Grrrr! In the early stages I was always testing with more than one webcam, but once I got a working setup (for a few weeks, before an update broke it) and knew for sure that camera worked with the RPi4, I stopped using an alternative.

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