Module snd-bcm2835 does not setup /dev/snd as expected

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Module snd-bcm2835 does not setup /dev/snd as expected

Postby graysky » Thu Apr 14, 2016 4:58 am

Upon updating to linux-raspberrypi-4.4.7-1 on my RPi2, I can no longer run amixer which I need to do in order to set output to the 3.5mm jack from the shell. Downgrading to 4.1.21-1 fixes the problem. Any thought are welcomed.

Under 4.1.21-1:
$this->bbcode_second_pass_code('', '% amixer
Simple mixer control 'PCM',0
Capabilities: pvolume pvolume-joined pswitch pswitch-joined
Playback channels: Mono
Limits: Playback -10239 - 400
Mono: Playback 0 [96%] [0.00dB] [on]')

Under 4.4.7-1:
$this->bbcode_second_pass_code('', '% amixer
amixer: Mixer attach default error: No such file or directory')

EDIT: It seems that something perhaps related to how the snd-bcm2835 module setups up /dev/snd is to blame perhaps?

Under 4.1.21-1:
$this->bbcode_second_pass_code('', '% sudo modprobe snd-bcm2835

% ls -l /dev/snd
total 0
crw-rw---- 1 root audio 116, 0 Feb 22 09:40 controlC0
crw-rw---- 1 root audio 116, 16 Feb 22 09:40 pcmC0D0p
crw-rw---- 1 root audio 116, 17 Feb 22 09:40 pcmC0D1p
crw-rw---- 1 root audio 116, 1 Feb 22 09:40 seq
crw-rw---- 1 root audio 116, 33 Feb 22 09:40 timer
')

Under 4.4.7-1:
$this->bbcode_second_pass_code('', '% sudo modprobe snd-bcm2835
% ls -l /dev/snd
total 0
crw-rw---- 1 root audio 116, 1 Feb 22 09:40 seq
crw-rw---- 1 root audio 116, 33 Feb 22 09:40 timer
')
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Re: Module snd-bcm2835 does not setup /dev/snd as expected

Postby graysky » Thu Apr 14, 2016 8:40 pm

I found this which suggests that adding 'dtparam=audio=on' to /boot/config.txt will remedy this situation which indeed it does... why is it necessary I guess is my question after running under the 4.1.x series without it?
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Re: Module snd-bcm2835 does not setup /dev/snd as expected

Postby graysky » Thu Apr 14, 2016 10:00 pm

I updated the Arch wiki accordingly.
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Re: Module snd-bcm2835 does not setup /dev/snd as expected

Postby acrox999 » Fri Apr 15, 2016 2:49 am

Interesting discovery. That helped a lot. And it's weird that the parameter is now required after all this time.
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Re: Module snd-bcm2835 does not setup /dev/snd as expected

Postby tpfkanep » Fri Apr 15, 2016 6:28 pm

Thanks graysky. Was about to test if I still had wall-crawling powers.

I saw that the kernel update came with a msg that "config.txt was installed as config.txt.pacnew". The pacnew file only had a reference to gpu mem... maybe was an oversight from a tired package maintainer...?

Here some RPi engineer states$this->bbcode_second_pass_quote('', 'W')ith the newer kernels, audio won't work without dtparam=audio=on.
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Re: Module snd-bcm2835 does not setup /dev/snd as expected

Postby acrox999 » Sat Apr 16, 2016 1:44 am

The engineer however also stated that the line would be added automatically by the raspberrypi-sys-mods module which I believe, something that we do not have here.

Not to mention that post was made in the early February and we're only encountering this after the recent update. Perhaps we do have that module before and it stopped working or was removed from the latest kernel?
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Re: Module snd-bcm2835 does not setup /dev/snd as expected

Postby tpfkanep » Sat Apr 16, 2016 8:58 am

That is some sloppy "trying-to-look-clever" stuff from my part... :oops:

$this->bbcode_second_pass_quote('', 'T')he engineer however also stated that the line would be added automatically by the raspberrypi-sys-mods module which I believe, something that we do not have here.
I do not like the... sound of some module changing my config.txt
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