rpi4: snd_bcm2835 kernel module not being loaded on newer balenaOS versions

[tmigone]

Latest balenaOS versions don't load the snd_bcm2835 driver by default. This results in the following problems:

• Audio jack not working (no driver)
• HDMI audio drivers not being picked up by the audio block

Investigating the exact balenaOS version where this broke and the solution.

Working on replicating this issue so far with no success.

[tmigone]

For future reference, affected device:

root@balena:~# cat /etc/os-release
ID="balena-os"
NAME="balenaOS"
VERSION="2.95.8"
VERSION_ID="2.95.8"
PRETTY_NAME="balenaOS 2.95.8"
MACHINE="raspberrypi4-64"
META_BALENA_VERSION="2.95.8"
BALENA_BOARD_REV="91ad4e1"
META_BALENA_REV="133b50d2"
SLUG="raspberrypi4-64"
root@balena:~# lsmod | grep snd
root@balena:~# cat /proc/asound/cards
 0 [vc4hdmi0       ]: vc4-hdmi - vc4-hdmi-0
                      vc4-hdmi-0
 1 [vc4hdmi1       ]: vc4-hdmi - vc4-hdmi-1
                      vc4-hdmi-1

[tmigone]

Seems to be related to DT Overlays. Haven't identified which balenaOS version this broke but:

• Not working --> vc4-kms-v3d
• Working --> vc4-fkms-v3d

[tmigone]

Looks like vc4-kms-vd3 does not do analog audio so we need snd_bcm2835 module to take care of it. However we also need the snd_bcm2835 to only take care of analog audio.

Solutions (maybe?):

• Move dtparam=audio=on in config.txt before dtoverlay=vc4-kms-v3d --> this ensures the snd_bcm2835 inits first and takes care of analog audio.
• Add /etc/modprobe.d/snd.conf with enable_headphones=1 and hdmi disabled

Sources:

• https://forums.raspberrypi.com/viewtopic.php?t=288234&start=325#p1783053
• https://archlinuxarm.org/forum/viewtopic.php?t=15340
• https://forum.manjaro.org/t/rpi4-a-v-jack-missing-when-using-vc4-driver-kms/50948/43?page=2

[rahul-thakoor]

@tmigone perhaps we need conf files similar to the ones here

[ViiMorales]

Sorry if this is a dumb question, but how can i reorder the entries in the conf file? Balena always reboots an reorders them alphabetically if i modify them manually. and if i add the entries via the configuration in the dashboard i wont matter the order as it always builds the file in that order.

this actually fixes my problem but only briefly as i said balena reboots and resets the config.txt