Genlocked alsa loopback problem with Wolfram wm8731 on 6.6.40

Start with the snd_aloop timer_source configuration and compare behavior between kernels 6.6.31 and 6.6.40 or later on the listed Raspberry Pi devices. Inspect the wm8731 and DMA-related logs while reproducing an application opening the ALSA loopback devices. Done means the loopback remains usable without repeated timer errors or subsequent DMA and soundcard failures.

Describe the bug

After upgrading to kernel 6.6.40 from 6.6.31 (same problem with 6.6.42), I can not use the alsa loopback devices genlocked to the Wolfram 8731 sound device.

Steps to reproduce the behaviour

Just update kernel and run an application which opens the alsa loopback devices.

Device (s)

Raspberry Pi 5, Raspberry Pi 4

System

cat /etc/rpi-issue

Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, 2acf7afcba7d11500313a7b93bb55a2aae20b2d6, stage2

vcgencmd version

2024/07/30 15:25:46
Copyright (c) 2012 Broadcom
version 790da7ef (release) (embedded)

uname -a

Linux gateway.hermes.radio 6.6.42-v8+ #1787 SMP PREEMPT Thu Jul 25 17:44:41 BST 2024 aarch64 GNU/Linux

Logs

Initial dmesh output. Nothing suspicious to me.

(...)
[ 4.826923] wm8731 1-001a: Assuming static MCLK
[ 4.826953] wm8731 1-001a: supply AVDD not found, using dummy regulator
[ 4.827050] wm8731 1-001a: supply HPVDD not found, using dummy regulator
[ 4.827074] wm8731 1-001a: supply DCVDD not found, using dummy regulator
[ 4.827101] wm8731 1-001a: supply DBVDD not found, using dummy regulator
[ 4.831445] audioinjector-stereo soc🔉 ASoC: driver name too long 'audioinjector-pi-soundcard' -> 'audioinjector-p'
[ 4.868650] audioinjector-stereo soc🔉 successfully loaded
(...)

After opening the alsa loopback, thousands per second of:
[ 242.922102] snd_aloop snd_aloop.1: snd_timer_start(0,0,0) failed with -22
[ 242.922117] snd_aloop snd_aloop.1: snd_timer_stop(0,0,0) failed with -16
[ 242.922152] snd_aloop snd_aloop.1: snd_timer_start(0,0,0) failed with -22
[ 242.922157] snd_aloop snd_aloop.1: snd_timer_stop(0,0,0) failed with -16
[ 242.922178] snd_aloop snd_aloop.1: snd_timer_start(0,0,0) failed with -22
[ 242.922182] snd_aloop snd_aloop.1: snd_timer_stop(0,0,0) failed with -16
[ 242.922203] snd_aloop snd_aloop.1: snd_timer_start(0,0,0) failed with -22
[ 242.922207] snd_aloop snd_aloop.1: snd_timer_stop(0,0,0) failed with -16

Then the soundcard itself starts to misbehave (crazy sounds heard):
[ 614.169627] dma dma2chan0: BUG: dma2chan0, IRQ with no descriptors
[ 629.590104] dma dma2chan0: BUG: dma2chan0, IRQ with no descriptors
[ 662.121953] dma dma2chan0: BUG: dma2chan0, IRQ with no descriptors
[ 675.205707] dma dma2chan0: BUG: dma2chan0, IRQ with no descriptors

snd-aloop module parameters:
options snd-aloop enable=1,1,1 index=1,2,3 timer_source=hw:0,0

Additional context

No response