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#1 2021-04-29 21:37:36

possessedbysatan
Member
Registered: 2018-01-11
Posts: 9

Kernel-related audio issue, where to report?

Hello everyone!

It seems that I just stumbled upon something which I'm fairly sure is a kernel-related issue. Something similar was already reported in Fedora's bugzilla here, and it looks like it was fixed. It wasn't, though.

My setup is a Thinkpad laptop + Thinkpad dock. Steps to reproduce:
1. Connect USB DAC to docking station.
2. Change CPU governor to performance. I used cpupower to do this (cpupower frequency-set -g performance).
Done. Audio crackling will be present at this point.

Just to be sure that I didn't cause this in my Arch system I reproduced the above steps in a brand new Fedora 34 live USB, and even though they use pipewire I was able to reproduce the issue. Lastly, and since I'm extremely lazy to reproduce this in a brand-new pure Arch Linux I used the latest release of EndeavourOS (2021/04/21 iso) just to double-check and yeah, it's also happening there.

Here are some weird things I noticed:
- If the DAC is directly connected to a laptop port, there's no sound crackling. Everything works fine.
- This issue seems to temporarily disappear when I put the CPU under load. Literally running anything that puts CPU under stress (>99% usage or so).
- This issue seems to disappear when CPU governor is set to powersave (default one for intel CPUs I guess?). I said 'seems', because whenever turbo boost kicks in the issue will show up, albeit very quickly since the CPU won't stay in a high frequency for too long.

Docking station. It doesn't support Thunderbolt.
PC: Thinkpad T480

$pulseaudio --version
pulseaudio 14.2

$ pacman -Qi linux-zen
...
Version         : 5.11.16.zen1-1
...

Here's some dmesg output when connecting different DACs when CPU governor is set to performance:

[  +2.249663] usb 3-1.1: new high-speed USB device number 12 using xhci_hcd
[  +0.128493] usb 3-1.1: New USB device found, idVendor=152a, idProduct=8750, bcdDevice= 1.02
[  +0.000004] usb 3-1.1: New USB device strings: Mfr=1, Product=3, SerialNumber=0
[  +0.000002] usb 3-1.1: Product: D10
[  +0.000001] usb 3-1.1: Manufacturer: Topping
[  +0.069386] usb 3-1.1: 1:3 : unsupported format bits 0x100000000
... this happens whenever I connect my other DAC
[ +14.740944] usb 3-1.4.4: new high-speed USB device number 13 using xhci_hcd
[  +0.128627] usb 3-1.4.4: New USB device found, idVendor=152a, idProduct=85dd, bcdDevice= 2.06
[  +0.000004] usb 3-1.4.4: New USB device strings: Mfr=1, Product=3, SerialNumber=2
[  +0.000001] usb 3-1.4.4: Product: SMSL USB AUDIO
[  +0.000001] usb 3-1.4.4: Manufacturer: SMSL
[  +0.025652] usb 3-1.4.4: 1:3 : unsupported format bits 0x100000000

Whenever the audio issue happens there's nothing even remotely related to the issue in dmesg. There are only systemd audit messages related to NetworkManager/PAM stuff. Both pulseaudio's and pipewire's logs are useless as well since they don't seem to log anything related to the issue as well. This seems to be more related to the dock driver, maybe it's thinkpad_acpi messing things up? I don't know.

TL;DR: Audio crackling issues when CPU governor is set to performance when using Thinkpad USB dock.

Last edited by possessedbysatan (2021-04-29 21:46:01)

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#2 2021-09-29 14:18:02

petemir
Member
Registered: 2021-09-29
Posts: 1

Re: Kernel-related audio issue, where to report?

Hi! It's been a while (although not so much: https://xkcd.com/979/ smile ), but I just wanted to say that apparently it is already reported: https://bugzilla.kernel.org/show_bug.cgi?id=202455 (I am having the same problem, although with a different setup -i.e., Ubuntu 21.04).

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