No sound on laptop after linux-libre 5.15

No sound on laptop after linux-libre 5.15

[Paxton Evans]

I've been encountering a strange sound issue lately, or rather, no sound
at all since  upgrading to linux-libre 5.15. The sound devices still
appear in alsamixer and Pavucontrol, but try as I might, there's just no
way to get them to play anything even though everything appears unmuted
and detected.

Rolling back to linux-libre 5.14.21 (guix
ea7233befb9570cce47e5ca71725b285a580cd22) totally fixes this issue. 

Troubleshooting sound issues on GNU/Linux is such a nightmare that I'm
hoping this list can help me, as I don't really know much about how
sound on our favorite OS really works, and don't have enough information
to file a bug. Can anyone give me pointers on where to start looking?
dmesg on 5.15.6 didn't seem to report anything strange.

I'm using a (Librebooted) MacBook 2,1 with no extra ("nonguix") channels
configured.

Thanks,
Paxton

Re: No sound on laptop after linux-libre 5.15

[Thiago Jung Bauermann]

Hello Paxton,

Em quarta-feira, 8 de dezembro de 2021, às 01:55:13 -03, Paxton Evans 
escreveu:
> Rolling back to linux-libre 5.14.21 (guix
> ea7233befb9570cce47e5ca71725b285a580cd22) totally fixes this issue.
> 
> Troubleshooting sound issues on GNU/Linux is such a nightmare that I'm
> hoping this list can help me, as I don't really know much about how
> sound on our favorite OS really works, and don't have enough information
> to file a bug. Can anyone give me pointers on where to start looking?
> dmesg on 5.15.6 didn't seem to report anything strange.

I’m not particularly familiar with the moving parts that make sound work 
either, so I’ll focus on the kernel side of things. My first idea would be 
trying to boot with the “debug” kernel command line option, which increases 
the verbosity of kernel messages. Perhaps something helpful will show up in 
dmesg that way?

If not, and if the only change in the working setup vs the non-working 
setup is the kernel version, then it’s a regression in the kernel. If you 
are willing to run the upstream Linux kernel on your machine (i.e., the 
non-libre kernel), the first step would be to run Linux v5.15.6 and see if 
sound works.

If it does, then it’s a bug in linux-libre itself and you should report the 
problem to them. If it doesn’t, it’s a bug in Linux itself and the most 
straightforward (but tedious and time-intensive) way to find the kernel 
commit that caused the bug is to use “git bisect”:

https://wiki.gentoo.org/wiki/Kernel_git-bisect

That is, assuming that you are comfortable building kernels.
You need to use v5.14 as your known-good version not v5.14.21 because your 
range should be a “straight line” in the version history, and v5.14.x 
versions branch off from mainline and thus aren’t ancestors of v5.15.x.

Also, since you’d be running random kernel commits, it’s important to be 
aware that there’s a small but non-zero risk of running a bad kernel 
version which could corrupt something on your system. E.g., not long ago 
during the v5.12 development cycle there was a filesystem corruption bug: 

https://www.phoronix.com/scan.php?page=news_item&px=Linux-5.12-Corruption-Fixed

You wouldn’t be at risk of hitting that particular bug since your range 
starts at v5.14, but it’s not inconceivable that there could be something 
bad in your range (though I’m not aware of anything). The safest way to 
address that is to run the bisect kernels in a temporary Linux installation 
on your machine, such as in a USB flash drive rather than on your main Linux 
installation.

-- 
Thanks,
Thiago

Re: No sound on laptop after linux-libre 5.15

[Leo Famulari]

On Wed, Dec 08, 2021 at 11:34:24PM -0300, Thiago Jung Bauermann wrote:
> Em quarta-feira, 8 de dezembro de 2021, às 01:55:13 -03, Paxton Evans 
> escreveu:
> > Rolling back to linux-libre 5.14.21 (guix
> > ea7233befb9570cce47e5ca71725b285a580cd22) totally fixes this issue.
> > 
> > Troubleshooting sound issues on GNU/Linux is such a nightmare that I'm
> > hoping this list can help me, as I don't really know much about how
> > sound on our favorite OS really works, and don't have enough information
> > to file a bug. Can anyone give me pointers on where to start looking?
> > dmesg on 5.15.6 didn't seem to report anything strange.

Thanks for your report. Everything Thiago said is important, and it
would also help if you told us what you had tried to do. That is, what
are you using to make sound?

My basic sound test is to use mpg123 to play an MP3 file. You can use
the --output option to choose which output to play through, to be sure.
And you can use --list-modules to see what's available.

On Guix System, we aim to make applications use Pulseaudio by default,
so you can use `mpg123 --output pulse file.mp3` to test that. You can
also use `mpg123 --output alsa file.mp3` if you'd rather test ALSA.

Unfortunately I currently cannot test sound on Guix System with
linux-libre. However, it does work for me on a computer using Guix
System with a custom kernel.

Re: No sound on laptop after linux-libre 5.15

[Paxton Evans]

On 2021-12-08 23:05, Leo Famulari wrote:
> On Wed, Dec 08, 2021 at 11:34:24PM -0300, Thiago Jung Bauermann wrote:
>> Em quarta-feira, 8 de dezembro de 2021, às 01:55:13 -03, Paxton Evans
>> escreveu:
>> > Rolling back to linux-libre 5.14.21 (guix
>> > ea7233befb9570cce47e5ca71725b285a580cd22) totally fixes this issue.
>> >
>> > Troubleshooting sound issues on GNU/Linux is such a nightmare that I'm
>> > hoping this list can help me, as I don't really know much about how
>> > sound on our favorite OS really works, and don't have enough information
>> > to file a bug. Can anyone give me pointers on where to start looking?
>> > dmesg on 5.15.6 didn't seem to report anything strange.
> 
> Thanks for your report. Everything Thiago said is important, and it
> would also help if you told us what you had tried to do. That is, what
> are you using to make sound?
> 
> My basic sound test is to use mpg123 to play an MP3 file. You can use
> the --output option to choose which output to play through, to be sure.
> And you can use --list-modules to see what's available.
> 
> On Guix System, we aim to make applications use Pulseaudio by default,
> so you can use `mpg123 --output pulse file.mp3` to test that. You can
> also use `mpg123 --output alsa file.mp3` if you'd rather test ALSA.
> 
> Unfortunately I currently cannot test sound on Guix System with
> linux-libre. However, it does work for me on a computer using Guix
> System with a custom kernel.

In case anyone finds this later, I wanted to update and say that this
was indeed a kernel bug, and fixed in Linux commit
7f6e3cbbd60044102373f5a7f86d5f4e89a99747 (included in 5.15.17 in both
vanilla and linux-libre).

-Paxton

Re: No sound on laptop after linux-libre 5.15

[Thiago Jung Bauermann]

Hello Paxton,

Paxton Evans <paxton@riseup.net> writes:

> On 2021-12-08 23:05, Leo Famulari wrote:
>> On Wed, Dec 08, 2021 at 11:34:24PM -0300, Thiago Jung Bauermann wrote:
>>> Em quarta-feira, 8 de dezembro de 2021, às 01:55:13 -03, Paxton Evans
>>> escreveu:
>>> > Rolling back to linux-libre 5.14.21 (guix
>>> > ea7233befb9570cce47e5ca71725b285a580cd22) totally fixes this issue.
>>> >
>>> > Troubleshooting sound issues on GNU/Linux is such a nightmare that I'm
>>> > hoping this list can help me, as I don't really know much about how
>>> > sound on our favorite OS really works, and don't have enough information
>>> > to file a bug. Can anyone give me pointers on where to start looking?
>>> > dmesg on 5.15.6 didn't seem to report anything strange.
>> 
>> Thanks for your report. Everything Thiago said is important, and it
>> would also help if you told us what you had tried to do. That is, what
>> are you using to make sound?
>> 
>> My basic sound test is to use mpg123 to play an MP3 file. You can use
>> the --output option to choose which output to play through, to be sure.
>> And you can use --list-modules to see what's available.
>> 
>> On Guix System, we aim to make applications use Pulseaudio by default,
>> so you can use `mpg123 --output pulse file.mp3` to test that. You can
>> also use `mpg123 --output alsa file.mp3` if you'd rather test ALSA.
>> 
>> Unfortunately I currently cannot test sound on Guix System with
>> linux-libre. However, it does work for me on a computer using Guix
>> System with a custom kernel.
>
> In case anyone finds this later, I wanted to update and say that this
> was indeed a kernel bug, and fixed in Linux commit
> 7f6e3cbbd60044102373f5a7f86d5f4e89a99747 (included in 5.15.17 in both
> vanilla and linux-libre).

Thank you for the update! It’s always nice to avoid https://xkcd.com/979/

-- 
Thanks
Thiago