Re: [regression] Bug 216818 - The microphone mute led not working after linux 6

[Hans de Goede]

Hi,

On 12/19/22 10:17, Thorsten Leemhuis wrote:
> Hi, this is your Linux kernel regression tracker speaking.
> 
> I noticed a regression report in bugzilla.kernel.org. As many (most?)
> kernel developer don't keep an eye on it, I decided to forward it by
> mail. Quoting from https://bugzilla.kernel.org/show_bug.cgi?id=216818 :
> 
>>  sonic82003@xxxxxxxxx 2022-12-18 08:52:32 UTC
>>
>> The mic mute led of my ThinkPad X1 Carbon Gen 9 doesn't work anymore after updating linux to version 6.
>> I can still turn it on by  running 
>>
>> echo 1 > /sys/class/leds/platform::micmute/brightness
>>
>> With linux-lts it still works fine.
> 
> See the ticket for more details.
> 
> Note, I found a similar report that (despite my attempts to prevent
> things like this from happening) fell through the cracks here:
> https://bugzilla.kernel.org/show_bug.cgi?id=216355
> 
>>  plum 2022-08-13 02:11:01 UTC
>>
>> I upgrade to kernel 5.19.1 but found my thinkpad x1 carbon 2021's mute led stop working.
>>
>> Function is okay but LED won't light up.
>>
>> Back to kernel 5.18 and it's normal and working again.
>>
>> Fedora 36 64 bit 
>> Gnome-shell 42
> 
> From a quick research it looks to me like this is an issue for the
> sounds maintainers, as the LED itself apparently works. If that is
> something for the platform people instead please speak up.

Thanks for bringing this up, we recently hit this in Fedora too
and we have a fix/workaround there. Let me copy and paste what
I just added to bko216355 :

This is caused by a behavior change of the kernel code controlling the LED to only turn on the LED when all inputs, including e.g. the jack mic input are turned off in the alsa-mixer settings.

But most userspace code only turns the mic which it is actually using on/off when you hit the mic-mute hotkey.

Also see: https://bugzilla.redhat.com/show_bug.cgi?id=2134824

Which is the same bug.

There is a set of fixes available in the form of an alsa-ucm update which tells the kernel to ignore the state of the jack mic input restoring the old behavior:

https://git.alsa-project.org/?p=alsa-ucm-conf.git;a=commitdiff;h=79a8ec44d3dcf097f4a4492c506cbcf338324175
https://git.alsa-project.org/?p=alsa-ucm-conf.git;a=commitdiff;h=9ce9ddb4a84fb467602b716575ea1d8f2bab0c39

Regards,

Hans