Re: [PATCH 3/3] ALSA: usb-audio: Do not expose sticky mixers

[Michal Pecio <michal.pecio@gmail.com>]

On Sat, 11 Apr 2026 01:49:04 +0800, Rong Zhang wrote:
> Some devices' mixers are sticky, which accept SET_CUR but do absolutely
> nothing. Registering these mixers confuses userspace and results in
> ineffective volume control.
> 
> Check if a mixer is sticky by setting the volume to the maximum or
> minimum value and checking for effectiveness afterward. Prevent the
> mixer from being registered if it turns out to be sticky.
> 
> Quirky device sample:
> 
>   usb 7-1: New USB device found, idVendor=0e0b, idProduct=fa01, bcdDevice= 1.00
>   usb 7-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
>   usb 7-1: Product: Feaulle Rainbow
>   usb 7-1: Manufacturer: Generic
>   usb 7-1: SerialNumber: 20210726905926
>   (Mic Capture Volume)
> 
> Signed-off-by: Rong Zhang <i@rong.moe>

This appears to break (yet another) device, as reported below.
Not 100% sure because both affected users ran away to -lts and
appear to be of the "won't compile kernel patches" variety.

https://bbs.archlinux.org/viewtopic.php?id=314220

My $.02 - was there no way to deal with this in userspace,
or to make it opt-in rather than opt-out?

Regards,
Michal