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

[Rong Zhang]

Hi Michal,

On Sat, 2026-08-08 at 22:10 +0200, Michal Pecio wrote:
> On Wed, 05 Aug 2026 22:32:00 +0800, Rong Zhang wrote:
> > On Tue, 2026-08-04 at 23:55 +0200, Michal Pecio wrote:
> > > My $.02 - was there no way to deal with this in userspace,
> > > or to make it opt-in rather than opt-out?  
> > 
> > While userspace can ignore hardware mixers via some configurations,
> > the current opt-out model is really about:
> > 
> >    When we can't distinguish between both, will the extra advantages
> >    of exposing a broken GET_CUR mixer outweigh the disadvantages of
> >    exposing a sticky one?
> > 
> > My answer is no.
> > 
> > A sticky hardware mixer breaks volume control completely. If a user
> > doesn't know how to tell the audio stack to ignore it, it will be a
> > terrible out-of-box experience.
> 
> Being able to work around it by using a different mixer control doesn't
> sound like "completely broken" to me. It seems the whole issue is that
> some mixer controls have no effect and you believe you can detect them
> by changing the control a few times and seeing if the vaule read back
> from HW changes accordingly. Of course, this also falsely catches mixer
> controls which are write-only.
> 
> I'm not familiar with UAC and ALSA mixer APIs so I don't know, but as
> the whole issue boils down to incluencing userspace mixer selection,
> is there really no way to perform the same heuristic in userspace, 
> 

snd-usb-audio always caches mixer value and tries to provide the cached
value whenever possible. As a side effect, userspace can't detect sticky
mixers using standard mixer control interfaces.

Thanks,
Rong

> move
> the quirk list there as well and let users override it with a click?
> 
> Regards,
> Michal