[alsa-devel] [PATCH 1/4] ALSA: Added jack detection kcontrol support

Mark Brown broonie at kernel.org
Sat Jul 27 00:48:13 CEST 2013

On Fri, Jul 26, 2013 at 12:10:27PM -0700, Felipe Tonello wrote:
> On Fri, Jul 26, 2013 at 11:54 AM, Mark Brown <broonie at kernel.org> wrote:

> > This isn't ideal for multi-function jacks like headsets - it will report
> > a single boolean value for the jack regardless of what's plugged in
> > meaning userpace can't do things like figure out if a headset or
> > headphone is present.  It's probably OK for any realistic input button
> > since you're not going to get an input button without other things being
> > present.

> The KControl for Jack is boolean anyway. You can check it with "amixer
> contents". user-space can figure out based on the control name. At
> least PulseAudio does that way.

No, it can't do that for headset jacks - these will be created with a
single jack reporting multiple states, there's a state for headphone and
a state for microphone.  The system can generally distinguish between
having a headset or just plain headphones inserted and act accordingly
(for example, recording from the built in microphone on a phone when
used with normal headpones).

> > What I'd expect to happen here is that for multi function jacks we
> > create a control per function if the controls are valid.

> Do you mean based on snd_jack_types?

Yes.  If there's only one function supported the current code is fine
but for multiple functions it's going to discard useful information.
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