[alsa-devel] Exposing the ThinkPad HW mute switch to ALSA?

[Grant Diffey]

so I have a really dumb question.

Why can't the controls be mapped as HCI rather than a soundcard? given
there's no audio production capability here only a control capability.

Also this seems to be how they end up functioning on a modern system they
get bound to pulse which remaps them to whatever's 'active'

Why does everyone say that this is a soundcard when it's really a keyboard
(from my pov)

also what's the least surprise here?

Should this control control volume of my BT headset when it's active (It
currently does which I find convenient but I can see an argument that it's
surprising and should be bound to the phys hardware on the laptop)

On Tue, Oct 7, 2014 at 4:25 PM, Takashi Iwai <tiwai at suse.de> wrote:

> At Mon, 6 Oct 2014 17:06:19 -0700,
> Andy Lutomirski wrote:
> >
> > On Mon, Oct 6, 2014 at 12:09 PM, Henrique de Moraes Holschuh
> > <hmh at hmh.eng.br> wrote:
> > > On Mon, 06 Oct 2014, Takashi Iwai wrote:
> > >> > ThinkPads have an extra mute switch that's controlled by the
> embedded
> > >> > controller.  There are some hardware buttons associated with it.
> > >> >
> > >> > We (thinkpad-acpi) can be notified about state changes in the mute
> > >> > switch, we can see presses of the hardware buttons and program them
> to
> > >> > send KEY_MUTE or not as appropriate, and we can (optionally) change
> > >> > the HW mute state.
> > >> >
> > >> > However, I have no clue how to correctly expose the mute switch
> > >> > through ALSA so that userspace will know what it controls.  It
> > >> > currently shows up as its own sound card, which is ridiculous.
> > >> >
> > >> > Can anyone give me any hints as to how to expose this bonus audio
> > >> > control in a sensible manner?  I know essentially nothing about
> ALSA.
> > >> >
> > >> > (Some older ThinkPads also have a hardware volume control with
> similar
> > >> > behavior.)
> > >>
> > >> It's a bit difficult issue, since this needs the weak module
> > >> dependency.  And even worse, different sound drivers might be used for
> > >> a single thinkpad_acpi.  So, from the programming POV, the individual
> > >> sound card instance is the easiest approach.
> > >>
> > >> Though, some HD-audio codec drivers already have a weak binding of
> > >> thinkpad_acpi stuff for Mic-mute switch.  I guess we can move the
> > >> handling of the master mute switch to the sound driver as well.
> > >>
> > >> If doing so, each relevant sound driver needs to implement it.
> > >> IIRC, snd-intel8x0 is used on old Thinkpads.  Any others?
> > >
> > > As far as I know, all old ones use the snd-intel8x0 AC97 hba, but
> several
> > > different codecs behind that.
> >
> > FWIW, I don't know whether any of the pre-hda thinkpads have the ACPI
> > HAUM/SAUM mechanism, so I have no idea how good our support for the
> > hardware mute switch and controls will ever be on those laptops.
>
> IIRC, they have, and the mute worked completely independently from the
> onboard sound controller.  But my memory is pretty vague.
>
>
> Takashi
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