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

[Takashi Iwai]

At Tue, 7 Oct 2014 17:43:11 -0700,
Andy Lutomirski wrote:
> 
> On Tue, Oct 7, 2014 at 7:50 AM, Takashi Iwai <tiwai at suse.de> wrote:
> > At Tue, 7 Oct 2014 07:44:35 -0700,
> > Andy Lutomirski wrote:
> >>
> >> On Oct 7, 2014 6:20 AM, "Henrique de Moraes Holschuh" <hmh at hmh.eng.br> wrote:
> >> >
> >> > On Tue, 07 Oct 2014, Takashi Iwai wrote:
> >> > > At Tue, 7 Oct 2014 17:25:13 +1100,
> >> > > Grant Diffey wrote:
> >> > > > 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)
> >> > >
> >> > > thinkpad_acpi actually mutes the sound on some models, at least the
> >> > > old ones, independently from the sound chip mute state.  That's why it
> >> > > was implemented as the sound card object initially.
> >> >
> >> > That's how the hardware works, really.  One AC97 audio channel is routed to
> >> > a digital volume chip, and from there to the console headphone jack, and to
> >> > the built-in speakers.  line-out is not routed through this chip, and AFAIK
> >> > MIC/line-in is not routed through either this chip _or_ a separate mute
> >> > gate, either.
> >> >
> >> > The EC controls this digital volume chip directly, it is independent from
> >> > the AC97 mixer.  The default behaviour cannot be changed in earlier
> >> > thinkpads, and trying to change it in later thinkpads (they're supposed to
> >> > have a legacy mode that is the same as the older models) doesn't work very
> >> > well.
> >> >
> >> > Line-out and MIC are controlled only by the AC97 mixer in the older models
> >> > with digital volume control.
> >> >
> >> > In newer-but-not-newest thinkpads, there are two mute gates, one for MIC,
> >> > and another for the speakers/headphones.  The EC controls those.  All volume
> >> > control is in the HDA mixer.
> >> >
> >> > In the newest thinkpads, I think there's only a MIC mute gate controlled by
> >> > the EC, and everything else is in the HDA mixer.
> >> >
> >> > And depeding on the EC operating mode and thinkpad model, the volume hotkeys
> >> > might interact with the mute state (unmuting on first press when it is
> >> > mute).
> >> >
> >>
> >> On newish thinkpads (at least X60-X220, and I think this works on the
> >> latest models as well), we can disable all of this and make the mute
> >> button be a regular button if we want.  Getting the mute LED to DTRT
> >> might be tricky, but modern userspace can probably do it.
> >>
> >> This is almost certainly the approach that does something sensible
> >> with the least code written.  We would just check for HAUM/SAUM on
> >> startup and, if available, set SAUM to "software control only",
> >> force-unmute the mute circuit, force the volume to full, and disable
> >> the fake soundcard.
> >
> > That sounds sensible.  But, we'll still need to handle the mute LED,
> > like we do for the mic-mute LED now?
> 
> Already done, I think:
> 
>         if (led_set_func(TPACPI_LED_MUTE, false) >= 0) {
>             old_vmaster_hook = spec->vmaster_mute.hook;
>             spec->vmaster_mute.hook = update_tpacpi_mute_led;
>             removefunc = false;
>         }

Ah, right, I forgot that we have already both mute LEDs.

> Admittedly, I see some value in having the mute button mute things
> regardless of what userspace is doing, but I don't see *much* value in
> it.  And, arguably, if that behavior is actually desirable, it should
> be available on all laptops, not just ThinkPads.

Yes.


Takashi