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

[Andy Lutomirski]

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.

--Andy

>
> --
>   "One disk to rule them all, One disk to find them. One disk to bring
>   them all and in the darkness grind them. In the Land of Redmond
>   where the shadows lie." -- The Silicon Valley Tarot
>   Henrique Holschuh



-- 
Andy Lutomirski
AMA Capital Management, LLC