Re: [ibm-acpi-devel] Adding a alsa mixer interface to ibm-acpi

[Henrique de Moraes Holschuh <hmh@hmh.eng.br>]

On Wed, 07 Mar 2007, Shem Multinymous wrote:
> On 3/7/07, Takashi Iwai <tiwai@suse.de> wrote:
> > > If they got a mixer applet worth something, it will list two cards, or allow
> > > them to have two instances, one for each card.
> >
> > I guess it's rather confusing.  Both controls the very same device for
> > the very same role in the end, so it'd be better to be merged in some
> > level, IMO.
> 
> The ibm-acpi mixer also affects the BIOS-generated sounds (e.g.,
> low-battery warnings) and PC speaker. So it useful even when the sound
> card is unused or unsupported.

True.  Here's the (probable) audio routing on a ThinkPad:

[embedded sound card/codec] -> [thinkpad hardware mixer] -> output
[thinkpad firmware beep generator]   ----^

The thinkpad firmware can generate a bunch of beeps that appear to not be
really related to the std. PC buzzer :-)  and these beeps are used to signal
firmware events.  I don't think they are routed through the AC97 or HDA
codec.

Note that it is possible that the normal PC buzzer IS routed through the
codec.

One of the things I don't know is exactly what is generating the firmware
beeps on modern thinkpads: BIOS, or EC.  The volume control is done by the
EC on a modern thinkpad, though.

So I'd have to provide a stand-alone "placeholder" card to hook the mixer to
if no real sound-card driver is loaded?  urk.  It is doable, of course,
but... ick.  The question is now, what should I do when doing a mixer
piggy-back?  De-register the mixer-only audio card, or keep it around (and
this give the user two cards)?

-- 
  "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

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