Re: Adding a alsa mixer interface to ibm-acpi

[Takashi Iwai <tiwai@suse.de>]

At Sat, 24 Feb 2007 23:20:17 -0200,
Henrique de Moraes Holschuh wrote:
> 
> Hello,
> 
> I am the current maintainer of the ibm-acpi driver for the Linux kernel.
> Those of you that own a ThinkPad notebook probably know what I am talking
> about.
> 
> A ThinkPad notebook has a hardware mixer for volume control (two functions:
> volume and mute).  The user can interact with this volume control using
> three buttons (up/down/mute), and it is completely implemented in firmware.
> 
> ibm-acpi currently exports those controls through a procfs interface, but I
> am trying to get rid of it, and instead of just porting the interface to
> sysfs attributes, I tried to write a proof-of-concept alsa mixer -- if it is
> a mixer, it should be exported as one, not as some driver-specific sysfs
> attributes, IMHO :-)
> 
> It worked almost perfectly, and it was easy to write.  Many thanks to
> Takashi Iwai for his excellent docs at
> http://www.alsa-project.org/~iwai/writing-an-alsa-driver/index.html.
> 
> The only issue was in userspace, apparently alsamixer ignores VOLATILE
> controls and doesn't poll them for updates.  I wonder how widespread such
> misbehaviour is?  I may have to write an in-driver polling thread so that I
> can send notifications, if it is too widespread.

That's exactly the role of VOLATILE flag.  It's for controls with
frequently changing elements (e.g. VU-meters) and thus not suitable
for poll/select by a mixer app.  I think the case of volume buttons is
OK to use normal controls without VOLATILE flag.

> Anyway, the driver is *not* a stand-alone module, but rather just a small
> part of ibm-acpi.  I suppose I could break it into two modules so that the
> alsa mixer has its own module, but either it would *have* to depend on
> ibm-acpi, or it would have to duplicate a lot of thinkpad specific stuff.
> 
> How do you guys feel about an in-tree module that has alsa stuff in it, but
> is not part of the alsa tree?  Would that be a problem?

I'm basically for including it in ALSA driver (suppose intel8x0?) as
long as it's directly related with the sound.  If you have a working
patch, I'm willing to review and discuss more.

Anyway, the reply will be delayed since I'll be in vacation from now
for a week or so.


Thanks,

Takashi

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