[alsa-devel] [lennart at poettering.net: Status of ALSA "simple" mixer interface]

[Takashi Iwai]

At Tue, 20 Nov 2007 01:51:51 +0100,
Lennart Poettering wrote:
> 
> Hi!
> 
> A few days ago I sent the attached emails to Takashi and filed a
> couple of bugs on the ALSA BTS. Takashi suggested to post these issues
> on the ML as well, to allow public discussion. So, here we go.
> 
> The relevant bugs are:
> 
> https://bugtrack.alsa-project.org/alsa-bug/view.php?id=3570
> https://bugtrack.alsa-project.org/alsa-bug/view.php?id=3569
> https://bugtrack.alsa-project.org/alsa-bug/view.php?id=3568
> https://bugtrack.alsa-project.org/alsa-bug/view.php?id=3572
> https://bugtrack.alsa-project.org/alsa-bug/view.php?id=3571

Thanks.  Let's work on them in traditional tactics, divide and
conquer.  Here, the first one:


> /usr/include/alsa/mixer.h contains this comment:
> 
>    /* Simple (legacy) mixer elements API */
> 
> What does the "legacy" exactly mean? Shouldn't I be using it in new
> code? I am currently looking for some way I can find out which PCM
> channel for a stream on something like "surround51:0" maps to which
> mixer element. How am I supposed to implement something like this
> without stuff like the snd_mixer_selem_channel_id_t?

The "legacy" here seems to mean a legacy-style mixer elements API, not
as a deprecated API.  The abstraction is done for the playback/capture
volumes and switches and channels are re-composed to match with the
traditional channel setting.  In the earlier version, it had no enum
controls, too.

The mapping between the mixer element and the PCM element is a missing
piece, together with the PCM channel mapping.  I think we'll be able
to implement both features together.


Takashi