[alsa-devel] [RFC] Channel mapping API (take 2)

Takashi Iwai tiwai at suse.de
Wed Sep 5 12:34:18 CEST 2012

At Wed, 05 Sep 2012 10:32:24 +0200,
David Henningsson wrote:
> On 09/04/2012 05:47 PM, Takashi Iwai wrote:
> >    The phase inverted channel has this bit:
> >    #define SNDRV_CHMAP_PHASE_INVERSE	(0x01 << 16)
> Hmm. On second thought, as mics are plugged in and unplugged during 
> recording, the channel map will change. (E g, changing a digital mic 
> with phase inverse, to a stereo line in)
> Will we also need a notify callback in alsa-lib to know changes in the 
> channel map?

It's possible to implement (just a call of snd_ctl_notify()), but I
don't know whether this is expected by the user-space.

Obviously the configuration isn't expected to be changed dynamically
without hw_params change.  So basically ditto for the channel map.

I guess the phase inverse thing makes sense once after we implement
separate PCM streams for d-mic.  Other than that, dynamic switching
the channel map doesn't sound like a helpful scenario.


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