[alsa-devel] Channel map API patches: to be 3.7 or not to be?

[Takashi Iwai]

At Tue, 11 Sep 2012 10:22:23 +0200,
Takashi Iwai wrote:
> 
> At Tue, 11 Sep 2012 16:10:43 +0800,
> Raymond Yau wrote:
> > 
> > 2012-9-11 上午1:43 於 "Takashi Iwai" <tiwai at suse.de> 寫道：
> > >
> > > Hi,
> > >
> > > does anyone have concern if I push the current channel map API patches
> > > (in sound-unstable git tree topic/tlv-chmap branch) for linux-next,
> > > i.e. for inclusion to 3.7 kernel?
> > >
> > > I don't worry too much about the kernel API.  This can be refactored
> > > later.  But the kernel ABI must retain, so we won't change in an
> > > incompatible way any longer once after it's merged to the upstream.
> > >
> > > So, if anyone sees a flaw in the kernel ABI definition using control
> > > elements, let me know.
> > >
> > > (But note that the API can't be perfect for all generic purposes.
> > >  It's designed to be "good enough" for a big lack for multi-channel
> > >  streaming.  Of course, this doesn't discourage to use the API for any
> > >  other purposes.)
> > >
> > 
> > How about the channel map of the usb mono playback device and those sound
> > card which can pan mono to stereo speakers and headphone?
> 
> If the device specifies which speaker position the mono channel is
> for, then you can map it properly.  Unless it's really specified by
> the device, the mono stream is UNKNOWN position in general.

BTW, this reminds me of an open question:
  is it useful to add SND_CHMAP_MONO, or is it just redundant?

It's nothing but indicating a mono channel without any channel
position, so I supposed SND_CHMAP_UNKNOWN being sufficient.  OTOH,
SND_CHMAP_MONO would give a clear sign of mono streams while
SND_CHMAP_UNKNOWN could be used for any other exceptional purposes.


Takashi