[alsa-devel] Channel mapping

[Takashi Iwai]

At Wed, 21 Nov 2007 16:27:47 +0100 (CET),
Jaroslav Kysela wrote:
> 
> On Wed, 21 Nov 2007, Clemens Ladisch wrote:
> 
> > Takashi Iwai wrote:
> > > Yes, querying channel mapping is another missing piece with popular
> > > demand.
> > > 
> > > The implementation would be easy, I guess.  But we have to define the
> > > way to inform this from kernel to user space: whether create a new
> > > ioctl or extend the existing ones (if possible)...
> > 
> > It's just metadata that describes a PCM device, so I think we should use
> > TLV for this.
> > 
> > The existing struct snd_ctl_tlv uses a single integer to identify
> > control elements.  We could restrict control numid's to 31 bits and
> > use the upper bit to signal that this value includes device type and
> > device number in the lower bits, if we want to reuse the same TLV
> > ioctls.
> 
> We can also encode PCM device / subdevice numbers to data structure. But
> I think that best way is to extend channel_info PCM ioctl (create new 
> version and emulate old one - it should be quite easy to implement).

OK, that sounds feasible.

Do we have any other missing channel meta data?


Takashi