[alsa-devel] [PATCH 00/11] Add AXD Audio Processing IP driver

[Vinod Koul]

On Tue, Oct 28, 2014 at 10:13:48PM +0800, Greg Kroah-Hartman wrote:
> On Tue, Oct 28, 2014 at 01:18:28PM +0000, Qais Yousef wrote:
> > On 10/28/2014 11:55 AM, Clemens Ladisch wrote:
> > >Qais Yousef wrote:
> > >>AXD Audio Processing IP performs audio decoding, encoding, mixing, equalisation,
> > >>synchronisation and playback.
> > >What exactly do you mean with "synchronisation" and "playback"?
> > 
> > Synchronisation refers to accurate audio playout relative to a master
> > clock source including compensation of drift between the master clock
> > source and the playout clock of the audio hardware. Hence allowing
> > synchronised audio playout across multiple independent devices.
> > 
> > Playback simple refers to the fact that AXD is capable of managing audio
> > playout hardware like I2S and SPDIF interfaces.
> > 
> > 
> > >>It doesn't fit in alsa subsystem but I Cced them to confirm.
> > >... because those two words sound like something that a sound card could do.
> > 
> > The problem mainly stems from the fact that we take a variety of
> > compressed audio as input and we could perform audio encoding. The
> > problem with the compressed audio is that the range of decoders and
> > configuration supported in alsa is limited and there's no support for
> > taking raw pcm and producing compressed output. I'm not an expert on
> > alsa but when I looked it looked like there's more infra structure
> > required.
> > 
> > The following not supported points from Documentation/sound/alsa/compress_offload.txt affect us:
> > 
> > - Volume control/routing is not handled by this API. Devices exposing a
> >   compressed data interface will be considered as regular ALSA devices;
> >   volume changes and routing information will be provided with regular
> >   ALSA kcontrols.
> > 
> > - Embedded audio effects. Such effects should be enabled in the same
> >   manner, no matter if the input was PCM or compressed.
> > 
> > - Encoding/decoding acceleration is not supported as mentioned
> >   above. It is possible to route the output of a decoder to a capture
> >   stream, or even implement transcoding capabilities. This routing
> >   would be enabled with ALSA kcontrols.
> 
> So instead you created a one-off api just for this hardware?  Ick, no,
> please work with the audio developers to incorporate it into the
> standard Linux audio apis so that everyone can benifit and not require
> special userspace programs to drive this hardware.
I think it more a case of I want it do this by method A, ...naaaaah thats
not what is availble in ALSA so let me redo the whole stack rather than
model my driver to use ALSA

-- 
~Vinod