More Generic Audio Graph Sound Card idea

[Pierre-Louis Bossart]

Hi Morimoto-san,

 > I know Pierre-Louis want to use it for SOF, but something is missing,
 > thus, can't use (?).

Here's a bit more background.

For SoundWire, we could have the following examples for amplifier 
connections, where in some cases we have two amplifiers located on 
separate links (top diagram) and in the second they are on the same link.

| FE PCMs    |  SoC DSP  | BE DAIs   | Audio devices |

              *************
   PCM0 <---> *           * DAI0 <---> Codec Headset
              *           *
   PCM1 <---> *           * DAI1 <---> Amp Left
              *   DSP     *
   PCM2 <---> *           * DAI2 <---> Amp Right
              *           *
   PCM3 <---> *           * DAI3 <---> BT
              *           *
              *           * DAI4 <---> DMIC
              *           *
              *           * DAI5 <---> FM
              *************

              *************
   PCM0 <---> *           * DAI0 <---> Codec Headset
              *           *
   PCM1 <---> *           * DAI1 <---> Amp Left
              *   DSP     *        |
   PCM2 <---> *           * DAI2/  --> Amp Right
              *           *
   PCM3 <---> *           * DAI3 <---> BT
              *           *
              *           * DAI4 <---> DMIC
              *           *
              *           * DAI5 <---> FM
              *************

We'd need a means to express that the two amplifiers are really supposed 
to operate concurrently and be synchronized, and let the drivers know 
which configuration to use (multi-cpu/multi-codec or single 
CPU/multi-codec).

Currently we do this manually by hard-coding an 'endpoint group', see 
e.g. 
https://elixir.bootlin.com/linux/latest/source/sound/soc/intel/common/soc-acpi-intel-cml-match.c#L69, 
and use this information in the machine driver to know which of the 
configurations to use.

At some point we'd like to read this information from platform firmware 
(will be ACPI for Intel but that's a detail) and create the dais in the 
right way by grouping endpoints on the same dailink when they are 
connected, and create separate dailink otherwise.

Note that we only want the connection between BEs and audio devices to 
be described in platform firmware, the topology inside the SOC DSP is 
handled with a topology file that can be changed at will to e.g. 
add/remove processing.

We really need to make sure the audio graph can be described in two 
parts, the bottom part related to hardware routing and layout, and the 
DSP part. Of course the topology part would have to be constrained to 
use the DAIs used in the lower level.

Hope this helps explain what I am looking for.

Thank you for starting this thread!

Regards

-Pierre