[alsa-devel] How to propagate parameters from FE to BE with compressed audio interfaces

[Daniel Baluta]

Hello,

soc_compr_set_params_fe calls dpcm_be_dai_hw_params in order to setup
BE hw_params.

Is there a way to transfer parameters like for example the rate from FE
to BE?

In soc_compr_set_params_fe there is this code:

*
* Create an empty hw_params for the BE as the machine driver must
* fix this up to match DSP decoder and ASRC configuration.
* I.e. machine driver fixup for compressed BE is mandatory.
*/
memset(&fe->dpcm[fe_substream->stream].hw_params, 0,
       sizeof(struct snd_pcm_hw_params));

So, information about parameters is just ignored.

The only way we can setup hw_params for BE is via 
be_hw_params_fixup() but this function doesn't have any information
from FE.

My use case is something like this:

FE:
    - cpu: FSL SAI DAI interface
    - platform: DSP 
    - codec: dummy codec
BE:
    - cpu: dummy
    - platform: dummy
    - codec: cs42888.

codec could handle 44100Hz and 48000Hz streams, but the BE doesn't have
any way to know what is the rate cplay sets to FE.

thanks,
Daniel.