Hi Daniel,

On 11/14/18 9:35 AM, Daniel Baluta wrote:

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.

I don't think we planned for the case you mention, but IIRC it was intentional.

In our implementations and the non-Intel ones I am familiar with, the BE typically handles data that is mixed between PCM channels (for tone/alerts/low latency) and decompressed data. So the rate adaptation of the decoder output is handled inside the DSP and the BE is configured at a set rate. I also don't remember when was the last time we supported 44.1 kHz, maybe 2011?

You *could* add support for dynamic BE reconfigurations but then it creates a headache for the mixer usages. Not to mention that decoders support rates that the BE may not support so SRC is likely required anyways. And I forget schemes like AAC+ implicit signaling where you first have to decode before figuring out if you have valid SBR data which will result in a 2x upsampling of the output - in other words you may not necessarily know what the output frequency of the decoder is just by looking up the file so doing a configuration at the DPCM level is complicated at best.

-Pierre