[Sound-open-firmware] mixer and formats question

[Pierre-Louis Bossart]

> Yes. Mixer only mixes same format today, however the PCM converter can
> be invoked here on the pipeline (but I dont think the mixer does this
> today).
> 
>> b) if yes, how is the format for a mixer defined? We typically
>> convert
>> using volume elements, but somehow a mixer would need to be set-up
>> with
>> a predefined format (i.e. not propagated by hw_params()) if we want
>> the
>> volume elements to know when/what to convert. I see in my
>> experiments
>> that the format for the mixer sources and sinks seems to be changed
>> dynamically, which doesn't seem quite right to me.
>>
> 
> It could be the PCM converter being invoked by host or dai component
> depending on which PCM is opened in which order etc ?.

Yes, the volume can convert, but the question is to what?

take a topology like this

PCM1 (S32_LE) -> volume1----v
                             --- mixer (S??) -- volume -- DAI (S16_LE)
PCM2 (S16_LE) -> volume2 -- ^

currently we only set the formats for the PCM devices and the DAIs.
It's my understanding that the format used by the mixer would be 
propagated in the hw_params stage.

That's really bad! This would mean the mixer format would be different 
depending on which of PCM1 or PCM2 is used first.

I think if we want a consistent result we *have* to define the format 
used by the mixer with e.g. a token passed to firmware with the config IPC.

A mux is probably similar btw.