[alsa-devel] [PATCH] ALSA: compress: Add DSP private metadata interface

[Pierre-Louis Bossart]

> AXD's got various features which require mode setting (e.g. for
> selecting between multi-device synchronization mechanisms that it
> supports). This would need an enum control, but I guess that this
> could be fudged with mutually exclusive switch controls for each of
> the enum values. AXD's also got numeric configuration parameters
> which it needs to be able to receive (e.g. parameters for stream
> synchronization heuristics, audio filter coefficients, etc.). Maybe a
> volume control with a domain wide enough could be used for this kind
> of configuration parameter. It's rather horrible, but might be fine
> for while the AXD driver is out of tree and there aren't more
> appropriate ALSA control types (e.g. enum and non-volume integer).
> :-/

I am not too sure I understand what you refer to as synchronization or 
multi-device synchronization mechanisms. Since you mentioned you only 
need an initial time, I wonder if this is conceptually related to the 
start_at() functionality discussed last year for PCM?

If you have a set of implementation-defined mechanisms related to 
algorithms, why not use an ALSA binary control where you define you own 
syntax and content and use the alsa control layer as a 'dumb' pipe 
between user and kernel. That's what everyone does for DSP control.