[alsa-devel] UCM: Possible snd_use_case_get enhancements

[Stephen Warren]

Liam,

The recent patches I posted allow querying a modifier/device's supported/
conflicting device list from a modifier/device either within the
currently active verb (if any) or an explicitly defined verb.

I figured a similar enhancement to snd_use_case_get might be useful; i.e.
to allow querying within a specific verb, and also to indicate that one
shouldn't fall back to a verb, or overall values. I'd propose something
like this:

NAME[[=]/<modifier>|<device>[/[=]<verb>]]

The "=" would prevent fallback to a "higher" object if present. So for
example:

Current verb, not from device or modifier, with fallback to verb and
ValueDefaults:

PlaybackVolume

Current verb, from device/modifier with fallback to verb and
ValueDefaults:

PlaybackVolume/Play Music

Current verb, from dev/mod without fallback to verb or ValueDefaults:

PlaybackVolume/=Play Music

Specify a verb and dev/mod, but allow fallback to verb or ValueDefaults:

PlaybackVolume/Play Music/HiFi

Specify a verb and dev/mod, but no fallback to verb or ValueDefaults:

PlaybackVolume/=Play Music/=HiFi

One can also query from just a verb, with/without fallback:

PlaybackVolume//HiFi
PlaybackVolume//=HiFi

Or current verb with no fallback:

PlaybackVolume//=

Does this seem useful, and a sane query string syntax?

An alternative would be to drop the added "=" stuff, and never auto-
fallback. However, that'd be a regression relative to current
functionality, force clients to implement fallback themselves, and make
querying ValueDefaults hard.

-- 
nvpublic