[alsa-devel] [PATCH 0/3] alsa-lib: UCM - Use Case Manager

Jaroslav Kysela perex at perex.cz
Tue Sep 7 20:17:19 CEST 2010

On Tue, 7 Sep 2010, Mark Brown wrote:

> On Tue, Sep 07, 2010 at 04:42:57PM +0200, Jaroslav Kysela wrote:
>> control API. I think that it might be more "easy to understand" and
>> universal to define just sequence of commands like:
>> SectionDefaults [
>>          exec "amixer cset name='Master Playback Switch',index=2 1,1"
> ...
>> Because "amixer cset" command will be probably most used command, we can
>> eventually move the amixer code to alsa-lib to not create so much
>> processes and speed-up things.
>> It means that the ucm should not track card controls, but commands for
>> transitions.
> I don't understand the motivation here - what does this buy us?
> Looking at this from the embedded perspective I really would much rather
> see a use case manager that understands what it's doing (rather than
> essentially just running shell script).  This allows us to do things
> like specify target states (rather than having to have full sequences
> for all transitions, which is one of the things it'd be good to avoid)
> and will allow us to take advantage of any additions to the ALSA APIs
> for things like batching operations without changes to the per machine
> configurations.
> Having the facility to shell out in case some non-ALSA stuff needs to be
> done might be handy but I'd expect that for things within ALSA a tool
> like the use case manager would understand ALSA natively.
> For embedded systems, especially those like mobile phones with extensive
> use case requirements, the usability issues mostly come from the very
> large numbers of controls which is at best orthogonal to shelling out to
> amixer (or whatever) commands.

My idea is to have the most used commands working with the ALSA API 
built directly into the ucm code to not use fork/exec so much in embedded 
environments. But I can imagine that some system configurations can use 
this API to send events to another manager which can control another 
parts of the system like video, input devices, network devices and so on 
according the sound setup.

Also, the possibility to generate the alsa-lib's configuration files at 
run-time might be a nice feature for future. I take UCM like a way to 
integrate all things regarding PCM streams and mixer controls together and 
let users / system administrators / distribution makers create the 
abstract layers depending their requirements.

It's about flexibility.


Jaroslav Kysela <perex at perex.cz>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.

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