[pulseaudio-discuss] alsa ucm in pulseaudio

[David Henningsson]

On 10/14/2011 11:42 AM, Feng Wei wrote:
> 2011/10/14 David Henningsson<david.henningsson at canonical.com>:
>> On 10/14/2011 09:39 AM, Feng Wei wrote:
>>>
>>> 2011/10/14 David Henningsson<david.henningsson at canonical.com>:
>>>>
>>>> On 10/14/2011 04:47 AM, Feng Wei wrote:
>>>>>
>>>>> Hi Liam, Mark, Colin, and all,
>>>>>    I study the codes in pulseaudio and alsa ucm patch recently, and
>>>>> create a page of my study result. I appreciate your feedback. The page
>>>>> is at
>>>>>
>>>>> https://wiki.linaro.org/WorkingGroups/Middleware/Multimedia/Specs/1111/AudioIntegration/UCMPulseAudio/Analyzation.
>>>>>    Also if needed, I'm glad to contribute to the integration of alsa
>>>>> ucm in pulseaudio.
>>>>>    Thank you.
>>>>
>>>> Oh, nice diagrams :-) Some of them might be useful additions to the
>>>> PulseAudio wiki.
>>>
>>> Thanks :-)
>>>>
>>>> I think the modelling of UCM concepts onto PulseAudio concepts is an
>>>> important discussion. In PulseAudio, profiles are mainly connected to
>>>> device
>>>> strings, how to open the devices, channels supported, whereas ports are
>>>> just
>>>> alsa mixer kcontrol changes. UCM verbs, as I understand it, contain both.
>>>
>>> My understanding is profile:port and verb:device/modifier are both
>>> hierarchical. e.g. we have an alsa device string hw:0,0, and some
>>> mixer controls for route speaker or headset. In pa profile, we
>>> describe a profile output:analog-stereo with two ports, one for
>>> speaker, and the other for  headset. In ucm, we define verb "hifi" and
>>> two excluded devices speaker and headset, both of the devices have
>>> PlaybackPCM hw:0,0. And we can also define two modifiers to switch
>>> between speaker and headset. So we can create profile by verb and
>>> create profile input/output mappings by devices(merge the same hw
>>> device) and create ports by modifier. I'm not sure if it break the
>>> original ucm concepts, but I think it can work.
>>
>> There is also the "Use Case" concept in UCM, Is there always exactly one
>> verb for every use case? If not, one might wonder if "Use Case" or "Verb" is
>> what should correspond to the "Profile" concept.
> verb is equal to use case. "use case" is a concept and verb is in the
> source code.

Ok.

>> Card, Sink/Source, Profile and Port are the core concepts in PulseAudio. I
>> think UCM should use alsa-sink, alsa-card and alsa-source, but the rest of
>> the stuff: pa_alsa_profile_*, pa_alsa_path_*, pa_alsa_mapping - in short,
>> everything in alsa-mixer.h, I don't think the UCM implementation should
>> touch them. They are too tightly coupled with the existing ideas of how to
>> map ALSA kcontrols to Profiles and Ports, something that UCM does in its own
>> way. So in my opinion, you should forget about mappings - it's Profile and
>> Port (and Sink/Source) we need to match against.
> Actually we must map the concepts because ucm is designed for abstract
> the complicated kcontrol. In my mind, if we use ucm in pa, the
> original profile configuration files and mixer configuration files
> will be replaced by ucm configuration files.

I beg to differ: In UCM, PulseAudio is not modifying the mixer controls 
directly, it's just doing calls to alsa ucm library to enable and 
disable stuff verbs/devices/etc. That's why we should not map against 
existing routines that are mainly for modifying mixer controls.

Removing the original profile configuration files might be possible in 
an embedded scenario, but for all hundreds of different 
snd-hda-intel/AC'97/etc configurations out there, writing UCM 
configurations to fit all of them is just not scalable. (If so, one 
would have to write an auto-UCM tool that autogenerates UCM profiles 
based on present hardware.)

-- 
David Henningsson, Canonical Ltd.
http://launchpad.net/~diwic