[pulseaudio-discuss] Configuration system proposal (was: Toggling hardware volume for a card or port in pavucontrol)

[Arun Raghavan]

Hi folks,
Tanu already brought this up, posting some context:

On Fri, 2016-01-15 at 19:52 +0200, Tanu Kaskinen wrote:
> On Wed, 2016-01-13 at 16:19 +0200, Tanu Kaskinen wrote:
> > Hi,
> > 
> > Related to previous discussions[1][2][3] about dealing with volume
> > on
> > certain type of usb sound cards, I'd like to make it possible to
> > enable
> > and disable hardware volume for individual cards and/or ports in
> > pavucontrol.
> > 
> > Here's the specific use case: the Terratec Aureon Dual USB sound
> > card
> > has a single output jack that can used in both analog and digital
> > modes
> > (there are other similar usb sound cards too). PulseAudio has no
> > way to
> > know which mode is in use. Hardware volume works only in the analog
> > mode. Currently that means that PulseAudio's volume control has no
> > effect in the digital mode, because PulseAudio controls a mixer
> > element
> > that doesn't do anything.
> > 
> > I want to disable hardware volume for that card by default, because
> > that's the only safe default. That reduces the audio quality a bit,
> > however, so it would be good to allow concerned users to enable
> > hardware volume for the card without too much hassle.
> > 
> > I'd like some feedback to guide the design:
> > 
> > 0) Is this feature worth the maintenance burden the new code
> > causes, or
> > should I just forget about this? (My answer: it's worth doing.)
> > 
> > 1) Should the client API be specific to alsa, or should it be added
> > to
> > the core interface? A third option exists too: don't make it
> > specific
> > to alsa, but implement the client API in a module with a protocol
> > extension, and hook to the new module from alsa code. (My answer:
> > core.)
> 
> Arun commented in IRC that another alternative would be to use the
> "configuration system"[1] that Arun would like to implement. Although
> I
> had some reservations at first, I now think that the proposed
> configuration system fits this use case well, so I have nothing
> against
> doing the hardware volume toggle implementation that way. The recent
> discussion about the configuration system has been only between Arun
> and me in IRC, however, so it may be that others disagree about the
> desirability of the new system. Feedback about that, too, would be
> very
> welcome.
> 
> [1] https://wiki.freedesktop.org/www/Software/PulseAudio/Documentation/Developer/ConfigurationSystem/

Comments would indeed be welcome, and I'm happy to expand on any of the
bits that aren't clear as well.

I'm not sure exactly when I'll be able to get to this, but having the
basic ideas hammered out should make it easier to get started whenever
time allows (or for anyone else to jump in as well).

Cheers,
Arun