[alsa-devel] right way to enumerate pcm devices

[Takashi Iwai]

On Wed, 13 Feb 2019 15:13:28 +0100,
sylvain.bertrand at gmail.com wrote:
> 
> On Wed, Feb 13, 2019 at 07:25:13AM +0100, Takashi Iwai wrote:
> > It's only the matter of alsa-lib card config.  Just due to heuristic
> > reason, the secondary device is assigned as iec958 as default.  There
> > are explicit whitelist setup in alsa-lib/src/conf/cards/USB-Audio.conf
> > for the card that behave differently.  You'd need to adjust
> > accordingly.
> 
> Tell me if I did understand you right:
> 
> I cannot trust the hint system to select proper pcm devices for, let's say the
> mic of my USB cam.

It can be seen rather as a bug in alsa-lib card config.  The card
config should be fixed to match with this badly behaving device.

> I would have to ignore "mostly" the configuration system (the major exception
> would be the default pcm device) and build myself the pcm devices from the info
> I can get from the hardware device (hardware mixing, input and/or output,
> number of channels/etc).

Or report the bug to get it fixed.

> I would have to cherry pick configuration defined pcm devices for specific
> modes, like surroundX, only if the "basic user" explicitely requests such modes.

... if you want to fix it by yourself, right.

> The advanced user should override the default pcm device if he/she wants to
> do/fix tricky sound thingies.

The advanced user should report the bug report, not ignore and work
around it, too :)


Takashi

> 
> ----
> 
> To summarize:
> 	- show always the pcm default
> 	- build custom pcm devices based on hardware info, and show them
> 	- for "special" modes, likes surroundX, show the related configuration
> 	  defined pcm devices only if the "basic" user want to fool around with
> 	  them.
> 
> -- 
> Sylvain
>