Re: About ALSA dummy module: support customized mixer volume leveling

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On Thu, Sep 8, 2022 at 4:16 PM Takashi Iwai <tiwai@xxxxxxx> wrote:
>
> On Thu, 08 Sep 2022 07:26:02 +0200,
> YJ Lee wrote:
> >
> > Hello Takashi (and the alsa community),
> >
> > This is YJ Lee from chromium.org.
> >
> > I'm thinking about extending the ALSA dummy module to support
> > customized volume leveling. It will be very useful to test devices
> > with different volume granularity. Currently this module is using
> > hard-coded mixer volume leveling, from min=-50 to max=100.
> >
> > See L716: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git/tree/sound/drivers/dummy.c?h=queue/5.19#n716
> >
> > My plan (A) is to expose 2 more additional module parameters and
> > replace a few occurrences, from L742-750.
> >
> > Another plan (B) is to leverage the current existing module
> > parameter:model, and make the dummy-module to be able to accept models
> > with customized volume leveling. New dummy models can be provided as
> > configuration files, and be used in the same way as how currently
> > existing dummy models (L146-213) are used. However, it's a bit
> > over-engineering from the original purpose.
> >
> > What do you think about these plans? Any insight you (and the alsa
> > community) can provide will be greatly appreciated.
>
> Only for volume min/max, module options may be an easier way, IMO.
>
> OTOH, if we want to adjust more stuff, another possibility is to
> extend the proc file.  It currently supports the dynamic changes of
> PCM parameters, but we can extend it or add a new proc file for
> adjusting other stuff, too.  So the question is what else we want to
> allow changing.
>
>
> thanks,
>
> Takashi

Hi Takashi,

Thanks for your quick reply! I can't express my gratitude enough. Will
stick with plan (A).

Additionally, I'll take some time to read it and learn how to use the
proc file. Compared with snd-dummy, I've plugged in a physical USB
headset and saw some read-only files (usb*) under /proc/asound/cardX.
By extending the proc file, are you suggesting we can change those
into writable so ALSA will understand and make corresponding changes,
(e.g. 'change' the dummy card into a USB sound card)? Can you tell me
more about how to extend or add a new proc file (as a separate topic)?

Again, greatly appreciated.

Best,
YJ



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