About ALSA dummy module: support customized mixer volume leveling

[YJ Lee]

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.

Best,
YJ