Proposal: new audio framework

[Tetsuya Isaki <isaki%pastel-flower.jp@localhost>]

Hi all,

I'd like to propose a new audio framework (which I call AUDIO2).

 http://www.netbsd.org/~isaki/audio2-20190401.diff.gz

Audio driver since 8.0 has in-kernel mixing feature and it's really
exciting.  But also has so many problems.
 * unstable including locking issues.
 * bad playback quality and high load (especially on slow machines).
 * high latency.
 * does not support drivers with uncommon characteristics.
   For example, vs(4) hardware frequency is 15625Hz but audio.c can
   not attach such devices (as it is).
 * interface was silently changed so several hardware drivers have
   no longer worked.
 * There is a lot of unmaintained(no longer used) code.

So I've reimplemented whole audio framework to fix them.  It is mostly
worked fine for me.
 * stable.
 * good playback quality and lightweight even on 68030.
   The average of system load ("sy" column by vmstat) on playing single
   1ch/8000Hz mulaw on x68k (68030/30MHz/12MB real machine) is:
   about 50% on -current,
   about 10% on AUDIO2.
   (FYI, it's about 4% on NetBSD7.)
 * better latency.
   current latency is normally about 3*50=150msec in default,
   AUDIO2  latency is normally about 2*40=80msec  in default.
 * smaller textsize (and probably memory usage).
   For example, amiga/GENERIC kernel has three old-style audio drivers and
   AUDIO2 modifies two of these already.  At this moment it reduces kernel
   size about 35KB.  In the end we will be able to reduce it more.
 * well support for non-PCM hardware.
 * well consideration about half duplex hardware.
 * provide many tests.
 * introduce sysctl hw.wsbellN.mute to be able to mute individually.

AUDIO2 requires explicit few interface changes, so all hardware drivers
must be catched up.  Current status is:
 * works: arcofi(4), auich(4), bba(4), eap(4), hdafg(4), uaudio(4),
          vs(4), vsaudio(4)
 * compiled but not tested: audioamd(4), aucc(4), melody(4), repulse(4)
 * works but more works are required: sb(4), pad(4), spkr_audio
Other drivers not listed here are not supported yet.

There is one thing I'm worried about.  AUDIO2 requires more strict
blocksize and buffersize for hardware drivers.  It will be a hard
work if there are any hardware that does not satisfy the requirements.
# Although I believe there are no such hardware...

Some of TODOs:
 * remove all ifdef AUDIO2.
   It was needed to confirm non-AUDIO2 kernel build.
 * support all hardware drivers. (need your help!)
 * support NetBSD8-like multiuser mode?
 * mmap is not well tested.
 * translate or cleanup Japanese comments which is left in source code.
 * convert my local tests (which is not included in the patch) into ATF.

Any comments?
---
Tetsuya Isaki <isaki%pastel-flower.jp@localhost / isaki%NetBSD.org@localhost>