Merge isaki-audio2 branch, the overhaul of audio subsystem.
- Interrupt-oriented system rather than thread-oriented.
- Improve stability, quality and performance.
- Split playback and record cleanly. Improve halfduplex support.
- Many bugs are fixed including deadlocks, resource leaks, abuses, etc.
- Simplify audio filter mechanism. The encoding/channels/frequency
conversions are completely handled in the upper layer. So the hard-
ware driver only converts its hardware encoding (if necessary).
- audio_hw_if changes:
- Obsoletes query_encoding and add query_format instead.
- Obsoletes set_params and add set_format instead.
- Remove drain, setfd, mappage.
- The call sequences are changed.
- ioctl AUDIO_GETFD/SETFD, AUDIO_GETCHAN/SETCHAN are obsoleted.
- ioctl AUDIO_{QUERY,GET,SET}FORMAT are introduced.
- cleanup config attributes: au*conv and mulaw.
- All hardware drivers should follow it (I've done as much as possible).

Some file paths are changed:
- dev/audio.c -> dev/audio/audio.c (rewritten)
- dev/audiovar.h -> dev/audio/audiovar.h
- dev/audio_dai.h -> dev/audio/audio_dai.h
- dev/audio_if.h -> dev/audio/audio_if.h
- dev/audiobell.c -> dev/audio/audiobell.c
- dev/audiobellvar.h -> dev/audio/audiobellvar.h
- dev/mulaw.[ch] -> dev/audio/mulaw.[ch] + dev/audio/alaw.c

branches: 1.5.20; 1.5.24;
Add common audio converters for software volume control. Only supports
slinear16_le and slinear16_be for now.

Convert pad(4) to use the new converters.

branches: 1.4.22; 1.4.38;
PR# kern/39899: audio attach with pad(4) segfaults

Make sure pad pulls in auconv mulaw support.

branches: 1.3.6; 1.3.14;
use new "defpseudodev" where appropriate, and remove dummy interface
attribute definitions which were only to trick config(8)

branches: 1.2.2; 1.2.4; 1.2.6; 1.2.8; 1.2.18; 1.2.24; 1.2.26; 1.2.28; 1.2.30; 1.2.32;
Implement volume controls for pseudo audio device.

Add pseudo audio device driver. With this pseudo-device, audio played back
via the standard audio interfaces is redirected back to userland as raw
PCM data on /dev/padN.

One example usage is to stream audio to an AirTunes compatible device using
rtunes (http://www.nazgul.ch/dev_rtunes.html), ie:

$ rtunes - < /dev/pad0
$ mpg123 -a /dev/sound1 blah.mp3

Another option is to capture audio output from eg. Real Player, by simply
instructing Real Player to output to /dev/sound1, and running:

$ cat /dev/pad0 > blah.pcm

Allow "attach" directives to have interface attributes, rather than
restricting them to plain attributes only.

Consider the case of a USB controller for which there is a generic
driver with multiple front-end bus attachments. Normally, a USB
controller driver carries the interface attribute necessary to attach
a USB root hub / bus instance. But, on some systems, a platform-specific
attachment may have other nodes in the device tree that are needed to
enable or configure the USB controller, that appear in the device tree
as children of the USB controller. These devices may need to attach
using a different interface attribute, unrelated to USB functionality.

Prior to this change, it would have been necessary to put the platform-
specific interface attribute onto the generic driver. But that comes
with side-effects on other platforms where that driver might be used.

In an ideal scenario, an attachment with special requirements should be
able to carry attachment-specific interface attributes to handle those
requirements, and this change enables that. When searching for prospective
parents, the autoconfiguration machinery first consults the cfdriver for
interface attributes, as before, and checks potential cfattach instances
if a cfdriver match isn't found.

A separate list of attachment-specific interface attributes is maintained
by the autoconfiguration machinery in the kernel. They are not hung off
of the cfattach directly, as they are with cfdriver instances, because
config(1) does not control the cfattach; individual driver front-ends do.
By arranging it this way, there is minimal impact to non-generated code.

This changes the "cfattachinit" structure, and thus changes the ABI for
kernel modules.

Bienvenidos a NetBSD 11.99.5!

Revert to previous.

This change broke the intention of recent changes to pad(4).

The solution to address PR/57436 must be done in bta2dpd(8).

Fix previous.

The previous commit was misleading due to the flag names used.

The rationale for this change is that it is ok to return EAGAIN on first
read as playback has not started. Then it shoud wait on every subsequent read.

This is what makes the high precsision throttling of pad(4), for which these
degree of fine-grained sleeps are not possible in userland. This is a
requirement of users of pad(4) such as bta2dpd(8).

Fix logic for timing.

Addresses PR/57436.

XXX pullup-10.

Don't overflow when scaling 32bit samples.

No longer use AUDIO_INTERNAL_BITS but rely on passed audio format.

Write slinear_le 16bit samples, independent from platform and
AUDIO_INTERNAL_BITS.

Pace I/O timing to match the audio interface.
Enable interrupts while copying buffers.

branches: 1.78.4;
For device modules that provide both auto-config and /dev/xxx
interfaces, make sure that initialization and destruction
follow the proper sequence. This is triggered by the recent
changes to the devsw stuff; per riastradh@ the required call
sequence is:

devsw_attach()
config_init_component() or config_cf*_attach()
...
config_fini_component() or config_cf*_detach()
devsw_detach()

While here, add a few missing calls to some of the detach
routines.

Testing of these changes has been limited to:
1. compile without build break
2. no related test failures from atf
3. modload/modunload work as well as
before.

No functional device testing done, since I don't have any
of these devices. Let me know of any damage I might cause
here!

XXX Some of the modules affected by this commit are already
XXX broken; see kern/56772. This commit does not break
any additional modules (as far as I know).

driver(9): devsw_detach never fails. Make it return void.

Prune a whole lotta dead branches as a result of this. (Some logic
calling this is also wrong for other reasons; devsw_detach is final
-- you should never have any reason to decide to roll it back. To be
cleaned up in subsequent commits...)

XXX kernel ABI change to devsw_detach signature requires bump

pad(4): Do harmless, not harmful, integer truncation.

Reported-by: syzbot+917ff3551897f1a99cf6@syzkaller.appspotmail.com

pad(4): Explain what's wrong with using device pointers like this.

...and why the kernel lock is not enough.

pad(4): Omit unused sc_blksize.

pad(4): Refactor for clarity, and fix locking bugs.

- Don't touch sc_buflen outside sc_intr_lock.

- Omit needless broadcast in pad_halt_output -- nothing wakes on the
new condition (sc_buflen == 0), so this can't make a difference
except possibly in buggy code.

- Sprinkle KASSERTs.

pad(4): Destroy the callout when done.

Should not be possible for it to be pending or firing at this point,
because we have detached the audio(4) child and so it should have
halted output.

pad(4): Make this exclusively a cloning device.

padN numbering never corresponded with audioM numbering except by
accident, so the non-cloning device never worked reliably for
scripting. This simplifies the logic substantially.

While here, fix drvctl detach race.

pad(4): Sort includes. Add missing includes to padvar.h.

pad(4): Fix some locking.

- No need for sc_cond_lock.
- Issue cv_broadcast under the correct lock.
- Use callout_halt, not haphazard callout_stop.
- IPL_SOFTCLOCK for a mutex taken from a callout.

pad(4): Some incomplete tidying.

- Put pseudo-device softc setup/teardown back in pad_attach/detach,
not in the cdev/fops operations which are about file descriptors.
- Remove unnecessary sc_dying flag.
- Omit needless config_deactivate(sc->sc_audiodev); the only effect
of this is already done by config_detach anyway, which is done in
the same context.
- Issue config_detach_children and free softc stuff in the right
order.
- Omit needless `if (sc == NULL) return ENXIO'.

Survives eight parallel t_mixerctl tests many times over on an
8-thread/4-core machine.

XXX TODO:
- Remove padconfig; it is not appropriate to hold a mutex over
sleeping allocation or autoconf config_attach operations. This
should be done another way.
- Fix agreement of sc_condvar with locks: is it sc_cond_lock or
sc_intr_lock? Can't be both; unclear why both exist.
- Determine whether both cdev and fops are really needed -- it is
confusing to have two types of paths into all this logic, and it
seems to me only one of them should be necessary.

pad(4): Take kernel lock around autoconf stuff.

This is not really enough -- the padconfig locking logic violates
rules about sleeping while holding locks, might be deadlocky, and may
also be racy. But, it'll serve to make progress.

pad(4): run the callout if the buffer is saturated instead of returning

reverts to the same behavior as in -8 and -9. prevents immediate failures
and device timeouts if there's a slight delay in the buffer being
consumed.

this is reproducible with the example in the man page that uses
ffmpeg to record the output of audioplay:

$ ffmpeg -f s16le -ar 44100 -ac 2 -i /dev/pad0 output.wav
$ audioplay -d /dev/audio1 input.wav

if output.wav already exists, ffmpeg will prompt for confirmation
to overwrite as soon as audioplay starts, causing a noticable delay,
followed by a write failure that causes audioplay to immediately
exit.

branches: 1.65.10;
Make start_input/halt_input optional if the driver has no recording,
make start_output/halt_output optional if the driver has no playback.
And remove such never called functions.

Make calling get_props() lockless.
get_props() of all MD drivers now can be called without sc_lock.

branches: 1.63.4;
Fix return value. fo_poll expects revents, not errno.

Style fixes. No functional changes intended.
- Rename some functions for consistency.
- Rearrange some functions for readability.
- Unify to struct pad_softc.

Don't call next callout when an error occurs in start_output.

pad(4)'s output format is LE even on big endian arch.

Merge isaki-audio2 branch, the overhaul of audio subsystem.
- Interrupt-oriented system rather than thread-oriented.
- Improve stability, quality and performance.
- Split playback and record cleanly. Improve halfduplex support.
- Many bugs are fixed including deadlocks, resource leaks, abuses, etc.
- Simplify audio filter mechanism. The encoding/channels/frequency
conversions are completely handled in the upper layer. So the hard-
ware driver only converts its hardware encoding (if necessary).
- audio_hw_if changes:
- Obsoletes query_encoding and add query_format instead.
- Obsoletes set_params and add set_format instead.
- Remove drain, setfd, mappage.
- The call sequences are changed.
- ioctl AUDIO_GETFD/SETFD, AUDIO_GETCHAN/SETCHAN are obsoleted.
- ioctl AUDIO_{QUERY,GET,SET}FORMAT are introduced.
- cleanup config attributes: au*conv and mulaw.
- All hardware drivers should follow it (I've done as much as possible).

Some file paths are changed:
- dev/audio.c -> dev/audio/audio.c (rewritten)
- dev/audiovar.h -> dev/audio/audiovar.h
- dev/audio_dai.h -> dev/audio/audio_dai.h
- dev/audio_if.h -> dev/audio/audio_if.h
- dev/audiobell.c -> dev/audio/audiobell.c
- dev/audiobellvar.h -> dev/audio/audiobellvar.h
- dev/mulaw.[ch] -> dev/audio/mulaw.[ch] + dev/audio/alaw.c

branches: 1.58.2;
pad(4) mixer has only 1 channel, so return EINVAL in the case other than 1.

This fixes the following strange output of mixerctl(1):

outputs.master=255,0
inputs.dac=255,0

Revert to rev.1.53.
I accidentally committed the netbsd-8 branch file in rev.1.54.

Since we need an int paramater, and uio_resid is size_t cast it to int
to avoid warnings from the ever friendly compiler... (check that size if
in range was already made).

Open code min() so we don't need to find its prototype ...

pad(4) mixer has only 1 channel, so return EINVAL in the case other than 1.

This fixes the following strange output of mixerctl(1):

outputs.master=255,0
inputs.dac=255,0

Rename min/max -> uimin/uimax for better honesty.

These functions are defined on unsigned int. The generic name
min/max should not silently truncate to 32 bits on 64-bit systems.
This is purely a name change -- no functional change intended.

HOWEVER! Some subsystems have

#define min(a, b) ((a) < (b) ? (a) : (b))
#define max(a, b) ((a) > (b) ? (a) : (b))

even though our standard name for that is MIN/MAX. Although these
may invite multiple evaluation bugs, these do _not_ cause integer
truncation.

To avoid `fixing' these cases, I first changed the name in libkern,
and then compile-tested every file where min/max occurred in order to
confirm that it failed -- and thus confirm that nothing shadowed
min/max -- before changing it.

I have left a handful of bootloaders that are too annoying to
compile-test, and some dead code:

cobalt ews4800mips hp300 hppa ia64 luna68k vax
acorn32/if_ie.c (not included in any kernels)
macppc/if_gm.c (superseded by gem(4))

It should be easy to fix the fallout once identified -- this way of
doing things fails safe, and the goal here, after all, is to _avoid_
silent integer truncations, not introduce them.

Maybe one day we can reintroduce min/max as type-generic things that
never silently truncate. But we should avoid doing that for a while,
so that existing code has a chance to be detected by the compiler for
conversion to uimin/uimax without changing the semantics until we can
properly audit it all. (Who knows, maybe in some cases integer
truncation is actually intended!)

branches: 1.52.2; 1.52.4;
Fix typo in previous. mea culpa, mea culpa, mea maxima culpa

Unitialized variable - CID/1428657

Fix pad on systems with many cores/cpus:

* Introduce a lock to serialize attach/detach of pad devices.
* Forcefully detach children of pad on close.
* Be more carefull in pad_open with regards to config_detach only
if new instances of the pad device are created and fail to open.

Addresses PR kern/52889.

These changes were developed with and tested by pgoyette@.

If config_fini_component() fails (due to device driver busy), don't
discard its error value when re-attaching the devsw. If the devsw
is successfully re-attached and we return success, the module will
get detached anyway. And, since the device is actually busy, we'll
eventually panic.

Thanks to nat@ for providing the reproduction instructions.

XXX A driver-busy condition will currently still trigger the error
XXX message from config_fini_component()
XXX configure: attachment `pad' of `pad' driver fini failed: 16
XXX This will be addresses separately by having pad maintain its own
XXX ref-count and not relying on config_fini_component() to detect
XXX the busy state.

Use config(1) and IOCONF= to generate most of the auto-config data
structures. (Note that bin/52823 documents the reasons for still
requiring hand-crafted cfattach structures.)

Remove the correct extra #endif

:)

remove extra #endif left in previous commit.

Replace manipulation of individual config structures with calls to
config_{init,fini}_component()

Rework so that module infrastructure is provided even when the module
is built-in to the kernel.

XXX pullup-8?

add fo_name so we can identify the fileops in a simple way.

The pad module will now compile with WARNS=5.

If a particular pad device is opened, ie pad1 then configure and use pad1
if it is not already configured.

This improves scriptability as you will know the particular pad(4) device
you have opened.

pad(4) devices still have a cloning interface if pad device (minor
number 254) is opened it will attach the next free device. This action
can be repeated.

XXX update MAKEDEV scripts to make /dev/pad the cloning device.

Ok christos@.

Return early from read if kpause is interrupted by a signal.

Pad is now clones its device, attaching upon open and detaching upon close.
This means that only one pad device is required in /dev.

The code contains a compile time limit of 128 units.

Ok christos@.

sc_audiodev should be defined as a device_t as this is what audio_attach_mi
returns.

Use defines to specify pad audio format. NFCI.

Ok christos@.

Style change.

Simplification of rate limiter. It now works uni/multiprocessor.

sc_bytes_count needs to be set in pad_audio_open not pad_open.

Express BYTESTOSLEEP as an 64 bit integer.
Use BYTESTOSLEEP in expresson of BYTES_PER_SEC.

branches: 1.32.2;
Add infrastructure for modularization of audio, midi, and sequencer

remove checks for failure after memory allocation calls that cannot fail:

kmem_alloc() with KM_SLEEP
kmem_zalloc() with KM_SLEEP
percpu_alloc()
pserialize_create()
psref_class_create()

all of these paths include an assertion that the allocation has not failed,
so callers should not assert that again.

Add missing sc_bytes_count.

Rework of previous.
Math for BYTESTOSLEEP and TIMENEXTREAD is now correct.

branches: 1.28.4;
Update pad due to changes in audio. sc_bytes_count and BYTESTOSLEEP are
no longer required.

Don't hold the thread_lock between successive calls to sc_intr as it
breaks mixing.

This will help passing the atf test. Changes to audio.c to ensue this
will be in a followup commit.

branches: 1.26.2;
pad(4) must be open before corresponding audio device is opened.

OK christos@

branches: 1.25.2;
KNF. Remove extra spaces. No functional change.

Allow reads from pad(4) less or greater than PAD_BLKSIZE.

Ensure that audio data is ready before reading.
Addresses PR 39204.

OK jmcneil@.

Wrap up calls to sc_intr in kpreempt[en/dis]able.

This commit was approved by christos@

branches: 1.22.2;
Add common audio converters for software volume control. Only supports
slinear16_le and slinear16_be for now.

Convert pad(4) to use the new converters.

branches: 1.21.2;
Add d_discard to all struct cdevsw instances I could find.

All have been set to "nodiscard"; some should get a real implementation.

branches: 1.20.2;
sprinke __diagused

branches: 1.19.8; 1.19.12;
get rid of a variable which is no longer used after the demise of splaudio

splaudio is no more

Merge jmcneill-audiomp3 branch, which is derived from ad-audiomp2. From
the original ad-audiomp branch notes:

Add MP locking to the audio drivers.

Making the audio drivers MP safe is necessary before efforts
can be made to make the VM system MP safe.

The are two locks per device instance, an ISR lock and
a character device lock. The ISR lock replaces calls to
splaudio()/splx(), and will be held across calls to device
methods which were called at splaudio() before (e.g.
trigger_output). The character device lock is held across
calls to nearly all of the methods, excluding some only
used for initialization, e.g. get_locks.

Welcome to 5.99.57.

branches: 1.16.8; 1.16.10;
- return EIO if audio data is received and /dev/pad isn't open
- give a better description for AUDIO_GETDEV

Don't print spammy message if read is interrupted (ctrl-c)
while waiting for data.

fix field initializers

Add support to be built as a kernel module.

branches: 1.12.2; 1.12.4;
If the device does not exist, return ENXIO, as is customary, instead of
ENODEV. Ok jmcneill@.

'boot -z' bogons

branches: 1.10.2; 1.10.4; 1.10.6; 1.10.8;
fix device is not split warning

remove a KASSERT which is wrong since audio(4)'s device/softc were split

branches: 1.8.4;
Replace homegrown pad_find_softc() with device_lookup_private().

Use 2-clause license.

branches: 1.6.2; 1.6.4; 1.6.6;
Split device_t and softc for audio(4), and other related cosmetic changes.

Add methods to detach self and children.

branches: 1.4.6; 1.4.8; 1.4.12;
Merge jmcneill-pm branch.

branches: 1.3.2;
Match the docs: MUTEX_DRIVER/SPIN are now only for porting code written
for Solaris.

branches: 1.2.2; 1.2.4; 1.2.6; 1.2.8; 1.2.10;
Implement volume controls for pseudo audio device.

Add pseudo audio device driver. With this pseudo-device, audio played back
via the standard audio interfaces is redirected back to userland as raw
PCM data on /dev/padN.

One example usage is to stream audio to an AirTunes compatible device using
rtunes (http://www.nazgul.ch/dev_rtunes.html), ie:

$ rtunes - < /dev/pad0
$ mpg123 -a /dev/sound1 blah.mp3

Another option is to capture audio output from eg. Real Player, by simply
instructing Real Player to output to /dev/sound1, and running:

$ cat /dev/pad0 > blah.pcm

Pace I/O timing to match the audio interface.
Enable interrupts while copying buffers.

branches: 1.16.10;
pad(4): Omit unused sc_blksize.

pad(4): Sort includes. Add missing includes to padvar.h.

pad(4): Fix some locking.

- No need for sc_cond_lock.
- Issue cv_broadcast under the correct lock.
- Use callout_halt, not haphazard callout_stop.
- IPL_SOFTCLOCK for a mutex taken from a callout.

branches: 1.13.14;
Style fixes. No functional changes intended.
- Rename some functions for consistency.
- Rearrange some functions for readability.
- Unify to struct pad_softc.

Merge isaki-audio2 branch, the overhaul of audio subsystem.
- Interrupt-oriented system rather than thread-oriented.
- Improve stability, quality and performance.
- Split playback and record cleanly. Improve halfduplex support.
- Many bugs are fixed including deadlocks, resource leaks, abuses, etc.
- Simplify audio filter mechanism. The encoding/channels/frequency
conversions are completely handled in the upper layer. So the hard-
ware driver only converts its hardware encoding (if necessary).
- audio_hw_if changes:
- Obsoletes query_encoding and add query_format instead.
- Obsoletes set_params and add set_format instead.
- Remove drain, setfd, mappage.
- The call sequences are changed.
- ioctl AUDIO_GETFD/SETFD, AUDIO_GETCHAN/SETCHAN are obsoleted.
- ioctl AUDIO_{QUERY,GET,SET}FORMAT are introduced.
- cleanup config attributes: au*conv and mulaw.
- All hardware drivers should follow it (I've done as much as possible).

Some file paths are changed:
- dev/audio.c -> dev/audio/audio.c (rewritten)
- dev/audiovar.h -> dev/audio/audiovar.h
- dev/audio_dai.h -> dev/audio/audio_dai.h
- dev/audio_if.h -> dev/audio/audio_if.h
- dev/audiobell.c -> dev/audio/audiobell.c
- dev/audiobellvar.h -> dev/audio/audiobellvar.h
- dev/mulaw.[ch] -> dev/audio/mulaw.[ch] + dev/audio/alaw.c

branches: 1.11.6; 1.11.10;
Pad is now clones its device, attaching upon open and detaching upon close.
This means that only one pad device is required in /dev.

The code contains a compile time limit of 128 units.

Ok christos@.

sc_audiodev should be defined as a device_t as this is what audio_attach_mi
returns.

pad blocksize 1024 -> 8192. Helps when sleeping in rate limiter.

branches: 1.8.2;
Rework of previous.
Math for BYTESTOSLEEP and TIMENEXTREAD is now correct.

Update pad due to changes in audio. sc_bytes_count and BYTESTOSLEEP are
no longer required.

branches: 1.6.2; 1.6.4;
Allow reads from pad(4) less or greater than PAD_BLKSIZE.

Ensure that audio data is ready before reading.
Addresses PR 39204.

OK jmcneil@.

branches: 1.5.2;
Add common audio converters for software volume control. Only supports
slinear16_le and slinear16_be for now.

Convert pad(4) to use the new converters.

branches: 1.4.8; 1.4.24;
Merge jmcneill-audiomp3 branch, which is derived from ad-audiomp2. From
the original ad-audiomp branch notes:

Add MP locking to the audio drivers.

Making the audio drivers MP safe is necessary before efforts
can be made to make the VM system MP safe.

The are two locks per device instance, an ISR lock and
a character device lock. The ISR lock replaces calls to
splaudio()/splx(), and will be held across calls to device
methods which were called at splaudio() before (e.g.
trigger_output). The character device lock is held across
calls to nearly all of the methods, excluding some only
used for initialization, e.g. get_locks.

Welcome to 5.99.57.

branches: 1.3.6; 1.3.28; 1.3.30;
fix device is not split warning

branches: 1.2.4;
Use 2-clause license.

branches: 1.1.2; 1.1.4; 1.1.6; 1.1.8; 1.1.18; 1.1.24; 1.1.26; 1.1.28; 1.1.30;
Implement volume controls for pseudo audio device.

Add common audio converters for software volume control. Only supports
slinear16_le and slinear16_be for now.

Convert pad(4) to use the new converters.

branches: 1.6.8; 1.6.24;
Merge jmcneill-audiomp3 branch, which is derived from ad-audiomp2. From
the original ad-audiomp branch notes:

Add MP locking to the audio drivers.

Making the audio drivers MP safe is necessary before efforts
can be made to make the VM system MP safe.

The are two locks per device instance, an ISR lock and
a character device lock. The ISR lock replaces calls to
splaudio()/splx(), and will be held across calls to device
methods which were called at splaudio() before (e.g.
trigger_output). The character device lock is held across
calls to nearly all of the methods, excluding some only
used for initialization, e.g. get_locks.

Welcome to 5.99.57.

branches: 1.5.4; 1.5.6;
Use le16enc()/be16enc() to encode LE/BE values back into the audio stream.
This fixes the tests/dev/audio test on my macppc box.

While I'm here, use le16dec()/be16dec() directly instead of rewriting them.

branches: 1.4.4; 1.4.6; 1.4.8;
Catch up to audio(4) device_t/softc split.

branches: 1.3.8; 1.3.10; 1.3.14; 1.3.16;
mutex.h is implied by condvar.h
param.h is required for xen

Use 2-clause license.

branches: 1.1.2; 1.1.4; 1.1.6; 1.1.8; 1.1.18; 1.1.24; 1.1.26; 1.1.28; 1.1.30;
Implement volume controls for pseudo audio device.

Add common audio converters for software volume control. Only supports
slinear16_le and slinear16_be for now.

Convert pad(4) to use the new converters.

branches: 1.3.8; 1.3.24;
Merge jmcneill-audiomp3 branch, which is derived from ad-audiomp2. From
the original ad-audiomp branch notes:

Add MP locking to the audio drivers.

Making the audio drivers MP safe is necessary before efforts
can be made to make the VM system MP safe.

The are two locks per device instance, an ISR lock and
a character device lock. The ISR lock replaces calls to
splaudio()/splx(), and will be held across calls to device
methods which were called at splaudio() before (e.g.
trigger_output). The character device lock is held across
calls to nearly all of the methods, excluding some only
used for initialization, e.g. get_locks.

Welcome to 5.99.57.

branches: 1.2.10; 1.2.32; 1.2.34;
Use 2-clause license.

branches: 1.1.2; 1.1.4; 1.1.6; 1.1.8; 1.1.18; 1.1.24; 1.1.26; 1.1.28; 1.1.30;
Implement volume controls for pseudo audio device.