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.
* Use the trigger interface.
* Permit different encodings for record and playback.
* Set AUDIO_PROP_INDEPENDENT.
* Fix the mmap(2) hole again.
* Use 16-bit mode for a-law and u-law playback.
