sound: Update COPYRIGHT notices

Only to files I've currently made significant contributions to.

Sponsored by: The FreeBSD Foundation
MFC after: 1 week

snd_dummy: Fix callout(9) races

Use callout_init_mtx(9) to associate the callback with the driver's
lock. Also make sure the callout is stopped properly during detach.

While here, introduce a dummy

snd_dummy: Fix callout(9) races

Use callout_init_mtx(9) to associate the callback with the driver's
lock. Also make sure the callout is stopped properly during detach.

While here, introduce a dummy_active() function to know when it's
appropriate to stop or not reschedule the callout.

Sponsored by: The FreeBSD Foundation
MFC after: 2 days
Reviewed by: dev_submerge.ch, markj
Differential Revision: https://reviews.freebsd.org/D47459

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sound: Make device registration more intuitive

The way a sound driver currently registers to sound(4) is using the
following sequence of function calls:

1. pcm_register() to initialize snddev_info.

sound: Make device registration more intuitive

The way a sound driver currently registers to sound(4) is using the
following sequence of function calls:

1. pcm_register() to initialize snddev_info.
2. pcm_addchan() calls to create the device's primary channels.
3. pcm_setstatus() to do the final setup.

While using 3 different functions in a specific order might not be very
elegant, this pattern cannot be easily avoided. However, pcm_register()
and pcm_setstatus() are especially confusing, since one would
intuitively expect:

1. pcm_register() to actually do the registration, as opposed to a basic
initialization.
2. pcm_setstatus() to, as the name suggests, set some kind of status, as
opposed to finalizing the registration.

This patch renames pcm_register() to pcm_init(), and pcm_setstatus() to
pcm_register(). Drivers are modified accordingly.

Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Reviewed by: dev_submerge.ch
Differential Revision: https://reviews.freebsd.org/D47325

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snd_dummy: Drain callout during detach

If we do not enter dummy_chan_trigger() before detaching, we'll get a
use-after-free since the callout(9) callback might be called after
having been detached.

snd_dummy: Drain callout during detach

If we do not enter dummy_chan_trigger() before detaching, we'll get a
use-after-free since the callout(9) callback might be called after
having been detached.

Sponsored by: The FreeBSD Foundation
MFC after: 2 days
Reviewed by: dev_submerge.ch, markj, emaste
Differential Revision: https://reviews.freebsd.org/D46715

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sound: Implement dummy driver

Sponsored by: The FreeBSD Foundation
MFC after: 2 days
Reviewed by: dev_submerge.ch
Differential Revision: https://reviews.freebsd.org/D45967