sound: Bail out early if a format is not supported

[christos]

Summary

If a format is unsupported, the feeder_build_* functions will fail
anyway, so bail out early to avoid unnecessary computation.

This is also needed by a series of upcoming patches to the feeder
framework.

Sponsored by: The FreeBSD Foundation
MFC after: 2 days

[christos]

sys/dev/sound/pcm/feeder_chain.c

712

Maybe ENODEV would be better.

[dev_submerge.ch]

sys/dev/sound/pcm/feeder_chain.c

578–579

This seems redundant with AFMT_CONVERTIBLE from sound.h?

706–712

Below we handle *any* format with bitperfect / passthrough. If these cases never hit feeder_chain() then the code below is superfluous, but I suspect it's not. Which means we cannot bail out early here?

[christos]

sys/dev/sound/pcm/feeder_chain.c

578–579

I am aware of it, but I thought the "convertible" part in the name would make the meaning of the operation non-obvious. I can however, use AFMT_CONVERTIBLE and add a comment, which should be fine.

706–712

That's a good point. I think the check could be moved to the else (non-bitperfect/non-passthrough) case instead.

[christos]

• Use AFMT_CONVERTIBLE.
• Move check inside non-bitperfect/passthrough case.

[christos]

Bump.

[christos]

Rebase.

[christos]

Bump.

[christos]

Bump.