sound: Fix min/max sample rate assignment for VCHANs

[christos]

Summary

Currently the min/max sample rate reported for a given VCHAN is whatever
is specified in dev.pcm.X.[play|rec].vchanrate, and is the same for both
the min and the max. For example, if *.vchanrate is set to 48000, then
the min/max will be both 48000. Fix this by assigning the min/max to
either the physical channel's min/max, or, when hw.snd.feeder_rate_round
is set to 0, to feeder_rate_[min|max].

Sponsored by: The FreeBSD Foundation
MFC after: 2 days

Test Plan

Printing the oss_audioinfo->[min|max]_rate for a VCHAN when hw.snd.feeder_rate_round is not 0:

min_rate=44100
max_rate=96000

Which is the min/max of the physical channel.

And with hw.snd.feeder_rate_round=0:

min_rate=1
max_rate=2016000

Which takes the value from feeder_rate_[min|max]:

root@freebsd:~ # sysctl hw.snd.feeder_rate_min
hw.snd.feeder_rate_min: 1
root@freebsd:~ # sysctl hw.snd.feeder_rate_max
hw.snd.feeder_rate_max: 2016000

[christos]

sys/dev/sound/pcm/vchan.c

216

@dev_submerge.ch I am not really sure what values we must assign in the case of AFMT_PASSTHROUGH. Any ideas?

[dev_submerge.ch]

sys/dev/sound/pcm/vchan.c

216

The passthrough formats I know are all 48kHz on optical / SPDIF, but I think HDMI audio has more options now. This is supposedly going out bitperfect with no sample rate conversion, which suggests these should match the physical sample rates of the hardware.

[christos]

sys/dev/sound/pcm/vchan.c

216

Then I can assign them to the parent channel's min/max as I do in the !feeder_rate_round case (will add appropriate AFMT_PASSTHROUGH check to make sure we never end up in the feeder_rate_round case for passthrough vchans).

[christos]

Handle AFMT_PASSTHROUGH case: Set min/max to the parent's min/max.

[christos]

Any comments?

[dev_submerge.ch]

Sorry for the delay, had some serious outage due to virus infection (me, not my machines). Just to make sure, this is for the SNDCTL_ENGINEINFO case, right?

There's another thing to check here, with > 8 channels we set the bitperfect flag on the parent channel, and sample rate conversion is not possible to my knowledge. That case is similar but separate from AFMT_PASSTHROUGH, see the check in sys/dev/sound/pcm/feeder_chain.c:

/*
   * If channel is in bitperfect or passthrough mode, make it appear
   * that 'origin' and 'target' identical, skipping mostly chain
   * procedures.
   */
  if (CHN_BITPERFECT(c) || (c->format & AFMT_PASSTHROUGH)) {

AFAIK, current convention is for drivers to set the bitperfect flag when channel count exceeds 8 outputs / inputs. At least snd_uaudio and the snd_hdsp* drivers do so. There's also the possibility to set the bitperfect sysctl for pcm devices, but I'm not sure how that affects vchans.

[dev_submerge.ch]

sys/dev/sound/pcm/vchan.c

227–228

I get a panic here when running ossinfo, it says "mutex not owned", at sys/dev/sound/pcm/channel.c:2409. The vchan_getcaps() function is called from dsp_oss_audioinfo().