[PATCH 0/3] ALSA: 6fire: S/PDIF output

["Piotr Gliźniewicz" <p.glizniewicz@gmail.com>]

The DMX 6Fire USB has a coaxial S/PDIF output, which the driver keeps
disabled. This series enables it as playback channels 7 and 8 of the
existing PCM device, the layout chosen in the RFC thread [1].

Patch 1 takes stream_mutex in the "Digital Thru Playback Route" put.
It fixes a race with prepare that exists in mainline, and patch 3
depends on the lock.

Patch 2 adds a playback channel map in the order of the manual of the
card, FL FR FC LFE RL RR on Line Out 1 to 6.

Patch 3 adds the output with the "IEC958 Playback Default", "IEC958
Playback Con Mask" and "IEC958 Playback Switch" controls. With 8
channels the card runs at 96 kHz at most. The Pro Audio profile of
PipeWire 1.6.9 opened the device with 8 channels, so with this series
it gets 8 channels at up to 96 kHz instead of 6 channels at up to
192 kHz. A client that asks for 6 channels still gets 176.4 and
192 kHz.

A UCM profile for alsa-ucm-conf will describe the channels: the default
variant with analog 5.1 and S/PDIF as two sinks at up to 96 kHz, and a
"HiFi Analog" variant with analog 5.1 only at up to 192 kHz, which
turns the switch off while in use. I tested a draft with
PipeWire 1.6.9 and this series; I will send it after the kernel
patches are accepted.

[1] https://lore.kernel.org/linux-sound/30dcedc7-3b56-4396-af3d-6c2701ef1cb7@perex.cz/

Piotr Gliźniewicz (3):
  ALSA: 6fire: take stream_mutex in the Digital Thru control
  ALSA: 6fire: add a playback channel map
  ALSA: 6fire: add S/PDIF output

 sound/usb/6fire/control.c |  32 +++-
 sound/usb/6fire/pcm.c     | 334 ++++++++++++++++++++++++++++++++++++--
 sound/usb/6fire/pcm.h     |   7 +-
 3 files changed, 351 insertions(+), 22 deletions(-)

-- 
2.56.0