conf: USB-Audio: use PCM device 1 for IEC958 on C-Media HIFI Decode Audio

conf: USB-Audio: use PCM device 1 for IEC958 on C-Media HIFI Decode Audio

[GitHub pull_request - opened]

alsa-project/alsa-lib pull request #534 was opened from bpkroth:

The C-Media "HIFI Decode Audio" USB device (`0d8c:0089`) puts its optical S/PDIF output on PCM device 1, but `USB-Audio.conf` maps `iec958` to device 0 unless the card is listed in `USB-Audio.pcm.iec958_device`.
As a result, the "Digital Stereo (IEC958)" output in PipeWire/PulseAudio plays through the analog jack and the optical output stays silent.

`/proc/asound/cardN/stream*` on this device:

- `stream0` (interface 1, PCM device 0): S16/S24/S32 plus DSD, 44.1 to 768 kHz. This is the analog DAC.
- `stream1` (interface 2, PCM device 1): S16/S24, 44.1 to 192 kHz. This is the optical S/PDIF output.
- `stream2` (interface 2, altset 3, PCM device 2): the non-PCM alternate setting of the same S/PDIF endpoint.

Tested on Ubuntu 26.04 (alsa-lib 1.2.15.3, PipeWire 1.6.2, kernel 7.0).
`speaker-test -D plughw:CARD=Audio,DEV=1` plays through the optical output.
With the same entry in `~/.asoundrc`, the PipeWire IEC958 sink plays through optical too.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Request URL   : https://github.com/alsa-project/alsa-lib/pull/534
Patch URL     : https://github.com/alsa-project/alsa-lib/pull/534.patch
Repository URL: https://github.com/alsa-project/alsa-lib