# Regression in 1.2.16: ALC4080 S/PDIF device dropped on MSI X870 Tomahawk (`0db0:cd0e`)

alsa-project/alsa-ucm-conf issue #773 was opened from CeaseFunction:

## Summary

After upgrading `alsa-ucm-conf` from `1.2.15.3` to `1.2.16`, the S/PDIF output device on my MSI X870 Tomahawk disappeared. The board matches the `Realtek/ALC4080` profile, and S/PDIF previously worked fine. Reverting **only** `alsa-ucm-conf` to `1.2.15.3` (leaving `alsa-lib 1.2.16` in place) immediately restored it, which isolates the regression to the profile data — specifically a new conditional in `USB-Audio/Realtek/ALC4080-HiFi.conf` that drops the S/PDIF device on boards whose PCM subdevice naming the new probe fails to match.

## Environment

- **Distribution:** CachyOS (Arch-based), rolling
- **`alsa-ucm-conf` broken:** 1.2.16-1
- **`alsa-ucm-conf` working:** 1.2.15.3-2
- **`alsa-lib`:** 1.2.16 (NOT reverted — see below)
- **Board / device:** MSI X870 Tomahawk, USB-attached audio, ID `0db0:cd0e`
- **Matched profile:** `Realtek/ALC4080` (via `USB-Audio/USB-Audio.conf`)
- **Kernel:** 7.0.10-2-cachyos
- **Audio server:** PipeWire 1.6.6 / WirePlumber 0.5.14

## Symptom

The S/PDIF output is no longer enumerated. Analog outputs on the same card are unaffected, and a separate USB DAC is unaffected. The S/PDIF device returns when `alsa-ucm-conf` alone is downgraded to 1.2.15.3.

## Root cause

Device matching is unchanged between versions — `0db0:cd0e` matches the ALC4080 block in `USB-Audio/USB-Audio.conf` in both 1.2.15.3 and 1.2.16, confirmed by:

```
grep -rl "0db0:cd0e" /usr/share/alsa/ucm2/           # 1.2.15.3 -> USB-Audio.conf
grep -rl "0db0:cd0e" .../1.2.16/.../ucm2/            # 1.2.16   -> USB-Audio.conf
```

The regression is inside `USB-Audio/Realtek/ALC4080-HiFi.conf`. 1.2.16 refactored the `Define` block so PCM values hold only the subdevice index (e.g. `SpdifPCM "3"`) and each `SectionDevice` rebuilds the full path as `hw:${CardId},${var:SpdifPCM}`. As part of that refactor, the S/PDIF section gained a device-probe gate:

```
If.spdif_dev2 {
    Condition { Type RegexMatch; String "${CardComponents}"; Regex "USB(0b05:(1996|1a5[23c])|0db0:1feb)" }
    True.Define { SpdifName "S/PDIF Output"; SpdifPCM "2" }
    False.If.spdif_nodev {
        Condition {
            Type String
            Empty "$${find-device:type=pcm,stream=playback,field=subname,regex='Audio #3'}"
        }
        True.Define.SpdifName ""        # <-- drops S/PDIF device entirely
    }
}
```

In 1.2.15.3 there was no such probe for this path; S/PDIF was unconditionally defined at subdevice 3. On the X870 Tomahawk, the `find-device ... subname regex='Audio #3'` lookup evidently does not match the board's actual subdevice subname, so `SpdifName` is set to `""` and the device is removed.

## Hardware confirmation — the probe queries the wrong field

`cat /proc/asound/card5/pcm*p/info` shows the S/PDIF PCM exists in hardware (device 3) and reveals exactly why the probe fails:

```
device: 0
name: USB Audio
subname: subdevice #0
...
device: 3
name: USB Audio #3
subname: subdevice #0
subdevices_count: 1
subdevices_avail: 0
```

The S/PDIF device (device 3) is present and works under 1.2.15.3. The string `Audio #3` appears in the **`name`** field (`USB Audio #3`). But the 1.2.16 probe searches **`field=subname`**:

```
Empty "$${find-device:type=pcm,stream=playback,field=subname,regex='Audio #3'}"
```

Every subdevice's `subname` on this board is just `subdevice #0` — `Audio #3` never appears in any `subname`. So `find-device` always returns empty, `spdif_nodev` always fires, and S/PDIF is dropped, even though device 3 plainly exists. The probe is matching against the wrong field.

## Steps to reproduce

1. On a board matching `Realtek/ALC4080` (e.g. `0db0:cd0e`) with working S/PDIF under `alsa-ucm-conf 1.2.15.3`.
2. Upgrade `alsa-ucm-conf` to 1.2.16.
3. Restart the audio stack: `systemctl --user restart pipewire pipewire-pulse wireplumber`.
4. S/PDIF output is gone.

## Expected vs actual

- **Expected:** S/PDIF output remains enumerated, as in 1.2.15.3.
- **Actual:** S/PDIF device is removed because the new `spdif_nodev` probe evaluates to empty on this board.

## Suggested fix direction

The `spdif_nodev` probe queries `field=subname` but the discriminating string (`Audio #3`) lives in the device's `name` field, not `subname`. On this board every `subname` is `subdevice #0`, so the probe can never match and S/PDIF is always suppressed. The probe should query `field=name` instead:

```
Empty "$${find-device:type=pcm,stream=playback,field=name,regex='Audio #3'}"
```

This likely affects all ALC4080 boards that hit the `spdif_nodev` fallback rather than the whitelisted `spdif_dev2` IDs (`0b05:1996`, `0b05:1a5[23c]`, `0db0:1feb`). Worth confirming the field name against whichever board originally motivated the probe, so the fix doesn't merely move the breakage.

## Workaround

Downgrade `alsa-ucm-conf` to 1.2.15.3 (no need to downgrade `alsa-lib`).

Issue URL     : https://github.com/alsa-project/alsa-ucm-conf/issues/773
Repository URL: https://github.com/alsa-project/alsa-ucm-conf