[Bug] Audio Regression on Ubuntu 26.04 LTS (J413): UCM Path Broken & Speaker Locked

[3h-young-tea]

[Bug] Audio Regression on Ubuntu 26.04 LTS (J413): UCM Path Broken & Speaker Locked

asahi-diagnose-20260428-104533.txt

Description

Following the official release of Ubuntu 26.04 LTS, the built-in speakers on the MacBook Air M2 (J413) have stopped functioning. While this hardware worked on previous versions (25.10), the new LTS release appears to have a broken audio configuration path, causing the hardware safety driver to lock the volume at -100dB.

System Information

• Hardware: MacBook Air M2 (J413)
• OS: Ubuntu 26.04 LTS (Official Release, April 2026)
• Kernel: 6.17.0-1001-asahi-arm
• Audio Stack: PipeWire 1.6.2 / WirePlumber 1.6.2
• Regression: Confirmed. Audio was functional on Ubuntu 25.10.

Diagnostic Evidence

1. UCM Configuration Failure (The Root Cause)

The ALSA Use Case Manager cannot find or import the specific configuration for the J413 hardware. Running alsaucm returns a "No such file" error despite the hardware being detected:

$ alsaucm listcards
ALSA lib main.c:1804:(snd_use_case_mgr_open) [error.ucm] failed to import hw:0 use case configuration -2

Note: The directory /usr/share/alsa/ucm2/conf.d/apple/ is missing in the 26.04 installation.

2. Kernel Hardware Safety Lock

Because the UCM fails to initialize the routing and limits, the snd-soc-macaudio driver enters a safety lock state to protect the speakers, resulting in a permanent -100dB gain:

[74293.774941] snd-soc-macaudio sound: Speaker volumes locked: Lock timeout

3. PipeWire Node Mismatch

Without the UCM profile, PipeWire falls back to a generic stereo node which is incompatible with the M2's 4-speaker DSP requirements:

• Node: alsa_output.platform-sound.stereo-fallback
• Status: Shows as [vol: 0.32 MUTED] and cannot be unmuted effectively.

Steps to Reproduce

1. Install/Upgrade to Ubuntu 26.04 LTS on MacBook Air M2.
2. Observe that the speaker sink exists but produces no sound.
3. Verify the -100dB limit in amixer -c 0.

Attempted Workarounds

• Manually symlinking /usr/share/asahi-audio/j413 to /usr/share/alsa/ucm2/conf.d/apple/j413.
• Restarting pipewire and speakersafetyd.
• Result: Failed. The alsaucm error persists, suggesting the new ALSA version in 26.04 might be looking for a different directory structure or requires updated UCM syntax.

Expected Behavior

The asahi-audio configurations should be correctly linked during the upgrade/installation process, allowing speakersafetyd to unlock the volume and PipeWire to use the correct j413 audio profile.

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Diagnostic Log: asahi-diagnose-20260428-104533.txt attached.