t2bce_audio regression on MacBookAir8,1 since linux-t2 7.1.5: page fault in t2audio_pcm_open

[roy-devx]

t2bce_audio regression on MacBookAir8,1 since linux-t2 7.1.5: page fault in t2audio_pcm_open

Hardware

• Model: MacBook Air 2018 (MacBookAir8,1)
• DMI: Apple Inc. MacBookAir8,1 / Mac-827FAC58A8FDFA22
• Distribution: Arch Linux
• Audio: Apple T2 Audio

Problem

Internal T2 audio works correctly with linux-t2 7.1.4-2, but is broken with both:

• linux-t2 7.1.5-1
• linux-t2 7.1.6-1

With 7.1.5/7.1.6, WirePlumber hangs while opening the T2 audio PCM device. wpctl status hangs indefinitely and pactl times out.

Downgrading back to linux-t2 7.1.4-2 immediately restores normal audio functionality.

I tested upgrading and downgrading more than once and the behavior follows the kernel version.

Kernel command line

BOOT_IMAGE=/vmlinuz-linux-t2 root=UUID=<redacted> rw intel_iommu=on iommu=pt pm_async=off loglevel=3

Working kernel: 7.1.4-2

$ uname -r
7.1.4-arch1-Watanare-T2-2-t2

wpctl status works normally:

Audio
 ├─ Devices:
 │      50. Apple Audio Device                  [alsa]
 │      51. Internal Audio                      [alsa]
 │
 ├─ Sinks:
 │  *   58. Apple Audio Device Speakers
 │      59. Apple Audio Device Headphones
 │
 ├─ Sources:
 │  *   60. Apple Audio Device BuiltinMic
 │      61. Apple Audio Device HeadsetMic

WirePlumber is also in a normal sleeping state:

$ ps -o pid,state,wchan:32,comm -C wireplumber
PID  S  WCHAN                             COMMAND
1875 S  poll_schedule_timeout.constprop.  wireplumber

ALSA exposes the Speaker PCM correctly:

card: 0
device: 0
subdevice: 0
stream: PLAYBACK
id: Speaker
name: Speaker
subname: subdevice #0
subdevices_count: 1
subdevices_avail: 1

Broken kernel: 7.1.6-1

$ uname -r
7.1.6-arch1-Watanare-T2-1-t2

During initialization t2bce_audio reports:

t2bce_audio: Subdevice not found for BufferStruct device Speaker
t2bce_audio: Subdevice not found for BufferStruct device Codec Output
t2bce_audio: Subdevice not found for BufferStruct device Digital Mic
t2bce_audio: Subdevice not found for BufferStruct device Codec Input
t2bce_audio: Subdevice not found for BufferStruct device Speaker@mcpl\x04

A few seconds later the kernel reports a page fault when WirePlumber attempts to open the PCM device:

#PF: error_code(0x0000) - not-present page
CPU: 0 PID: 745 Comm: wireplumber
Hardware name: Apple Inc. MacBookAir8,1/Mac-827FAC58A8FDFA22
RIP: 0010:t2audio_pcm_open+0x48/0x110 [t2bce_audio]

Relevant stack:

t2audio_pcm_open+0x48/0x110 [t2bce_audio]
snd_pcm_open_substream
snd_pcm_open
snd_pcm_playback_open
do_sys_openat2

After this happens, WirePlumber becomes stuck in uninterruptible sleep:

PID   S  WCHAN                            COMMAND
1826  D  snd_pcm_substream_proc_status_re wireplumber

It cannot be terminated normally, and system shutdown/reboot takes a very long time.

ALSA behavior on 7.1.6

The Apple T2 card itself is detected:

0 [Audio]: - Apple T2 Audio
             Apple T2 Audio
1 [PCH]: HDA-Intel - HDA Intel PCH

However, aplay -l only gets as far as:

card 0: Audio [Apple T2 Audio], device 4: Bridge Loopback [Bridge Loopback]

and then hangs. Even Ctrl+C does not return to the shell.

The device nodes do exist, including:

pcmC0D100c
pcmC0D101p
pcmC0D102p
pcmC0D103c
pcmC0D4c
pcmC0D4p

but /proc/asound/card0/pcm0p/info, which exists and works on 7.1.4, is not present on 7.1.6.

PipeWire symptoms

After the failure:

$ pactl info
Connection failure: Timeout

$ pactl list short sinks
Connection failure: Timeout

wpctl status hangs indefinitely.

pavucontrol remains at:

Establishing connection to PulseAudio. Please wait...

On some boots audio output may initially work, but the PipeWire/WirePlumber control interface still becomes unresponsive.

Regression

The behavior appears to be:

linux-t2 7.1.4-2
    -> works normally

linux-t2 7.1.5-1
    -> broken

downgrade to 7.1.4-2
    -> works normally again

upgrade to 7.1.5-1
    -> broken again

linux-t2 7.1.6-1
    -> still broken

downgrade to 7.1.4-2
    -> works normally again

This looks like a regression in t2bce_audio, possibly related to the mapping/initialization of the audio BufferStruct subdevices.

The page fault in t2audio_pcm_open() appears to occur after the driver has already reported that the Speaker/Codec/Mic BufferStruct subdevices could not be found.

The complete dmesg output from the affected 7.1.6 boot is attached below.

貼り付けられたテキスト（1 点）(20260809-213602).txt