Bug#1136889: linux-image-6.12.88+deb13-amd64: Bluetooth broken after upgrade to 6.12.88

Source: linux
Version: 6.12.88+deb13-amd64
Followup-For: Bug #1136889
X-Debbugs-Cc: [email protected], [email protected]
User: [email protected]
Usertags: amd64

Dear Maintainer,

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-- System Information:
Debian Release: 13.5
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 6.12.74+deb13+1-amd64 (SMP w/12 CPU threads; PREEMPT)
Kernel taint flags: TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=pl_PL.UTF-8, LC_CTYPE=pl_PL.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled


Same issue reproduced here.

Hardware:
HP ProBook 465 G11
MediaTek MT7921 Bluetooth/Wi-Fi

Broken kernel:
6.12.88+deb13-amd64

Working kernel:
6.12.74+deb13+1-amd64

Symptoms:

* bluetoothctl: "No default controller available"
* btmgmt info: "Index list with 0 items"

Relevant dmesg output:
Bluetooth: hci0: Failed to send wmt func ctrl (-22)

Issue disappears completely after booting older kernel.

Firmware packages installed:

* firmware-mediatek
* firmware-linux
* firmware-linux-nonfree
* firmware-misc-nonfree

Troubleshooting attempted:

* restart bluetooth.service
* reload btusb/btmtk modules
* full poweroff
* unplugging USB hub/peripherals

Regression reproducible consistently on 6.12.88 only.