[Bug 221539] New: MT7925 Bluetooth fails to initialize since kernel 7.0.8 — regression from 7.0.5

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=221539

            Bug ID: 221539
           Summary: MT7925 Bluetooth fails to initialize since kernel
                    7.0.8 — regression from 7.0.5
           Product: Drivers
           Version: 2.5
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: Bluetooth
          Assignee: linux-bluetooth@vger.kernel.org
          Reporter: sphinx-rift-sector@duck.com
        Regression: No

**Hardware:**
- Framework Laptop 13 (AMD AI 300 series)
- WiFi/BT chip: MediaTek MT7925 (RZ717)
- PCIe ID: MEDIATEK Corp. MT7925 (RZ717) Wi-Fi 7 160MHz
- BT interface: USB (hci0)

**Working kernel:** 7.0.5
**Broken kernel:** 7.0.8
**Firmware:** linux-firmware 20260410
(mediatek/mt7925/BT_RAM_CODE_MT7925_1_1_hdr.bin)
**Distro:** NixOS 26.05 (unstable)

**Description:**

Bluetooth on the MediaTek MT7925 stopped working after upgrading the kernel
from 7.0.5 to 7.0.8. WiFi continues to work via the mt7925e PCIe driver. The BT
USB device enumerates and hci0 is created, but the WMT firmware handshake fails
with EINVAL (-22). The adapter cannot be brought up.

This is a regression: the same firmware and hardware work on kernel 7.0.5.

**Symptoms:**

- `hciconfig hci0` shows BD Address: 00:00:00:00:00:00, state DOWN
- `hciconfig hci0 up` returns: "Can't init device hci0: Invalid argument (22)"
- `modprobe -r btusb && modprobe btusb` does not resolve the issue
- Rebooting does not resolve the issue
- rfkill shows hci0 not blocked (soft or hard)

**dmesg (relevant lines):**

```
Bluetooth: Core ver 2.22
Bluetooth: HCI device and connection manager initialized
Bluetooth: HCI socket layer initialized
Bluetooth: L2CAP socket layer initialized
Bluetooth: SCO socket layer initialized
usbcore: registered new interface driver btusb
Bluetooth: hci0: HW/SW Version: 0x00000000, Build Time: 20260106153314
Bluetooth: hci0: Failed to send wmt func ctrl (-22)
Bluetooth: hci0: HCI Enhanced Setup Synchronous Connection command is
advertised, but not supported.
mt7925e 0000:c0:00.0: WM Firmware Version: ____000000, Build Time:
20260106153120
```

Note: `HW/SW Version: 0x00000000` indicates the chip is not responding to
version queries during the WMT protocol handshake.

**Steps to reproduce:**

1. Boot a system with MediaTek MT7925 on kernel 7.0.8
2. Check `hciconfig hci0` — adapter is DOWN with null BD address
3. Attempt `hciconfig hci0 up` — fails with EINVAL
4. Downgrade to kernel 7.0.5 — Bluetooth works

**Related:**
- Bug 219sp688 reports MT7925 BT initialization failures on kernels 6.12–6.15,
but with USB enumeration timeouts (-110). This bug is different: USB
enumeration succeeds, but the WMT func ctrl command fails (-22).

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