[Bug 220986] MediaTek MT7925 Bluetooth adapter (USB 13d3:3596) fails to initialize - reports as unsupported hardware variant 0x7902

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=220986

--- Comment #3 from Alex (aamolodc@gmail.com) ---
additional context:

## What I've Tested (2026-01-21)

**1. Applied the USB ID blacklist fixes:**
- Installed libmtp-1.1.22-2.fc43.x86_64 (includes 13d3:3596 blacklist)
- Installed libgphoto2-2.5.33-1.fc43.x86_64 (includes 13d3:3596 blacklist)

**2. Performed full cold boot:**
- Shut down completely (not reboot)
- Unplugged power cable for 30+ seconds to clear hardware state
- Booted directly to Linux (did not boot Windows first)

**3. Verified Windows functionality:**
- Rebooted to Windows 11
- Bluetooth works perfectly (can pair devices, transfer files, etc.)
- This confirms the hardware itself is not defective

**4. Returned to Linux:**
- Bluetooth still fails with the same error

## Current Behavior in Linux

Bluetooth fails immediately at boot, before any desktop environment loads:

```
[   19.247336] Bluetooth: hci0: Opcode 0x0c03 failed: -110
```

Technical details:
- USB device is detected: `Bus 001 Device 003: ID 13d3:3596 IMC Networks
Wireless_Device`
- btusb driver binds to the device correctly
- hci0 device is created in `/sys/class/bluetooth/`
- Firmware file exists:
`/lib/firmware/mediatek/mt7925/BT_RAM_CODE_MT7925_1_1_hdr.bin`
- **Problem:** HCI_Reset command times out (error -110 = ETIMEDOUT)
- The chip does not respond to any HCI commands from the Linux driver
- Firmware loading is never attempted because the driver fails before that
stage

## Why This Is Different From Bug #220682

**Bug #220682 (USB ID 0489:e111):**
- Bluetooth worked after boot
- Failed only after user logged into GNOME desktop
- Caused by libmtp/libgphoto2 probing the device during desktop startup
- **Fixed** by blacklisting the USB ID in libmtp/libgphoto2

**This bug #220986 (USB ID 13d3:3596):**
- Bluetooth never works, not even for a moment
- Fails at boot time, before any desktop environment starts
- Fails even with libmtp/libgphoto2 blacklists applied
- **Not fixed** by the package updates

## Root Cause

There are TWO separate issues affecting USB ID 13d3:3596:

1. **USB ID conflict** (shared with bug #220682) - RESOLVED by package updates
2. **Kernel driver initialization failure** (unique to this bug) - UNRESOLVED

The btusb driver cannot communicate with the MT7925 chip at the hardware level.
Since the same hardware works perfectly in Windows, this indicates the Linux
driver is missing vendor-specific initialization code or using an incorrect
initialization sequence for this particular chip variant.

## Why Hardware Defect Is Ruled Out

- Device works perfectly in Windows 11 (Bluetooth pairs, connects, transfers
data)
- WiFi portion of the same combo card works in Linux (mt7925 driver)
- USB device is detected and enumerated correctly in Linux
- This is a software/driver issue, not hardware

## Request

Please reopen this bug as a kernel driver issue. The libmtp/libgphoto2 fixes
from bug #220682 are necessary but not sufficient to make this device work.

**System Information:**
- OS: Fedora Linux 43 (Workstation Edition)
- Kernel: 6.18.5-200.fc43.x86_64
- Hardware: MediaTek MT7925 Bluetooth/WiFi combo (Filogic 310)
- USB ID: 13d3:3596 (IMC Networks)
- Subsystem: AzureWave 6040
- Motherboard: ASUS TUF GAMING B650M-E WIFI

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