btusb-13d3-3625-dkms

DKMS module that adds USB device 13d3:3625 (IMC Networks / MediaTek MT7922) to the Linux btusb driver with the correct BTUSB_MEDIATEK | BTUSB_WIDEBAND_SPEECH flags.

Why

The device 13d3:3625 is not yet in the upstream kernel's btusb device table. Without a matching entry, the driver won't use the MediaTek-specific initialization path and the Bluetooth adapter won't work.

This module patches btusb.c at build time instead of bundling a full copy, so it stays compatible across kernel updates.

How it works

1. pre_build.sh fetches btusb.c and its local headers from the local kernel tree or, if unavailable (e.g. Arch/CachyOS), downloads them from kernel.org for the target kernel version.
2. If 13d3:3625 is already present in the source (merged upstream), the patch is skipped automatically.
3. Otherwise, it applies a unified patch (--fuzz=0). If the context doesn't match the kernel version, a perl fallback inserts the entry after the /* MediaTek MT7922 Bluetooth devices */ comment.
4. The patched btusb.ko is compiled out-of-tree and installed to /updates/dkms/, which takes priority over the in-tree module.

Install

# Copy source to /usr/src
sudo cp -r btusb-13d3-3625-1.0 /usr/src/

# Register and install
sudo dkms add btusb-13d3-3625/1.0
sudo dkms install btusb-13d3-3625/1.0

# Reload the module
sudo modprobe -r btusb && sudo modprobe btusb

Verify

# DKMS status
dkms status | grep btusb

# Confirm the DKMS module is loaded (not the in-tree one)
modinfo btusb | grep filename
# Expected: /lib/modules/.../updates/dkms/btusb.ko.zst

Uninstall

sudo dkms remove btusb-13d3-3625/1.0 --all
sudo rm -rf /usr/src/btusb-13d3-3625-1.0

Files

File	Purpose
dkms.conf	DKMS configuration
pre_build.sh	Fetches sources, applies patch, handles fallback
patches/0001-btusb-add-13d3-3625.patch	Unified diff adding the device entry

Notes

• Tested on CachyOS (Arch-based) with kernel 6.18.x.
• On Arch, kernel headers don't include driver .c files, so pre_build.sh downloads them from kernel.org. An internet connection is required during the first build for each kernel version.
• AUTOINSTALL="yes" ensures automatic rebuild on kernel upgrades via the DKMS pacman hook.
• Once 13d3:3625 lands upstream, the module will detect it and skip patching — no manual intervention needed.

License

The patch modifies GPL-licensed kernel code (drivers/bluetooth/btusb.c). This project is distributed under the same GPL-2.0 license.