[REQUEST] Bluetooth firmware via usbipd

[4-FLOSS-Free-Libre-Open-Source-Software]

Kernel missing Bluetooth device drivers to turn on Bluetooth USB adapter device.
CONFIG_BT_RTL=y: Bluetooth device drivers

zcat /proc/config.gz | grep CONFIG_BT_RTL
zcat /proc/config.gz | grep CONFIG_BT_HCIBTUSB
# CONFIG_BT_HCIBTUSB is not set
zcat /proc/config.gz | grep CONFIG_RFKILL
# CONFIG_RFKILL is not set

RFKILL may be required to power on the chip

rfkill list
rfkill: /dev/rfkill not found...

• Enable Bluetooth support #82

This other custom WSL kernel seems to have Bluetooth support: https://github.com/dathpo/wsl2-linux-kernel?tab=readme-ov-file#readme-fork

[4-FLOSS-Free-Libre-Open-Source-Software]

Still no luck with Bluetooth

sudo journalctl --follow --identifier=bluetoothd
bluetoothd[78957]: Bluetooth daemon 5.72
bluetoothd[78957]: Starting SDP server
bluetoothd[78957]: src/plugin.c:plugin_init() System does not support csip plugin
bluetoothd[78957]: profiles/audio/micp.c:micp_init() D-Bus experimental not enabled
bluetoothd[78957]: src/plugin.c:plugin_init() System does not support micp plugin
bluetoothd[78957]: src/plugin.c:plugin_init() System does not support vcp plugin
bluetoothd[78957]: src/plugin.c:plugin_init() System does not support mcp plugin
bluetoothd[78957]: src/plugin.c:plugin_init() System does not support bass plugin
bluetoothd[78957]: src/plugin.c:plugin_init() System does not support bap plugin
bluetoothd[78957]: profiles/network/bnep.c:bnep_init() kernel lacks bnep-protocol support
bluetoothd[78957]: src/plugin.c:plugin_init() System does not support network plugin
bluetoothd[78957]: src/rfkill.c:rfkill_init() Failed to open RFKILL control device
bluetoothd[78957]: Bluetooth management interface 1.23 initialized

[4-FLOSS-Free-Libre-Open-Source-Software]

I don't know much about this driver related stuff,
could it be made compatible just by flipping some kernel flags ?

sudo journalctl --follow --identifier=bluetoothd
wsl bluetoothd[163919]: profiles/audio/micp.c:micp_init() D-Bus experimental not enabled
wsl bluetoothd[163919]: src/plugin.c:plugin_init() System does not support micp plugin
wsl bluetoothd[163919]: src/plugin.c:plugin_init() System does not support vcp plugin
wsl bluetoothd[163919]: src/plugin.c:plugin_init() System does not support mcp plugin
wsl bluetoothd[163919]: src/plugin.c:plugin_init() System does not support bass plugin
wsl bluetoothd[163919]: src/plugin.c:plugin_init() System does not support bap plugin
wsl bluetoothd[163919]: profiles/network/bnep.c:bnep_init() kernel lacks bnep-protocol support
wsl bluetoothd[163919]: src/plugin.c:plugin_init() System does not support network plugin
wsl bluetoothd[163919]: src/rfkill.c:rfkill_init() Failed to open RFKILL control device
wsl bluetoothd[163919]: Bluetooth management interface 1.23 initialized

Perhaps those needed?

CONFIG_BT_HCIBTUSB=m
CONFIG_BT_HCIBTUSB_RTL=y 

For bluez?

CONFIG_BT_BNEP=m
CONFIG_BT_BNEP_MC_FILTER=y
CONFIG_BT_BNEP_PROTO_FILTER=y

bluetooth low energy?

CONFIG_BT_LE=y
CONFIG_BT_BREDR=y

[4-FLOSS-Free-Libre-Open-Source-Software]

Kernel missing Bluetooth device drivers to turn on Bluetooth USB adapter device. CONFIG_BT_RTL=y: Bluetooth device drivers

zcat /proc/config.gz | grep CONFIG_BT_RTL
zcat /proc/config.gz | grep CONFIG_BT_HCIBTUSB

CONFIG_BT_HCIBTUSB is not set

zcat /proc/config.gz | grep CONFIG_RFKILL

CONFIG_RFKILL is not set

in 6.18.3 things changed:

CONFIG_BT_RTL=m
CONFIG_BT_HCIBTUSB=m
CONFIG_BT_HCIBTUSB_AUTOSUSPEND=y
CONFIG_BT_HCIBTUSB_POLL_SYNC=y
CONFIG_BT_HCIBTUSB_BCM=y
CONFIG_BT_HCIBTUSB_MTK=y
CONFIG_BT_HCIBTUSB_RTL=y
# CONFIG_RFKILL is not set

Perhaps CONFIG_RFKILL still missing part of puzzle Bluetooth device drivers?

[4-FLOSS-Free-Libre-Open-Source-Software]

Probably fixed by USB network drivers from

• [Config] Sync MAIN/LTS configs with Microsoft 6.18 kernel #154

will recheck later again with the newest kernel

[4-FLOSS-Free-Libre-Open-Source-Software]

RTL8761BU Bluetooth firmware not found via usbipd on WSL2 kernel 6.18.30-locietta-WSL2-xanmod1

Please consider embedding the Realtek RTL8761BU firmware into the WSL2 kernel build

Environment

Linux wsl2 6.18.30-locietta-WSL2-xanmod1 #1 SMP PREEMPT_DYNAMIC Fri May 15 03:05:42 UTC 2026 x86_64 x86_64 x86_64 GNU/Linux

Problem

The adapter is passed through successfully from Windows to WSL2 via usbipd. lsusb sees the device and btusb binds to both interfaces, but no usable Bluetooth controller is created.

btmgmt info stays empty:

Index list with 0 items

Relevant dmesg:

Bluetooth: hci0: RTL: examining hci_ver=0a hci_rev=000b lmp_ver=0a lmp_subver=8761
Bluetooth: hci0: RTL: loading rtl_bt/rtl8761bu_fw.bin
bluetooth hci0: Direct firmware load for rtl_bt/rtl8761bu_fw.bin failed with error -2
Bluetooth: hci0: RTL: firmware file rtl_bt/rtl8761bu_fw not found

Firmware files exist

/usr/lib/firmware/rtl_bt/rtl8761bu_fw.bin
/usr/lib/firmware/rtl_bt/rtl8761bu_config.bin

SHA256:

1d7a9597349ad89344fa16c1913d3e39e9a12e966e417ca16871bc79bbe59edb  rtl8761bu_fw.bin
6c28a3f07c6a30ed208c4b64862a23f02b7d93543ea980edd24df16bab45095f  rtl8761bu_config.bin

zgrep --extended-regexp \
  'CONFIG_FW_LOADER=|CONFIG_EXTRA_FIRMWARE=|CONFIG_EXTRA_FIRMWARE_DIR=|CONFIG_FW_LOADER_USER_HELPER|CONFIG_BT_RTL|CONFIG_BT_HCIBTUSB' \
  /proc/config.gz

Current kernel config
CONFIG_BT_RTL=m
CONFIG_BT_HCIBTUSB=m
CONFIG_BT_HCIBTUSB_RTL=y
CONFIG_FW_LOADER=y
CONFIG_EXTRA_FIRMWARE=""
# CONFIG_FW_LOADER_USER_HELPER is not set

Setting runtime firmware path did not fix it:

printf '%s' '/usr/lib/firmware' | sudo tee /sys/module/firmware_class/parameters/path >/dev/null

The firmware load still fails with error -2.
ONFIG_EXTRA_FIRMWARE="rtl_bt/rtl8761bu_fw.bin rtl_bt/rtl8761bu_config.bin"
CONFIG_EXTRA_FIRMWARE_DIR="/usr/lib/firmware"

Expected result: btusb can initialize the Realtek RTL8761BU adapter via usbipd-win, btmgmt info shows a hci0 controller, and BlueZ can use the adapter.