Building the MT7921 WiFi Driver on OSMC (Raspberry Pi 4)

Mar 5, 2026 — A complete guide to backporting and building the MT7921 WiFi driver on OSMC's Raspberry Pi 4, where the mixed-architecture setup and older kernel make it anything but straightforward. — 10 minutes read

Due to my housing arrangements, my Raspberry Pi 4 was left without Ethernet access. The Pi 4 does have a built-in WiFi chip (Broadcom BCM43455, 802.11ac), but it’s single-stream — in practice you get around 80–115 Mbps. That’s not enough when you want to stream media and download at the same time through OSMC.

So I ended up acquiring a Fenvi FU-AX1800 USB WiFi adapter, which uses the MediaTek MT7921au chipset and supports WiFi 6 with 2x2 MIMO — a significant upgrade. But plugging it in revealed a different problem entirely.

The MT7921 is supported by the mt7921u kernel driver — but that driver was only added in kernel 5.18. OSMC ships with kernel 5.15, so the driver simply isn’t there.

I’ve backported the driver from 5.18.19, but building it on OSMC is not a straightforward make && make install for two reasons:

OSMC uses a mixed-architecture setup. The Raspberry Pi 4 runs a 64-bit (aarch64) kernel but OSMC’s userland is 32-bit (armhf). All system tools — including gcc from apt — are 32-bit and cannot compile 64-bit kernel modules. You need an aarch64 cross-compiler, and OSMC’s cross-compiler package ships inside a chroot that requires wrapper scripts to use.
The kernel source tree needs manual preparation. OSMC doesn’t set up the /lib/modules/<version>/build symlink or copy the kernel .config by default, so the out-of-tree module build will fail unless you wire these up yourself and run modules_prepare first.

The steps below walk through the full process — from installing the toolchain to connecting to WiFi.

Environment

Device: Raspberry Pi 4 running OSMC
Kernel: 5.15.92-1-osmc (aarch64 kernel, armhf userland)
USB Adapter: Fenvi FU-AX1800 (MediaTek MT7921au, USB ID 0e8d:7961)

Step 1: Install build dependencies

sudo apt update
sudo apt install -y build-essential git libssl-dev bc file

If libssl-dev fails with a 404, download manually:

wget http://security.debian.org/debian-security/pool/updates/main/o/openssl/libssl1.1_1.1.1w-0+deb11u4_armhf.deb -O /tmp/libssl1.1.deb
wget http://security.debian.org/debian-security/pool/updates/main/o/openssl/libssl-dev_1.1.1w-0+deb11u4_armhf.deb -O /tmp/libssl-dev.deb
sudo dpkg -i /tmp/libssl1.1.deb /tmp/libssl-dev.deb

Step 2: Install kernel headers and source

Out-of-tree module builds need the kernel headers and source to compile against. OSMC packages these separately.

sudo apt install -y rbp464-headers-sanitised-5.15.92-1-osmc rbp464-source-5.15.92-1-osmc

Note: Use apt-cache search rbp464 if the exact version has changed.

Step 3: Create the kernel build symlink

The kernel build system expects the source tree at /lib/modules/<version>/build, but OSMC doesn’t create this symlink automatically.

sudo ln -sf /usr/src/rbp464-source-5.15.92-1-osmc /lib/modules/5.15.92-1-osmc/build

Step 4: Install the cross-compiler

The kernel is arm64 but userland is armhf, so a cross-compiler is needed:

sudo apt install -y aarch64-toolchain-osmc

This installs a chroot-based toolchain at /opt/osmc-tc/aarch64-toolchain-osmc/.

Step 5: Set up cross-compiler wrapper scripts

The OSMC toolchain is packaged inside a chroot, so the binaries can’t find their dynamic linker and shared libraries when called directly from the host. Wrapper scripts set the correct LD_LIBRARY_PATH so the 64-bit compiler tools work outside the chroot.

# Create the dynamic linker symlink
sudo ln -sf /opt/osmc-tc/aarch64-toolchain-osmc/lib/ld-linux-aarch64.so.1 /lib/ld-linux-aarch64.so.1

# Create wrapper scripts
sudo mkdir -p /usr/local/aarch64-cross
for tool in $(ls /opt/osmc-tc/aarch64-toolchain-osmc/usr/bin/aarch64-linux-gnu-* | xargs -n1 basename); do
  sudo tee /usr/local/aarch64-cross/$tool > /dev/null <<SCRIPT
#!/bin/sh
export LD_LIBRARY_PATH=/opt/osmc-tc/aarch64-toolchain-osmc/lib/aarch64-linux-gnu:/opt/osmc-tc/aarch64-toolchain-osmc/usr/lib/aarch64-linux-gnu
export PATH=/usr/local/aarch64-cross:\$PATH
exec /opt/osmc-tc/aarch64-toolchain-osmc/usr/bin/$tool "\$@"
SCRIPT
  sudo chmod +x /usr/local/aarch64-cross/$tool
done

Step 6: Create assembler symlinks for GCC

When GCC invokes the assembler or linker internally, it looks for unprefixed tool names (as, ld, etc.) in <sysroot>/usr/aarch64-linux-gnu/bin/. The OSMC toolchain doesn’t populate this directory, so GCC fails with “unknown assembler invoked”. These symlinks fix that.

sudo mkdir -p /opt/osmc-tc/aarch64-toolchain-osmc/usr/aarch64-linux-gnu/bin
for tool in as ar ld ld.bfd ld.gold nm objcopy objdump ranlib readelf strip; do
  sudo ln -sf /opt/osmc-tc/aarch64-toolchain-osmc/usr/bin/aarch64-linux-gnu-$tool \
    /opt/osmc-tc/aarch64-toolchain-osmc/usr/aarch64-linux-gnu/bin/$tool
done

Step 7: Copy kernel config and prepare for module building

The kernel source tree needs the running kernel’s .config and a modules_prepare pass to generate the headers and scripts that out-of-tree builds depend on (e.g. Module.symvers, generated headers).

sudo cp /boot/config-5.15.92-1-osmc /usr/src/rbp464-source-5.15.92-1-osmc/.config

export LD_LIBRARY_PATH=/opt/osmc-tc/aarch64-toolchain-osmc/lib/aarch64-linux-gnu:/opt/osmc-tc/aarch64-toolchain-osmc/usr/lib/aarch64-linux-gnu

sudo -E make -C /usr/src/rbp464-source-5.15.92-1-osmc \
  ARCH=arm64 \
  CROSS_COMPILE=/usr/local/aarch64-cross/aarch64-linux-gnu- \
  modules_prepare

Note: Ignore the libarmmem.so preload warnings — they are harmless (32-bit library being skipped by 64-bit processes).

Step 8: Install firmware files

The MT7921 chipset requires firmware blobs that the driver uploads to the device at load time. OSMC’s kernel 5.15 doesn’t ship these since it has no built-in MT7921 support. Download them from the upstream linux-firmware repository.

sudo mkdir -p /lib/firmware/mediatek

sudo wget -O /lib/firmware/mediatek/WIFI_MT7961_patch_mcu_1_2_hdr.bin \
  https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/plain/mediatek/WIFI_MT7961_patch_mcu_1_2_hdr.bin

sudo wget -O /lib/firmware/mediatek/WIFI_RAM_CODE_MT7961_1.bin \
  https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/plain/mediatek/WIFI_RAM_CODE_MT7961_1.bin

Step 9: Clone and build the mt7921 driver

cd ~
git clone https://github.com/tomhudak/mt7921.git
cd mt7921

export LD_LIBRARY_PATH=/opt/osmc-tc/aarch64-toolchain-osmc/lib/aarch64-linux-gnu:/opt/osmc-tc/aarch64-toolchain-osmc/usr/lib/aarch64-linux-gnu

make ARCH=arm64 \
  CROSS_COMPILE=/usr/local/aarch64-cross/aarch64-linux-gnu- \
  CONFIG_MT76_CONNAC_LIB=m \
  CONFIG_MT7921_COMMON=m \
  CONFIG_MT7921U=m

Critical: You must pass CONFIG_MT76_CONNAC_LIB=m on the make command line. The kernel .config doesn’t include this option, and without it the mt76-connac-lib.ko module won’t be built, causing “Unknown symbol” errors when loading.

Step 10: Install the modules

sudo -E make ARCH=arm64 \
  CROSS_COMPILE=/usr/local/aarch64-cross/aarch64-linux-gnu- \
  CONFIG_MT76_CONNAC_LIB=m \
  CONFIG_MT7921_COMMON=m \
  CONFIG_MT7921U=m \
  modules_install

The cp: -r not specified errors at the end are harmless (firmware directory copy issue in the install script). The .ko modules are installed correctly.

Run depmod manually (it gets skipped due to missing System.map):

sudo /sbin/depmod -a

Step 11: Load the driver

sudo /sbin/modprobe mt7921u

Verify the adapter appears:

ip link show
# You should see wlan1 (or similar)

dmesg | grep mt7921
# Should show: "mt7921u 1-1.3:1.0: HW/SW Version: ..."
# And: "WM Firmware Version: ..."

Step 12: Configure autoload on boot

Without this, you’d have to manually modprobe mt7921u after every reboot.

echo 'mt7921u' | sudo tee /etc/modules-load.d/mt7921u.conf

Step 13: Connect to WiFi

OSMC uses connman (not NetworkManager) for network management. A provisioning file tells connman how to connect to your network automatically.

sudo tee /var/lib/connman/your-wifi.config > /dev/null <<'EOF'
[service_your_wifi]
Type=wifi
Name=YOUR_SSID
Security=psk
Passphrase=YOUR_PASSWORD
AutoConnect=true
IPv4=dhcp
EOF

Then restart connman and connect:

sudo systemctl restart connman
connmanctl scan wifi
connmanctl services
# Find your network's service ID for wlan1 (identified by the MAC address)
connmanctl connect wifi_XXXX_YYYY_managed_psk

Troubleshooting

Problem	Solution
`/lib/modules/.../build` not found	Redo step 3 (symlink)
`unknown assembler invoked` during modules_prepare	Redo step 6 (assembler symlinks for GCC)
`__uint128_t` error	Make sure you’re using `ARCH=arm64` with the aarch64 cross-compiler
`bc: not found` during modules_prepare	`sudo apt install bc`
`Unknown symbol mt76_connac_*` when loading	Rebuild with `CONFIG_MT76_CONNAC_LIB=m` (step 9)
`Not registered` when connecting via connmanctl	Create a provisioning file (step 13) or restart connman
`libarmmem.so` preload warnings	Harmless — 32-bit library being skipped by 64-bit processes
Module doesn’t load after reboot	Check `/etc/modules-load.d/mt7921u.conf` exists (step 12)

Built modules reference

The following kernel modules are installed in /lib/modules/5.15.92-1-osmc/updates/:

Module	Purpose
`mt76/mt76.ko`	Core mt76 driver
`mt76/mt76-usb.ko`	mt76 USB transport
`mt76/mt76-connac-lib.ko`	mt76 connectivity library (MCU/MAC)
`mt76/mt7921/mt7921-common.ko`	MT7921 common driver
`mt76/mt7921/mt7921u.ko`	MT7921 USB driver (loads all deps)

The source code for the backported driver is available at github.com/tomhudak/mt7921.