# working when running as root
# install build requirements
apt install -y git bc bison flex libssl-dev make libncurses5-dev
# clone and download kernel sources
cd /opt
git clone --depth=1 https://github.com/raspberrypi/linux
cd linux

# create kernel config
#RASPI 4: `make bcm2711_defconfig`
#RASPI 5: `make bcm2712_defconfig`

# # DO OTHER TUNINGS HERE via `make menuconfig`

# set PG table size to 4 instead of default 3
sed -i 's/CONFIG_PGTABLE_LEVELS=3/CONFIG_PGTABLE_LEVELS=4/' .config

# compile (requires a lot of time on raspi 4)
make -j4 Image.gz modules dtbs
make modules_install

# copy compiled resources
cp arch/arm64/boot/dts/broadcom/*.dtb /boot/
cp arch/arm64/boot/dts/overlays/*.dtb* /boot/overlays/
cp arch/arm64/boot/dts/overlays/README /boot/overlays/
# RASPI 4: cp arch/arm64/boot/Image.gz /boot/kernel8.img
# RASPI 5: cp arch/arm64/boot/Image.gz /boot/firmware/kernel8.img

# use new kernel
echo "kernel=kernel8.img" | tee -a /boot/config.txt

reboot