Build Linux from source code¶

It is recommended to build the kernel image using Yocto (see the Customizing the Linux kernel page) instead of using the direct method described in this page.
This is because some of the Yocto packages may depend on the kernel, like the WiFi module that is built from outside of the kernel source tree on some of the Yocto releases.

Toolchain installation for out of Yocto builds¶

To install the toolchain, follow the Yocto Toolchain installation guide.

Setup the environment:¶

Setup a working directory

$ export WORKDIR=~/imx8qxp-var-som-linux
$ mkdir ${WORKDIR}

Build Linux out of Yocto tree¶

Fetch source code:¶

$ cd $WORKDIR
$ git clone https://github.com/varigit/linux-imx -b lf-6.6.y_6.6.52-2.2.0_var01 linux-imx

Build Kernel, Modules, and DTBs:¶

Setup the environment:

$ source /opt/fsl-imx-xwayland/6.6-scarthgap/environment-setup-armv8a-poky-linux  
$ unset LDFLAGS

Clean and prepare the kernel:

$ cd ${WORKDIR}/
$ make mrproper
$ make imx8_var_defconfig

Customize the kernel configuration (optional step):
$ make menuconfig

Build kernel parts:

Build everything:
$ make -j$(nproc)

Build Image.gz only:
$ make -j$(nproc)  Image.gz

Build modules only:
$ make -j$(nproc)  modules

Build device trees only:
$ make -j$(nproc) dtbs

Install kernel modules to temporary directory¶

Create a temporary directory to install the modules:

Optional: delete any old installation from previous builds:
$ rm -rf $WORKDIR/rootfs

Create new directory:
$ mkdir -p $WORKDIR/rootfs

Install the modules to the temporary rootfs:

$ cd ${WORKDIR}/ && \
  make ARCH=arm64 \
    INSTALL_MOD_STRIP=1 \
    INSTALL_MOD_PATH=$WORKDIR/rootfs \
    modules_install

Notes:

If you replace the kernel image (Image.gz) on your system, you also need to reinstall the kernel modules, and vice versa.

If you just want to make a change in the device tree, you can compile and replace it without replacing the kernel image and modules.

Install the built kernel images, modules, and device trees on an SD card¶

Copy the Image.gz and device trees to the SD card boot partition, and install the modules in the SD card rootfs partition.
Assuming the rootfs partition is mounted on /media/user/root:

Install the kernel image and modules:
$ cd ${WORKDIR}/
$ kver=$(strings arch/arm64/boot/Image | grep -i "Linux version" | awk 'NR==1 {print $3}')
$ sudo cp arch/arm64/boot/Image.gz /media/user/root/boot/Image.gz-${kver}
$ sudo ln -fs Image.gz-${kver} /media/user/root/boot/Image.gz
$ sudo rsync -Kra $WORKDIR/rootfs/* /media/user/root

Install the device trees:
$ sudo cp arch/arm64/boot/dts/freescale/*imx*var*.dtb /media/user/root/boot/

Install the built kernel images, modules, and device trees using SSH on a running target¶

The example below uses ssh to install the kernel on a running device.

First, export a variable with the ip address of your target device:

$ export TARGET_IP=192.168.0.205

Then, copy the kernel image and device trees to the temporary directory, send them to the target using ssh, and install them with the correct user permissions:

$ mkdir -p $WORKDIR/rootfs/boot && \
  cp ${WORKDIR}//arch/arm64/boot/dts/freescale/*imx*var*.dtb $WORKDIR/rootfs/boot && \
  cp ${WORKDIR}//arch/arm64/boot/Image.gz $WORKDIR/rootfs/boot/ && \
  ssh root@${TARGET_IP} 'mkdir /tmp/rootfs' && \
  tar czf - -C $WORKDIR/rootfs . | ssh root@${TARGET_IP} 'tar xzf - -C /tmp/rootfs && \
  chown -R root:root /tmp/rootfs && cp -a /tmp/rootfs/boot/* /boot/ && cp -a /tmp/rootfs/lib/* /lib/ && \
  rm -r /tmp/rootfs'