Yocto Build Linux

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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.

1 Toolchain installation for out of Yocto builds

To install the toolchain, follow Yocto Toolchain installation.

2 Build Linux out of Yocto tree

Get the Linux source code:

$ git clone https://github.com/varigit/linux-imx.git
$ cd linux-imx
$ git checkout imx_4.14.98_2.0.0_ga_var01

Build the Linux kernel:

$ source /opt/fsl-imx-xwayland/4.14-sumo/environment-setup-aarch64-poky-linux
$ unset LDFLAGS
$ make mrproper
$ make imx8_var_defconfig
Customize the kernel configuration (optional step):
$ make menuconfig
Build everything:
$ make -j4
Build Image.gz only:
$ make -j4  Image.gz

Build modules only:
$ make -j4  modules

Build device trees only:
$ make -j4 dtbs
Build only the device tree for VAR-SOM-MX8X WIFI configuration:
$ make -j4 freescale/fsl-imx8qxp-var-som-wifi.dtb

Build only the device tree for VAR-SOM-MX8X SD configuration:
$ make -j4 freescale/fsl-imx8qxp-var-som-sd.dtb


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.

3 Install the built kernel 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/rootfs:

Install the kernel image and modules:
$ kver=$(strings arch/arm64/boot/Image | grep -i "Linux version" | awk '{print $3}')
$ sudo cp arch/arm64/boot/Image.gz /media/user/rootfs/boot/Image.gz-${kver}
$ sudo ln -fs /boot/Image.gz-${kver} /media/user/rootfs/boot/Image.gz
$ sudo make ARCH=arm64 modules_install INSTALL_MOD_PATH=/media/user/rootfs

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