Building the 5.4 Kernel for PICO-IMX8M-MINI

Introduction

This article will take you through the steps of building the Linux kernel for the PICO-IMX8M-MINI.

Download and setup a cross toolchain

If you haven't already done so, you will need download and setup a cross toolchain for a 64-bit ARM target SOC.

Clone the Linux kernel git repository and checkout the 5.4 branch:

    $ git clone https://github.com/TechNexion/linux-tn-imx.git
    $ git checkout tn-imx_5.4.47_2.2.0-next

Configure the kernel to build for the 64-bit i.MX8 target:

    $ make tn_imx8_defconfig

Build the kernel:

    $ make -j$(nproc)

The resulting binary image file is located in arch/arm64/boot/Image .

Locate the device tree blobs:

By default the following device tree blobs (binaries) are located in arch/arm64/boot/dts/freescale .

Specify DTB to be loaded in kernel

The DTB must be loaded into memory prior to kernel boot. This is done with U-boot. You specify the DTB file to be loaded in an environment variable in U-boot that is named fdt_file. U-boot then scans the boot partition (a FAT partition) for a file of that name. If it finds this file, it will load it into the prescribed memory to location prior to loading and booting the kernel.

You can list the DTB files available in the boot partition using the fatls command. First, you can figure out which is the correct boot device using the mmc list command:

    u-boot=> mmc list
    FSL_SDHC: 1
    FSL_SDHC: 2 (eMMC)

Assuming we are booting from e.MMC, the mmc device is 2.

Then run the fatls command:

    u-boot=> fatls mmc 2
     23715848   Image
         6320   hello_world.bin
        51947   imx8mm-pico-pi-ili9881c.dtb
        54429   imx8mm-pico-pi-voicehat.dtb
        51425   imx8mm-pico-pi.dtb
        16888   rpmsg_lite_pingpong_rtos_linux_remote.bin
        16520   rpmsg_lite_str_echo_rtos_imxcm4.bin
       209878   splash.bmp

Then, you can set the environment variable fdt_file to the DTB of your choice:

    u-boot=> setenv fdt_file imx8mm-pico-pi-ili9881c.dtb
    u-boot=> saveenv