Compiling Linux Kernel 5.4.x LTS for Acqua

This article illustrates how to generate a bootable Linux Kernel image for Acqua SOM starting from the Linux Kernel sources available on the The Linux Kernel Archives

Prerequisite

A Linux PC in required to cross compile the Kernel image.

This procedure has been tested on:

Ubuntu 18.04.4 LTS (amd64)
Debian Buster 10 (amd64)

Follow this article to install the Toolchain requested to compile the sources:

Install the ARM cross compiler toolchain on your Linux PC

Moving from the Kernel 4.19 to 5.4 it is requested to compile the at91bootstrap bootloader following this guide:

https://www.acmesystems.it/at91bootstrap

The previous version of at91bootstrap 3.9.1 will not work correctly

It is advisable to have a Debug Port Interface like DPI or USB-3V-SER to check the error messages during the Kernel bootstrap

Step-by-step procedure

Open a terminal on your Linux PC and download the Linux Kernel sources from the main stream repository:

wget https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.4.163.tar.xz

extract the Kernel sources from the compressed file by typing:

tar xvfJ linux-5.4.163.tar.xz

move inside the folder created:

cd linux-5.4.163

copy the basic kernel defconfig file suggested from us

wget https://www.acmesystems.it/www/acqua_compile_kernel_5_4/acme-acqua_defconfig -O arch/arm/configs/acme-acqua_defconfig

Set the defconfig:

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- acme-acqua_defconfig

Customize the default Linux Kernel configuration:

If you need to customize the Kernel configuration or you just want to take a look around the Kernel setup type:

make ARCH=arm menuconfig

and navigate inside the Kernel configuration using the arrow keys and following the help provided by the menuconfig interface.

Note to use the 7 inch display on the legacy BERTA-A5 display boards

If you are using a TFT with your Acme board change the file

drivers/gpu/drm/panel/panel-simple.c

using these commands:

rm drivers/gpu/drm/panel/panel-simple.c
wget https://www.acmesystems.it/www/acqua_compile_kernel_5_4/panel-simple.c -O drivers/gpu/drm/panel/panel-simple.c

Generate the Device Tree Blob file (.dtb)

Download the Acqua device tree file:

wget https://www.acmesystems.it/www/acqua_compile_kernel_5_4/at91-sama5d3_acqua.dts -O arch/arm/boot/dts/at91-sama5d3_acqua.dts

Now compile the device tree file:

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- at91-sama5d3_acqua.dtb

Compile the Kernel image

Compile the Linux Kernel sources and generate the binary compressed image file to save in the first partition of microSD card.

make -j8 ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- zImage
...
Image arch/arm/boot/zImage is ready

Compile the Kernel modules

The image generated contains the Linux Kernel and all the built-in device drivers (option [*] in menuconfig) compiled with it.

Al the drivers compiled as external modules (option [M] in menuconfig) need to be compiled and saved in the rootfs /lib directory on the second partition of the microSD. We didn't use any [M] flag in our defconfig so this procedure is not requested but. in case you add something. these are the commands to use to compile them:

make modules -j8 ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-
make modules_install INSTALL_MOD_PATH=./modules ARCH=arm

Copy the boot files into the first microSD partition

Insert a formatted microSD with the boot loader (at91bootstrap) and the rootfs contents already created in your Linux PC and copy on it these files:

Write the Linux Kernel image and the device tree blob in the first microSD partition:

sudo cp arch/arm/boot/zImage /media/$USER/boot
sudo cp arch/arm/boot/dts/at91-sama5d3_acqua.dtb /media/$USER/boot/at91-sama5d3_acqua.dtb

Write the Linux Kernel modules inside the second microSD partition:

sudo rsync -avc modules/lib/. /media/$USER/rootfs/lib/.

After the first boot

At the first access to the board command line update the module dependencies by typing this command:

depmod -a

Create a defconfig of your own Kernel configuration

make ARCH=arm savedefconfig

The file defconfig contains your configuration. You could rename and copy it in arch/arm/configs/

cp defconfig arch/arm/configs/my_defconfig

Links

Kernel configuration (acme-acqua_defconfig)
Device tree (at91-sama5d3_acqua.dts)
Kernel source changed:
- drivers/gpu/drm/panel/panel-simple.c

Sergio Tanzilli
Systems designer, webmaster of www.acmesystems.it and founder of Acme Systems srl

Personal email: tanzilli@acmesystems.it
Web pages: https://www.acmesystems.it --- https://www.acmestudio.it
Github repositories: https://github.com/tanzilli --- https://github.com/acmesystems
Telegram group dedicated to the Acme Systems boards: https://t.me/acmesystemssrl

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