Modify, rebuild and reload the Linux® kernel

1 Overview

This stage explains how modify, rebuild and reload the Linux® kernel.
You will first be guided to install the Linux® kernel source code in the Developer Package directory. Then step by step you will execute procedures to modify, rebuild and reload the Linux® kernel.

2 Download the the Linux® kernel source code

The software package is provided AS IS, and by downloading it, you agree to be bound to the terms of the software license agreement (SLA0048). The detailed content licenses can be found here.

• Download the [unknown revision /unknown revision STM32MP15-Ecosystem-v3.0.0 Developer Package Sources] to the following directory:
  $HOME/STM32MPU_workspace/STM32MP15-Ecosystem-v3.0.0/Developer-Package
• Uncompress the tarball file to get the Linux® kernel tarball, the ST patches and the ST configuration fragments

 cd $HOME/STM32MPU_workspace/STM32MP15-Ecosystem-v3.0.0/Developer-Package
 tar xvf unknown revision 

3 Prepare the Linux® kernel source code

• Extract the Linux® kernel source

 cd unknown revision 
 tar xvf unknown revision 

• Apply the ST patches

 cd unknown revision 
 for p in `ls -1 ../*.patch`; do patch -p1 < $p; done

• Apply fragments

 make ARCH=arm multi_v7_defconfig "fragment*.config"
 for f in `ls -1 ../fragment*.config`; do scripts/kconfig/merge_config.sh -m -r .config $f; done
 yes '' | make ARCH=arm oldconfig

4 Build the Linux® kernel source code for the first time

Information

The first time the kernel is build it could take several minutes.

• Build kernel images (uImage and vmlinux) and device tree (dtbs)

 make ARCH=arm uImage vmlinux dtbs LOADADDR=0xC2000040

• Build kernel module

 make ARCH=arm modules

• Generate output build artifacts

 mkdir -p $PWD/install_artifact/
 make ARCH=arm INSTALL_MOD_PATH="$PWD/install_artifact" modules_install

5 Deploy the Linux® kernel on the board

5.1 Push the Linux® kernel into the board

 scp arch/arm/boot/uImage root@<board ip address>:/boot

5.2 Push the devicetree into the board

 scp arch/arm/boot/dts/stm32mp157*.dtb root@<board ip address>:/boot

5.3 Push the kernel modules into the board

• Remove the link created inside the install_artifact/lib/modules/<kernel version> directory

 rm install_artifact/lib/modules/5.10.10/build install_artifact/lib/modules/5.10.10/source 

• Optionally, strip kernel modules (to reduce the size of each kernel modules)

 find install_artifact/ -name "*.ko" | xargs $STRIP --strip-debug --remove-section=.comment --remove-section=.note --preserve-dates

• Copy Kernel modules

 scp -r install_artifact/lib/modules/* root@<ip of board>:/lib/modules

• Using the Linux console, re-generate the list of module dependencies (modules.dep) and the list of symbols provided by modules (modules.symbols)

 /sbin/depmod -a

• Synchronize data on disk with memory

 sync

5.4 Reboot the board

 reboot

6 Modifying a built-in Linux kernel device driver

This simple example adds unconditional log information when the display driver is probed.

• Using the Linux console, check that there is no log information when the display driver is probed

 dmesg | grep -i stm_drm_platform_probe

• Go to the Linux® kernel source directory

 cd $HOME/STM32MPU_workspace/STM32MP15-Ecosystem-v3.0.0/Developer-Package/unknown revision /unknown revision 

• Edit the ./drivers/gpu/drm/stm/drv.c source file
• Add a log information in the stm_drm_platform_probe function as follow

static int stm_drm_platform_probe(struct platform_device *pdev)
{
	struct device *dev = &pdev->dev;
	struct drm_device *ddev;
	int ret;
	[...]

	DRM_INFO("Simple example - %s\n", __func__);

	return 0;
	[...]
}

• Save the file
• Rebuitd the Linux® kernel

 make uImage LOADADDR=0xC2000040

• Update the Linux kernel image into board

 scp arch/arm/boot/uImage root@<board ip address>:/boot

• Reboot the board

 reboot

• Check that there is now log information when the display driver is probed

 dmesg | grep -i stm_drm_platform_probe
[    2.764080] [drm] Simple example - stm_drm_platform_probe