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 (SLA). The detailed content licenses can be found here.

To download a package, it is recommended to be logged in to your "myst" account [1]. If, trying to download, you encounter a “403 error”, you could try to empty your browser cache to workaround the problem. We are working on the resolution of this problem. We apologize for this inconvenience

2.1. For ecosystem release v2.0.0

• Download the STM32MP15-Ecosystem-v2.0.0 Developer Package Sources to the following directory:
  $HOME/STM32MPU_workspace/STM32MP15-Ecosystem-v2.0.0/Developer-Package
• Uncompress the tarball file to get the Linux® kernel tarball, the ST patches and the ST configuration fragments

PC $> cd $HOME/STM32MPU_workspace/STM32MP15-Ecosystem-v2.0.0/Developer-Package
PC $> tar xvf en.SOURCES-kernel-stm32mp1-openstlinux-5-4-dunfell-mp1-20-06-24.tar.xz

3. Prepare the Linux® kernel source code

• Extract the Linux® kernel source

For ecosystem release v2.0.0 
PC $> cd stm32mp1-openstlinux-5.4-dunfell-mp1-20-06-24/sources/arm-ostl-linux-gnueabi/linux-stm32mp-5.4.31-r0
PC $> tar xvf linux-5.4.31.tar.xz

• Apply the ST patches

PC $> cd linux-5.4.31 /* For ecosystem release v2.0.0  */
PC $> for p in `ls -1 ../*.patch`; do patch -p1 < $p; done

• Apply fragments

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

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

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

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

PC $> make ARCH=arm uImage vmlinux dtbs LOADADDR=0xC2000040

• Build kernel module

PC $> make ARCH=arm modules

• Generate output build artifacts

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

5. Deploy the Linux® kernel on the board

5.1. Push the Linux® kernel into the board

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

5.2. Push the devicetree into the board

PC $> 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

For ecosystem release v2.0.0 :
PC $> rm install_artifact/lib/modules/5.4.31/build install_artifact/lib/modules/5.4.31/source

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

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

• Copy Kernel modules

PC $> 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)

Board $> /sbin/depmod -a

• Synchronize data on disk with memory

Board $> sync

5.4. Reboot the board

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

Board $> dmesg | grep -i stm_drm_platform_probe
Board $>

• Go to the Linux® kernel source directory

For ecosystem release v2.0.0 :
PC $> cd $HOME/STM32MPU_workspace/STM32MP15-Ecosystem-v2.0.0/Developer-Package/stm32mp1-openstlinux-5.4-dunfell-mp1-20-06-24/sources/arm-ostl-linux-gnueabi/linux-stm32mp-5.4.31-r0/linux-5.4.31

• 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

PC $> make uImage LOADADDR=0xC2000040

• Update the Linux kernel image into board

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

• Reboot the board

Board $> reboot

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

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