Modify, rebuild and reload the Linux® kernel

Applicable for

STM32MP15x lines

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Develop on Arm® Cortex®-A7				Develop on Arm® Cortex®-M4
	Install the SDK		Create a simple hello-world application		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 you will execute step by step procedures to modify, rebuild and reload the Linux^® kernel.

2 Download OpenSTLinux BSP that includes the Linux^® kernel source code

• The OpenSTLinux BSP package is delivered through a tarball file named SOURCES-stm32mp1-openstlinux-5.15-yocto-kirkstone-mp1-v22.06.15.tar.xz for STM32MP157x-EV1 , STM32MP157x-DKx and STM32MP135x-DK boards.

• Download and install the STM32MP1 OpenSTLinux BSP package

	STM32MP1 Developer Package - STM32MP1-Ecosystem-v4.0.0 release
Download	You need to be logged on my.st.com before accessing the following link: SOURCES-stm32mp1-openstlinux-5.15-yocto-kirkstone-mp1-v22.06.15.tar.xz
Installation	Go to the host PC directory in which you extracted the package from .jar file; if you follow the proposition to organize the working directory, it means: cd <working directory path>/Developer-Package tar xvf SOURCES-stm32mp1-openstlinux-5.15-yocto-kirkstone-mp1-v22.06.15.tar.xz
Release note	Details about the content of the OpenSTLinux BSP package are available in the associated STM32 MPU OpenSTLinux release note. If you are interested in older releases, have a look into the section Archives.

3 Prepare the Linux^® kernel source code

 cd stm32mp1-openstlinux-5.15-yocto-kirkstone-mp1-v22.06.15/sources/arm-ostl-linux-gnueabi/linux-stm32mp-5.15.24-stm32mp1-r1-r0

Extract the Linux^® kernel source

 tar xvf linux-5.15.24.tar.xz

Apply ST patches

 cd linux-stm32mp-5.15.24-stm32mp1-r1-r0
 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

Building the kernel for the first time can 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 onto 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/stm32mp1xx*.dtb root@<board ip address>:/boot

5.3 Push the kernel modules onto the board

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

 rm install_artifact/lib/modules/5.15.24/build install_artifact/lib/modules/5.15.24/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, regenerate 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 Modify 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/STM32MP1-Ecosystem-v4.0.0/Developer-Package/stm32mp1-openstlinux-5.15-yocto-kirkstone-mp1-v22.06.15/sources/arm-ostl-linux-gnueabi/linux-stm32mp-5.15.24-stm32mp1-r1-r0/linux-stm32mp-5.15.24-stm32mp1-r1-r0

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

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
• Rebuild 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 log information is now present when the display driver is probed

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