Modify, rebuild and reload the Linux® kernel

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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

2.1. For STM32MP1 series

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.

• The OpenSTLinux BSP package is delivered through a tarball file named en.SOURCES-stm32mp1-openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06.tar.gz for STM32MP157x-EV1 , STM32MP157x-DKx and STM32MP135x-DK boards.

• Download and install the STM32MP1 OpenSTLinux BSP package.

	STM32MP1 Developer Package - STM32MP1 ecosystem v6.0.0 release
Download	Go on st.com to download the STM32MP1 Developer Package, en.SOURCES-stm32mp1-openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06.tar.gz file.
Installation	Go to the host PC directory where you extracted the package from the .jar file if you follow the proposition to organize the working directory, that is: cd <working directory path>/Developer-Package tar xvf en.SOURCES-stm32mp1-openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06.tar.gz
Release note	Details about the content of the OpenSTLinux BSP package are available in the associated STM32 MPU OpenSTLinux release note. For information on older releases, go to Archives.

cd stm32mp1-openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06/sources/arm-ostl-linux-gnueabi/linux-stm32mp-6.6.48-stm32mp-r1-r0

2.2. For STM32MP2 series

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.

• The OpenSTLinux BSP package is delivered through a tarball file named en.SOURCES-stm32mp2-openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06.tar.gz for STM32MP257F-EV1 and STM32MP257F-DK boards.

• Download and install the STM32MPU OpenSTLinux BSP package.

	STM32MPU Developer Package - STM32MPU ecosystem v6.0.0 release
Download	Go on st.com to download the STM32MP2 Developer Package, en.SOURCES-stm32mp2-openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06.tar.gz file.
Installation	Go to the host PC directory where you extracted the package from the .jar file if you follow the proposition to organize the working directory, that is: cd <working directory path>/Developer-Package tar xvf en.SOURCES-stm32mp2-openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06.tar.gz
Release note	Details about the content of the OpenSTLinux BSP package are available in the associated STM32 MPU OpenSTLinux release note. For information on older releases, go to Archives.

cd stm32mp2-openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06/sources/aarch64-ostl-linux/linux-stm32mp-6.6.48-stm32mp-r1-r0

3. Prepare the Linux^® kernel source code

Extract the Linux^® kernel source

tar xvf linux-6.6.48.tar.xz

Apply ST patches

cd linux-6.6.48
for p in `ls -1 ../*.patch`; do patch -p1 < $p; done

• Configure build directory

export OUTPUT_BUILD_DIR=$PWD/../build
mkdir -p ${OUTPUT_BUILD_DIR}

• Apply fragments

make O="${OUTPUT_BUILD_DIR}" defconfig fragment*.config
for f in `ls -1 ../fragment*.config`; do scripts/kconfig/merge_config.sh -m -r -O ${OUTPUT_BUILD_DIR} ${OUTPUT_BUILD_DIR}/.config $f; done
(yes '' || true) |  make oldconfig O="${OUTPUT_BUILD_DIR}"

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

Information

Building the kernel for the first time can take several minutes.

• Select which kind of image to build regarding the SDK installed

[ "${ARCH}" = "arm" ] && imgtarget="uImage" || imgtarget="Image.gz"
export IMAGE_KERNEL=${imgtarget}

• Build kernel images ([uImage|Image.gz] and vmlinux) and device tree (dtbs)

make ${IMAGE_KERNEL} vmlinux dtbs LOADADDR=0xC2000040 O="${OUTPUT_BUILD_DIR}"

• Build kernel module

make modules O="${OUTPUT_BUILD_DIR}"

• Generate output build artifacts

make INSTALL_MOD_PATH="${OUTPUT_BUILD_DIR}/install_artifact" modules_install O="${OUTPUT_BUILD_DIR}"
mkdir -p ${OUTPUT_BUILD_DIR}/install_artifact/boot/
cp ${OUTPUT_BUILD_DIR}/arch/${ARCH}/boot/${IMAGE_KERNEL} ${OUTPUT_BUILD_DIR}/install_artifact/boot/
find ${OUTPUT_BUILD_DIR}/arch/${ARCH}/boot/dts/ -name 'st*.dtb' -exec cp '{}' ${OUTPUT_BUILD_DIR}/install_artifact/boot/ \;

5. Deploy the Linux^® kernel on the board

5.1. Push the Linux^® kernel and the devicetree onto the board

cd ${OUTPUT_BUILD_DIR}/install_artifact
scp -r boot/* root@<ip of board>:/boot/

5.2. Push the kernel modules onto the board

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

rm lib/modules/6.6.48/build

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

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

• Copy kernel modules

scp -r 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

5.3. 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

For STM32MP1 series

cd $HOME/STM32MPU_workspace/STM32MPU-Ecosystem-v6.0.0/Developer-Package/stm32mp1-openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06/sources/arm-ostl-linux-gnueabi/linux-stm32mp-6.6.48-stm32mp-r1-r0/linux-6.6.48

For STM32MP2 series

cd $HOME/STM32MPU_workspace/STM32MPU-Ecosystem-v6.0.0/Developer-Package/stm32mp2-openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06/sources/aarch64-ostl-linux/linux-stm32mp-6.6.48-stm32mp-r1-r0/linux-6.6.48

---

• 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 ${IMAGE_KERNEL} LOADADDR=0xC2000040 O="${OUTPUT_BUILD_DIR}"

• Update the Linux kernel image into board

scp ${OUTPUT_BUILD_DIR}/arch/${ARCH}/boot/${IMAGE_KERNEL} 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

Linux^® is a registered trademark of Linus Torvalds.

Board support package

Software development kit (A programming package that enables a programmer to develop applications for a specific platform.)c

Direct rendering manager (kernel module that gives direct hardware access to DRI clients, find more information on official DRI web site http://dri.freedesktop.org/wiki/DRM)

Linux^® is a registered trademark of Linus Torvalds.

Board support package

Software development kit (A programming package that enables a programmer to develop applications for a specific platform.)c

Direct rendering manager (kernel module that gives direct hardware access to DRI clients, find more information on official DRI web site http://dri.freedesktop.org/wiki/DRM)

Direct rendering infrastructure (Linux^® framework for allowing direct access to graphics hardware... find more information on official DRI web site http://dri.freedesktop.org/)