Modify, rebuild and reload the Linux® kernel

Applicable for STM32MP25x lines

Develop on Arm® Cortex®-A35 Develop on Arm® Cortex®-M33
Step category in.png Install the SDK Step.png Create a simple hello-world application Step.png Modify, rebuild and reload the Linux® kernel Step category out.png

1. Overview[edit source]

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[edit source]

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-6.1-yocto-mickledore-mpu-v24.06.26.tar.gz for STM32MP257F-EV1 More info green.png boards.

  • Download and install the STM32MPU OpenSTLinux BSP package.
STM32MPU Developer Package - STM32MPU ecosystem v5.1.0 release
  • Go on to download the STM32MP2 Developer Package, en.sources-stm32mp2-openstlinux-6.1-yocto-mickledore-mpu-v24.06.26.tar.gz file.
cd <working directory path>/Developer-Package
tar xvf en.sources-stm32mp2-openstlinux-6.1-yocto-mickledore-mpu-v24.06.26.tar.gz
Release note

Details about the content of the OpenSTLinux BSP package are available in the associated STM32 MPU OpenSTLinux release note.

Archive box.png For information on older releases, go to Archives.

 cd stm32mp2-openstlinux-6.1-yocto-mickledore-mpu-v24.06.26/sources/aarch64-ostl-linux/linux-stm32mp-6.1.82-stm32mp-r2-r0

3. Prepare the Linux® kernel source code[edit source]

Extract the Linux® kernel source

 tar xvf linux-6.1.82.tar.xz

Apply ST patches

 cd linux-6.1.82
 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/ -m -r -O ${OUTPUT_BUILD_DIR} ${OUTPUT_BUILD_DIR}/.config $f; done
 yes '' |  make oldconfig O="${OUTPUT_BUILD_DIR}"

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

Info white.png 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[edit source]

5.1. Push the Linux® kernel and the devicetree onto the board[edit source]

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

5.2. Push the kernel modules onto the board[edit source]

  • Remove the link created inside the install_artifact/lib/modules/<kernel version> directory
 rm install_artifact/lib/modules/6.1.82/build install_artifact/lib/modules/6.1.82/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

5.3. Reboot the board[edit source]


6. Modify a built-in Linux® kernel device driver[edit source]

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/STM32MPU-Ecosystem-v5.1.0/Developer-Package/stm32mp2-openstlinux-6.1-yocto-mickledore-mpu-v24.06.26/sources/aarch64-ostl-linux/linux-stm32mp-6.1.82-stm32mp-r2-r0/linux-6.1.82

  • 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
  • Update the Linux kernel image into board
 scp ${OUTPUT_BUILD_DIR}/arch/${ARCH}/boot/${IMAGE_KERNEL} root@<board ip address>:/boot
  • Reboot the board
  • 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

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