Modify, rebuild and reload the Linux® kernel



1. Overview[edit | 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 | edit source]

STM32MP1 Developer Package - OpenSTLinux BSP

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

 cd unknown revision

Extract the Linux® kernel source

 tar xvf unknown revision

Apply 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[edit | edit source]

  • 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[edit | edit source]

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

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

5.2. Push the devicetree into the board[edit | edit source]

 scp arch/arm/boot/dts/stm32mp1xx*.dtb root@<board ip address>:/boot

5.3. Push the kernel modules onto the board[edit | edit source]

  • 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[edit | edit source]

 reboot

6. Modify a built-in Linux® kernel device driver[edit | 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/STM32MP1-Ecosystem-v4.0.0/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 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