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DART-MX8M - Customizing the Debian Linux kernel

This section describes how to build a new kernel configuration using menuconfig and deploy it.

Building a custom device tree

To build and install a custom device tree, add the filename to the variable G_LINUX_DTB of the machine-specific file.

We will demonstrate it here exemplarily with the VAR-SOM-MX8M-NANO, but the same applies also to other modules.
Assuming you have created a custom device tree arch/arm64/boot/dts/freescale/imx8mn-var-som-custom.dts, you can add this to the G_LINUX_DTB list

G_LINUX_DTB="freescale/imx8mn-var-som-symphony.dtb
	freescale/imx8mn-var-som-symphony-root.dtb
	freescale/imx8mn-var-som-symphony-m7.dtb
	freescale/imx8mn-var-som-symphony-legacy.dtb
	freescale/imx8mn-var-som-symphony-legacy-root.dtb
	freescale/imx8mn-var-som-symphony-legacy-m7.dtb
	freescale/imx8mn-var-som-inmate.dtb"

for example, at the end:

G_LINUX_DTB="freescale/imx8mn-var-som-symphony.dtb
	freescale/imx8mn-var-som-symphony-root.dtb
	freescale/imx8mn-var-som-symphony-m7.dtb
	freescale/imx8mn-var-som-symphony-legacy.dtb
	freescale/imx8mn-var-som-symphony-legacy-root.dtb
	freescale/imx8mn-var-som-symphony-legacy-m7.dtb
	freescale/imx8mn-var-som-inmate.dtb
	freescale/imx8mn-var-som-custom.dtb"

File: ~/debian_imx8mq-var-dart/variscite/imx8mn-var-som/imx8mn-var-som.sh

After running the build script:

sudo MACHINE=imx8mn-var-som ./var_make_debian.sh -c kernel

the custom device tree should appear in the output folder: ~/debian_imx8mq-var-dart/output/imx8mn-var-som-custom.dtb

Configuring the kernel

The default kernel configuration file used by Debian is part of the kernel source tree and is located at:

~/debian_imx8mq-var-dart/src/kernel/arch/arm64/configs/imx8_var_defconfig

Modifying the kernel configuration

To modify the kernel configuration (add/remove features and drivers) please follow the steps below:

$ cd ~/debian_imx8mq-var-dart/src/kernel
$ sudo make ARCH=arm64 mrproper
$ sudo make ARCH=arm64 imx8_var_defconfig
$ sudo make ARCH=arm64 menuconfig

Navigate the menu and select the desired kernel functionality

Exit the menu and answer "Yes" when asked "Do you wish to save your new configuration?"

$ sudo make ARCH=arm64 savedefconfig
$ sudo cp arch/arm64/configs/imx8_var_defconfig arch/arm64/configs/imx8_var_defconfig.orig
$ sudo cp defconfig arch/arm64/configs/imx8_var_defconfig

Building a new kernel configuration

Build the kernel image, dtb files and kernel modules

$ cd ~/debian_imx8mq-var-dart
$ sudo MACHINE=imx8mq-var-dart ./var_make_debian.sh -c kernel
$ sudo MACHINE=imx8mq-var-dart ./var_make_debian.sh -c modules
$ sudo MACHINE=imx8mq-var-dart ./var_make_debian.sh -c kernelheaders

Note: If you have modules newly added / removed, make sure you run the following command:

$ sudo MACHINE=imx8mq-var-dart ./var_make_debian.sh -c rtar

This will create a rootfs.tar.gz file that contains your new modules.

Deploy the kernel image, dtb files and kernel modules

Deploy Kernel, dtb via network

Updating Device tree to target

Transfer dtbs to target
On PC:

$ cd ~/debian_imx8mq-var-dart
$ scp output/*.dtb root@<yourboard-ip>:/boot/

Once prompted give root as password. <yourboard-ip> is ipaddress of your board.
Once transfer is done, follow below commands
On Target Console:

# sync;reboot

Note: If you just intend to do dtb, then only follow this section and reboot the target

Updating kernel Image to target

Transfer the output/zImage kernel image to target
On PC:

$ scp output/zImage root@<yourboard-ip>:/boot/