CL-SOM-iMX7: Linux: Kernel

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The CL-SOM-iMX7 Linux kernel provides support for on-board peripherals/interfaces of the CL-SOM-iMX7 System-on-Module and the following CompuLab products built around CL-SOM-iMX7:

  • SBC-iMX7 Single Board Computer
  • SBC-IOT-iMX7 Internet of Things Single Board Computer
  • IOT-GATE-iMX7 Internet of Things Gateway

BSP packages for different CompuLab i.MX7 devices may differ from each other. It is recommended to use the most recent BSP package released for the specific device being used. It can be downloaded from the corresponding product web page:

Unzip the downloaded BSP source package to a directory on your host workstation. The following instructions use /path/to/cl-som-imx7-bsp-src/ template for this location. Please use the real path to the Linux package instead.

Building kernel for CL-SOM-iMX7

Getting kernel sources

Linux git tree can be cloned from the Code Aurora. The instructions below assume that the /home/development/cl-som-imx7/kernel directory has been created for CL-SOM-iMX7 kernel development.

Git clone

  • Install git version control system.
  • Create a clone of the NXP Linux kernel tree
cd /home/development/cl-som-imx7/kernel
git clone linux-cl-som-imx7
  • Create a branch for CL-SOM-iMX7 development. The CL-SOM-iMX7 patches are generated vs. rel_virt_4.14.98_4.11_0.10_ga tag in the Linux tree. It is recommended to use exactly the same baseline to avoid merge conflicts.
cd /home/development/cl-som-imx7/kernel/linux-cl-som-imx7
git checkout -b development rel_virt_4.14.98_4.11_0.10_ga
  • Apply the CL-SOM-iMX7 patch
git am /path/to/cl-som-imx7-bsp-src/kernel/patches/*.patch

Building the kernel

cd /home/development/cl-som-imx7/kernel/linux-cl-som-imx7
export ARCH=arm
export CROSS_COMPILE=arm-none-linux-eabi-
export DTB=$(ls -al arch/arm/boot/dts | awk '(/imx7d-.*imx7.*\.dts$/)&&($0=$NF)$$(gsub(/dts/,"dtb"))')
make compulab_imx7_defconfig
make menuconfig
make zImage modules ${DTB} && INSTALL_MOD_PATH=/home/development/cl-som-imx7/rootfs make modules_install

In the example above:

  • Linux kernel image (zImage) will be created in /home/development/cl-som-imx7/kernel/linux-cl-som-imx7/arch/arm/boot
  • device tree blobs will be created in /home/development/cl-som-imx7/kernel/linux-cl-som-imx7/arch/arm/boot/dts
  • loadable kernel modules will be installed into the /home/development/cl-som-imx7/rootfs/lib/modules directory.

When CL-SOM-iMX7 is booted with the kernel image created as described above and with networked root filesystem at /home/development/cl-som-imx7/rootfs/, the system will be able to load the kernel modules properly, thus avoiding module version problems.

zImage, DTB files and modules locations

  • In the example above, the Linux kernel image (zImage) will be created in the /home/development/cl-som-imx7/kernel/linux-cl-som-imx7/arch/arm/boot directory.
# ls -al /home/development/cl-som-imx7/kernel/linux-cl-som-imx7/arch/arm/boot/zImage
  • DTB files
# cd /home/development/cl-som-imx7/kernel/linux-cl-som-imx7/arch/arm/boot/dts/
# ls -al ${DTB}
# cd -
  • The loadable kernel modules will be installed into the /home/development/cl-som-imx7/rootfs/lib/modules directory.
# ls -al /home/development/cl-som-imx7/rootfs/lib/modules

Kernel Version

  • In the example above, the Linux kernel release version number will be saved in /home/development/cl-som-imx7/kernel/linux-cl-som-imx7/include/config/kernel.release
# cat /home/development/cl-som-imx7/kernel/linux-cl-som-imx7/include/config/kernel.release

Prepare kernel and modules tarball

  • In the example below, the Linux kernel and modules are packed into the tar archive for deploying onto the CL-SOM-iMX7 on-board eMMC storage.
# mkdir -p /home/development/cl-som-imx7/rootfs/boot
# cp -v /home/development/cl-som-imx7/kernel/linux-cl-som-imx7/arch/arm/boot/zImage /home/development/cl-som-imx7/rootfs/boot/
# cd /home/development/cl-som-imx7/kernel/linux-cl-som-imx7/arch/arm/boot/dts/
# cp -v ${DTB} /home/development/cl-som-imx7/rootfs/boot/ 
# cd -
# tar --keep-directory-symlink -C /home/development/cl-som-imx7/rootfs -czvf /home/development/cl-som-imx7/linux-image-cl-som-imx7.tar.gz .

Basic platform support

The CL-SOM-iMX7 basic platform support is implemented in the imx7d-cl-som-imx7.dtb file of the Linux kernel source tree. The extended interface support depends on carrier board used and thus is implemented in the Single Board Computer device tree files:

  • imx7d-sbc-imx7.dtb - for SBC-iMX7 Single Board Computer
    • imx7d-sbc-imx7-m4.dtb - for SBC-iMX7 Single Board Computer with Cortex-M4 core support
    • imx7d-sbc-imx7-lvds.dtb - device tree blob for SBC-iMX7 Single Board Computer with LVDS support
  • imx7d-sbc-iot-imx7.dtb - for IOT-GATE-iMX7 IoT Gateway and SBC-IOT-iMX7 Single Board Computer
    • imx7d-sbc-iot-imx7-can.dtb - for IOT-GATE-iMX7 and SBC-IOT-iMX7 with CAN bus support
    • imx7d-sbc-iot-imx7-rs485-hdx.dtb - for IOT-GATE-iMX7 and SBC-IOT-iMX7 with RS485 half duplex support

These files contain:

  • default setup of multi-functional pins;
  • registration of the devices integrated in the CL-SOM-iMX7 module;
  • definitions of platform-specific configuration for these devices.

Alternative DTS file with additional peripherals: imx7d-sbc-imx7.dtb.

Deploying the CL-SOM-iMX7 kernel and modules onto eMMC

  • Boot up the CL-SOM-iMX7 computer.
  • Copy the previously created linux-image-cl-som-imx7.tar.gz to /root directory of the CL-SOM-iMX7.

Mount boot partition

  • Use the below command to mount the boot partition for installing the CL-SOM-iMX7 Linux kernel binary:
# boot_partition=$(boot_partition=$(findmnt -o SOURCE -n /); cat <<< ${boot_partition:0:-1}1)
# mount $boot_partition /boot

Back up old kernel

  • It is essential to backup the old (known to work) kernel binary.
# mkdir /boot/`uname -r`
# mv /boot/zImage* /boot/*.dtb /boot/`uname -r`/

Installing kernel and modules

Assuming that the linux-image-cl-som-imx7.tar.gz tar ball has been copied to the CL-SOM-iMX7 /root directory.

  • Extract and install the Linux kernel binary:
# tar -C / --keep-directory-symlink -xvf /root/linux-image-cl-som-imx7.tar.gz

Device Tree Examples

The provided device tree in the BSP package is no using all the interfaces in the evaluation board.

See also