CL-SOM-iMX7: Linux: Kernel

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Overview

The Linux kernel for CL-SOM-iMX7 provides support for on-board peripherals/interfaces of CL-SOM-iMX7 system-on-module (SoM) and following derived devices built around the CL-SOM-iMX7 SoM:

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

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

Unzip the downloaded Linux package to a directory on your host workstation. The following discussion uses /path/to/cl-som-imx7-linux/ 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 or downloaded as a tarball from Freescale public git repository. The instructions below assume that the /home/development/cl-som-imx7/kernel directory has been created for CL-SOM-iMX7 kernel development.

Snapshot download

  • Extract the downloaded archive linux-2.6-imx-deb84cde0da96c5ccccb7e4c1204ad89ee801eca.tar.gz
cd /home/development/cl-som-imx7/kernel
tar xpf /path/to/downloaded/linux-2.6-imx-deb84cde0da96c5ccccb7e4c1204ad89ee801eca.tar.gz
mv linux-2.6-imx-deb84cde0da96c5ccccb7e4c1204ad89ee801eca linux-cl-som-imx7
  • Apply the CL-SOM-iMX7 patch
cd /home/development/cl-som-imx7/kernel/linux-cl-som-imx7
patch -p1 < /path/to/cl-som-imx7-linux/kernel/linux-4.1.15-cl-som-imx7-*.patch

Git clone

  • Install git version control system.
  • Create a clone of the FreeScale Linux kernel tree
cd /home/development/cl-som-imx7/kernel
git clone git://git.freescale.com/imx/linux-2.6-imx.git linux-cl-som-imx7
  • Create a branch for CL-SOM-iMX7 development. The CL-SOM-iMX7 patches are generated vs. deb84cde0da96c5ccccb7e4c1204ad89ee801eca commit 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 deb84cde0da96c5ccccb7e4c1204ad89ee801eca
  • Apply the CL-SOM-iMX7 patch
git am /path/to/cl-som-imx7-linux/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="imx7d-sbc-*imx7.dtb imx7d-cl-som-imx7.dtb"
make cl_som_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 the 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.
# 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 -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-iot-imx7.dtb - for IOT-GATE-iMX7 Internet of Things Gateway and SBC-IOT-iMX7 Internet of Things Single Board Computer

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.

Deploying the CL-SOM-iMX7 kernel and modules

  • 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=`cat /proc/cmdline | awk '{ for (i=1;i<=NF;i++) { if($i~/^root=/) { print substr($i,6,length($i)-6)"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 / -xvf /root/linux-image-cl-som-imx7.tar.gz

U-Boot Environment

MMC Boot Parameters

To boot from MMC/SD card type: 

setenv mmcdev 0
setenv mmcblk mmcblk0p2

Continue to the Common Boot Parameters.

eMMC Boot Parameters

To boot from internal eMMC storage type: 

setenv mmcdev 2
setenv mmcblk mmcblk2p2

Continue to the Common Boot Parameters.

Device Tree Blob

  • For SBC-iMX7 type:
setenv fdt_file imx7d-sbc-imx7.dtb
  • For IOT-GATE-iMX7 and SBC-IOT-iMX7 type:
setenv fdt_file imx7d-sbc-iot-imx7.dtb

Common Boot Parameters

To boot Linux type: 

setenv loadaddr 0x80800000
setenv fdt_addr 0x83000000
setenv image zImage
setenv bootargs console=ttymxc0,115200 root=/dev/${mmcblk} rw rootwait
mmc dev ${mmcdev}
load mmc ${mmcdev} ${loadaddr} ${image}
load mmc ${mmcdev} ${fdt_addr} ${fdt_file}
bootz ${loadaddr} - ${fdt_addr}

NFS Boot Parameters

To boot via network interface type: 

dhcp
setenv loadaddr 0x80800000
setenv fdt_addr 0x83000000
setenv image zImage
setenv nfsserver <nfs server ip address>
setenv tftpserver <tftp server ip address>
setenv bootargs console=ttymxc0,115200 root=/dev/nfs rw ip=dhcp nfsroot=${nfsserver}:${nfsroot}
tftpboot ${loadaddr} ${tftpserver}:${image}
tftpboot ${fdt_addr} ${tftpserver}:${fdt_file}
bootz ${loadaddr} - ${fdt_addr}

See also

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