CL-SOM-iMX7: Linux: Kernel

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Overview

The Linux kernel for CL-SOM-iMX7 provides support for on-board peripherals and abstracts the functionality provided by the hardware.

Kernel boot process

Default boot process

The CL-SOM-iMX7 U-Boot scans the various boot devices and loads the kernel from the first valid boot device. The boot device is valid when:

  • physically present
  • boot partition formatted with vfat or ext2/3/4
  • has kernel image and a DTB file that meet the board configuration
  • or boot.scr in the root of the boot partition

Default boot device layout

The CL-SOM-iMX7 default boot device layout:

  • /boot/zImage-cl-som-imx7 - Linux kernel zImage
  • /boot/imx7d-sbc-imx7l.dtb - SBC-iMX7 board device tree blob (Evaluation Board)
  • /boot/imx7d-cl-som-imx7.dtb - CL-SOM-iMX7 module device tree blob

Building kernel for CL-SOM-iMX7

Cross-Compiler

There are several options for cross-compilation toolchain setup. You can either compile your cross-compiler or use an already built cross-compiler. The cross-compiler should support the ARM embedded-application binary interface ("EABI")

  • Pre-built toolchain:
  • Tools for creating cross-compilers:
    • Crosstool-ng: Builds a cross-compiler from source. Non-distribution specific.
    • Crossdev: Gentoo's cross-compiler builder. Needs Gentoo.

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

  • Download rel_imx_3.14.52_1.1.0_ga snapshot with your web browser.
  • Extract the downloaded archive rel_imx_3.14.52_1.1.0_ga.tar.gz
cd /home/development/cl-som-imx7/kernel
tar xpf /path/to/downloaded/rel_imx_3.14.52_1.1.0_ga.tar.gz
mv rel_imx_3.14.52_1.1.0_ga linux-cl-som-imx7

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. rel_imx_3.14.52_1.1.0_ga tag (5f6f0a50e6039370078369ddf380179d59024789 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 rel_imx_3.14.52_1.1.0_ga

Apply the CL-SOM-iMX7 patch

cd /home/development/cl-som-imx7/kernel/linux-cl-som-imx7
git am /path/to/cl-som-imx7-linux/kernel/patches/*.patch

Building the kernel

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/arch/arm/boot
  • device tree blobs will be created in /home/development/CL-SOM-iMX7/kernel/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/arch/arm/boot directory.
# ls -al /home/development/CL-SOM-iMX7/kernel/arch/arm/boot/zImage
  • DTB files
# cd /home/development/CL-SOM-iMX7/kernel/arch/arm/boot/dtb/
# 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/include/config/kernel.release
# cat /home/development/CL-SOM-iMX7/kernel/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/arch/arm/boot/zImage /home/development/CL-SOM-iMX7/rootfs/boot/zImage-cl-som-imx7
# cd /home/development/CL-SOM-iMX7/kernel/arch/arm/boot/dtb/
# 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-sbc-imx7.dtb imx7d-cl-som-imx7.dtb files of the Linux kernel source tree.

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-cl-som-imx7 /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.

Common Boot Parameters

To boot Linux type: 

setenv loadaddr 0x80800000
setenv fdt_addr 0x83000000
setenv image zImage-cl-som-imx7
setenv fdt_file imx7d-sbc-imx7.dtb
setenv bootargs console=ttymxc0,115200 root=/dev/${mmcblk} rw rootwait ip=dhcp
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: 

setenv loadaddr 0x80800000
setenv fdt_addr 0x83000000
setenv image zImage-cl-som-imx7
setenv fdt_file imx7d-sbc-imx7.dtb
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}

dhcp
tftpboot ${loadaddr} ${tftpserver}:${image}
tftpboot ${fdt_addr} ${tftpserver}:${fdt_file}
bootz ${loadaddr} - ${fdt_addr}

See also

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