Grinberg: /* Getting kernel sources */

2016-01-07T11:04:46Z

‎Getting kernel sources

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== Overview ==
The Linux kernel for CL-SOM-iMX6UL provides support for on-board peripherals and abstracts the functionality provided by the hardware.

== Kernel boot process ==
=== Default boot process ===
The CL-SOM-iMX6UL 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
* has {{filename|zImage-cl-som-imx6ul}} and a DTB file that meets the board configuration
* or {{filename|boot.scr}} in the root of the boot partition

=== Default boot device layout ===
The CL-SOM-iMX6UL default boot device layout:
* {{filename|/boot/zImage-cl-som-imx6ul}} - Linux kernel zImage
* {{filename|/boot/imx6ul-sbc-imx6ul.dtb}} - SBC-iMX6UL board device tree blob with P9 mmc slot enabled (Evaluation Board)
* {{filename|/boot/imx6ul-sbc-imx6ul-wilink.dtb}} - SBC-iMX6UL board device tree blob with WiLinki8 WiFi enabled (Evaluation Board)
* {{filename|/boot/imx6ul-cl-som-imx6ul.dtb}} - CL-SOM-iMX6UL module device tree blob with mmc 0 device enabled
* {{filename|/boot/imx6ul-cl-som-imx6ul-wilink.dtb}} - CL-SOM-iMX6UL module device tree blob with WiLink8 WiFi enabled

== Building kernel for CL-SOM-iMX6UL ==
=== 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 ("[http://en.wikipedia.org/wiki/Application_binary_interface#EABI EABI]")
* Pre-built toolchain:
** [http://www.codesourcery.com/sgpp/lite/arm/portal/release324 CodeSourcery]
* Tools for creating cross-compilers:
** [http://ymorin.is-a-geek.org/dokuwiki/projects/crosstool Crosstool-ng]: Builds a cross-compiler from source. Non-distribution specific.
** [http://www.gentoo.org/proj/en/base/embedded/handbook/index.xml?part=1&chap=4 Crossdev]: Gentoo's cross-compiler builder. Needs Gentoo.

=== Getting kernel sources ===
Linux git tree can be cloned or downloaded as a tarball from [http://git.freescale.com/git/cgit.cgi/imx/linux-2.6-imx.git/ Freescale public git repository].
The instructions below assume that the {{filename|/home/development/CL-SOM-iMX6UL/kernel}} directory has been created for CL-SOM-iMX6UL kernel development.

==== Git clone ====
* Install [http://git-scm.com/ git] version control system.
* Create a clone of the FreeScale Linux kernel tree
<pre>
cd /home/development/CL-SOM-iMX6UL/kernel
git clone git://git.freescale.com/imx/linux-2.6-imx.git .
git checkout -b development rel_imx_3.14.38_6ul_ga
</pre>

==== Apply the CL-SOM-iMX6UL patch ====
<pre>
git am /path/to/cl-som-imx6ul-linux/kernel/patches/*.patch
</pre>

=== Building the kernel ===
<pre>
export ARCH=arm
export CROSS_COMPILE=arm-none-linux-eabi-
export DTB="imx6ul-sbc-imx6ul.dtb imx6ul-sbc-imx6ul-wilink.dtb imx6ul-cl-som-imx6ul.dtb imx6ul-cl-som-imx6ul-wilink.dtb"
make cl_som_imx6ul_defconfig
make menuconfig
make zImage modules ${DTB} && INSTALL_MOD_PATH=/home/development/CL-SOM-iMX6UL/rootfs make modules_install
</pre>

In the example above:
* Linux kernel image ({{filename|zImage}}) will be created in {{filename|/home/development/CL-SOM-iMX6UL/kernel/arch/arm/boot}}
* device tree blobs will be created in {{filename|/home/development/CL-SOM-iMX6UL/kernel/arch/arm/boot/dts}}
* loadable kernel modules will be installed into the {{filename|/home/development/CL-SOM-iMX6UL/rootfs/lib/modules}} directory.
<br>
When the CL-SOM-iMX6UL is booted with the kernel image created as described above and with networked root filesystem at {{filename|/home/development/CL-SOM-iMX6UL/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 ({{filename|zImage}}) will be created in the {{filename|/home/development/CL-SOM-iMX6UL/kernel/arch/arm/boot}} directory.
<pre>
# ls -al /home/development/CL-SOM-iMX6UL/kernel/arch/arm/boot/zImage
</pre>
* DTB files
<pre>
# cd /home/development/CL-SOM-iMX6UL/kernel/arch/arm/boot/dtb/
# ls -al ${DTB}
# cd -
</pre>
* The loadable kernel modules will be installed into the {{filename|/home/development/CL-SOM-iMX6UL/rootfs/lib/modules}} directory.
<pre>
# ls -al /home/development/CL-SOM-iMX6UL/rootfs/lib/modules
</pre>

==== Kernel Version ====

* In the example above, the Linux kernel release version number will be saved in {{filename|/home/development/CL-SOM-iMX6UL/kernel/include/config/kernel.release}}
<pre>
# cat /home/development/CL-SOM-iMX6UL/kernel/include/config/kernel.release
</pre>

==== 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-iMX6UL.
<pre>
# mkdir -p /home/development/CL-SOM-iMX6UL/rootfs/boot
# cp -v /home/development/CL-SOM-iMX6UL/kernel/arch/arm/boot/zImage /home/development/CL-SOM-iMX6UL/rootfs/boot/zImage-cl-som-imx6ul
# cd /home/development/CL-SOM-iMX6UL/kernel/arch/arm/boot/dtb/
# cp -v ${DTB} /home/development/CL-SOM-iMX6UL/rootfs/boot/
# cd -
# tar -C /home/development/CL-SOM-iMX6UL/rootfs -czvf /home/development/CL-SOM-iMX6UL/linux-image-CL-SOM-iMX6UL.tar.gz .
</pre>

== Basic platform support ==

The CL-SOM-iMX6UL basic platform support is implemented in the {{parameter|imx6ul-sbc-imx6ul.dtb imx6ul-sbc-imx6ul-wilink.dtb imx6ul-cl-som-imx6ul.dtb imx6ul-cl-som-imx6ul-wilink.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-iMX6UL module;
* definitions of platform-specific configuration for these devices.

=== SBC-iMX6UL ===
* MMC: arch/arm/boot/dts/imx6ul-sbc-imx6ul.dts

<pre>
/*
* Suppport for CompuLab SB-SOM-iMX6UL baseboard
*/

#include "imx6ul-cl-som-imx6ul.dts"
#include "imx6ul-sb-som-imx6ul.dtsi"

/ {
model = "Compulab iMX6UL on SB-SOM";
compatible = "fsl,imx6ul", "compulab,cl-som-imx6ul", "compulab,sbc-imx6ul";
};
</pre>
* WiFi: arm/boot/dts/imx6ul-sbc-imx6ul-wilink.dts
<pre>
/*
* Suppport for CompuLab SB-SOM-iMX6UL baseboard
*/

#include "imx6ul-cl-som-imx6ul-wilink.dts"
#include "imx6ul-sb-som-imx6ul.dtsi"

/ {
model = "Compulab iMX6UL on SB-SOM";
compatible = "fsl,imx6ul", "compulab,cl-som-imx6ul", "compulab,sbc-imx6ul";
};
</pre>

== Deploying the CL-SOM-iMX6UL kernel and modules ==

Boot up the CL-SOM-iMX6UL computer. Copy the previously created {{filename|linux-image-CL-SOM-iMX6UL.tar.gz}} to {{filename|/root}} directory of the CL-SOM-iMX6UL.

==== Mount boot partition ====
* Use the below command to mount the boot partition for installing the CL-SOM-iMX6UL Linux kernel binary:
<pre>
# 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
</pre>

==== Back up old kernel ====
* It is essential to backup the old (known to work) kernel binary.
<pre>
# mkdir /boot/`uname -r`
# mv /boot/uImage-cl-som-imx6ul /boot/zImage-cl-som-imx6ul /boot/*.dtb /boot/`uname -r`/
</pre>

==== Installing kernel and modules ====
Assuming that the {{filename|linux-image-CL-SOM-iMX6UL.tar.gz}} tar ball has been copied to the CL-SOM-iMX6UL {{filename|/root}} directory.
* Extract and install the Linux kernel binary:
<pre>
# tar -C / -xvf /root/linux-image-CL-SOM-iMX6UL.tar.gz
</pre>

== U-Boot Environment ==

=== Common parameters ===
<pre>
setenv loadaddr 0x82000000
setenv fdt_addr 0x83000000
setenv zimage zImage-cl-som-imx6ul
</pre>

=== MMC Boot Parameters ===
<pre>
setenv fdt_file imx6ul-sbc-imx6ul.dtb
setenv mmcdev 0
setenv bootargs console=ttymxc2,115200 root=/dev/mmcblk0p2 rw rootwait ip=dhcp

mmc dev ${mmcdev}
load mmc ${mmcdev} ${loadaddr} ${zimage}
load mmc ${mmcdev} ${fdt_addr} ${fdt_file}
bootz ${loadaddr} - ${fdt_addr}
</pre>

=== eMMC Boot Parameters ===
<pre>
setenv fdt_file imx6ul-sbc-imx6ul-wilink.dtb
setenv mmcdev 1
setenv bootargs console=ttymxc2,115200 root=/dev/mmcblk1p2 rw rootwait ip=dhcp

mmc dev ${mmcdev}
load mmc ${mmcdev} ${loadaddr} ${zimage}
load mmc ${mmcdev} ${fdt_addr} ${fdt_file}
bootz ${loadaddr} - ${fdt_addr}
</pre>

=== NFS Boot Parameters ===
<pre>
setenv fdt_file imx6ul-sbc-imx6ul-wilink.dtb
setenv nfsserver <nfs server ip address>
setenv tftpserver <tftp server ip address>
setenv bootargs console=ttymxc2,115200 root=/dev/nfs rw ip=dhcp nfsroot=${nfsserver}:${nfsroot}

dhcp
tftpboot ${loadaddr} ${tftpserver}:${zimage}
tftpboot ${fdt_addr} ${tftpserver}:${fdt_file}
bootz ${loadaddr} - ${fdt_addr}
</pre>

== See also ==

* [[CL-SOM-iMX6UL: Linux: Getting started]]
* [[CL-SOM-iMX6UL: Linux: Debian]]
* [[Linux: Development for ARM modules]]
* [[Linux: Debian: Minimal ARM filesystem]]
* [http://www.debian.org/doc/manuals/reference/index.en.html Debian Reference].
* [http://www.alsa-project.org ALSA project official website]

[[Category:Linux|Debian]]
[[Category:CL-SOM-iMX6UL|Linux: Debian]]

CL-SOM-iMX6UL: Linux: Kernel - Revision history

Grinberg: /* Getting kernel sources */