en:c2_building_kernel [ODROID Wiki]

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====== Kernel ======
This page introduce how you can download and compile the Linux kernel for **ODROID-C2**.
===== Cross Compile - HOST-PC/Ubuntu =====
==== Installing required packages ====
You will need install required packages before you start to build Linux kernel on your Ubuntu desktop.
<code>
$ sudo apt-get update
$ sudo apt-get install git lzop build-essential gcc libncurses5-dev libc6-i386
</code>

==== Toolchain (4.9.2) ====
Click one of the site to download toolchain to build Linux kernel.
  * [[http://releases.linaro.org/14.09/components/toolchain/binaries/gcc-linaro-aarch64-linux-gnu-4.9-2014.09_linux.tar.xz|Download #1]]
Once the download is done, extract the tarball to **/opt/toolchains/**.
<code>
$ sudo mkdir -p /opt/toolchains
$ sudo tar Jxvf gcc-linaro-aarch64-linux-gnu-4.9-2014.09_linux.tar.xz -C /opt/toolchains/
</code>
In order to add the toolchain path to PATH, paste below lines to **$HOME/.bashrc**.
<code>
export ARCH=arm64
export CROSS_COMPILE=aarch64-linux-gnu-
export PATH=/opt/toolchains/gcc-linaro-aarch64-linux-gnu-4.9-2014.09_linux/bin/:$PATH
</code>
You can apply the change if you login again or import 
to apply this change, login again or evaluate **$HOME/.bashrc** with source command.
<code>
$ source ~/.bashrc
</code>
You can check if the toolchain installed above works properly while checking the version of toolchain. If you can find **gcc version 4.9.2 20140904 (prerelease)** at the end of the line, the toolchain is well installed.
<code>
$ aarch64-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=aarch64-linux-gnu-gcc
COLLECT_LTO_WRAPPER=/opt/toolchains/aarch64-linux-4.9/bin/../libexec/gcc/aarch64-linux-gnu/4.9.2/lto-wrapper
Target: aarch64-linux-gnu
Configured with: /cbuild/slaves/oorts/crosstool-ng/builds/aarch64-linux-gnu-linux/.build/src/gcc-linaro-4.9-2014.09/configure --build=i686-build_pc-linux-gnu --host=i686-build_pc-linux-gnu --target=aarch64-linux-gnu --prefix=/cbuild/slaves/oorts/crosstool-ng/builds/aarch64-linux-gnu-linux/install --with-sysroot=/cbuild/slaves/oorts/crosstool-ng/builds/aarch64-linux-gnu-linux/install/aarch64-linux-gnu/libc --enable-languages=c,c++,fortran --disable-multilib --enable-multiarch --with-arch=armv8-a --with-pkgversion='crosstool-NG linaro-1.13.1-4.9-2014.09 - Linaro GCC 4.9-2014.09' --with-bugurl=https://bugs.launchpad.net/gcc-linaro --enable-__cxa_atexit --disable-libmudflap --enable-libgomp --disable-libssp --with-gmp=/cbuild/slaves/oorts/crosstool-ng/builds/aarch64-linux-gnu-linux/.build/aarch64-linux-gnu/build/static --with-mpfr=/cbuild/slaves/oorts/crosstool-ng/builds/aarch64-linux-gnu-linux/.build/aarch64-linux-gnu/build/static --with-mpc=/cbuild/slaves/oorts/crosstool-ng/builds/aarch64-linux-gnu-linux/.build/aarch64-linux-gnu/build/static --with-isl=/cbuild/slaves/oorts/crosstool-ng/builds/aarch64-linux-gnu-linux/.build/aarch64-linux-gnu/build/static --with-cloog=/cbuild/slaves/oorts/crosstool-ng/builds/aarch64-linux-gnu-linux/.build/aarch64-linux-gnu/build/static --with-libelf=/cbuild/slaves/oorts/crosstool-ng/builds/aarch64-linux-gnu-linux/.build/aarch64-linux-gnu/build/static --enable-threads=posix --disable-libstdcxx-pch --enable-linker-build-id --enable-plugin --with-local-prefix=/cbuild/slaves/oorts/crosstool-ng/builds/aarch64-linux-gnu-linux/install/aarch64-linux-gnu/libc --enable-c99 --enable-long-long
Thread model: posix
gcc version 4.9.2 20140904 (prerelease) (crosstool-NG linaro-1.13.1-4.9-2014.09 - Linaro GCC 4.9-2014.09) 
</code>

==== Checkout ====
You can checkout Linux kernel source tree from **[[https://github.com/hardkernel/linux/tree/odroidc2-3.14.y-android|Hardkernel's Github]]**, please note that we distribute the Linux kernel in different branches for Android and other Linux distributions.

=== Android ===
<code>
$ git clone --depth 1 https://github.com/hardkernel/linux.git -b odroidc2-3.14.y-android
$ cd linux
</code>

=== Linux ===
<code>
$ git clone --depth 1 https://github.com/hardkernel/linux.git -b odroidc2-3.14.y
$ cd linux
</code>
==== Compile ====

<WRAP center round important 100%>
**Note**
  * If you want to download & build only **Android Linux kernel** source code without another Android BSP, you face the error message as below:
    *  //drivers/amlogic/wifi/Kconfig:26: can't open file "../hardware/wifi/realtek/drivers/8192cu/rtl8xxx_CU/Kconfig"//
  * Please delete the last line as below in **'drivers/amlogic/wifi/Kconfig'** file if you will build only Android Linux kernel.
    * <del>source "../hardware/wifi/realtek/drivers/8192cu/rtl8xxx_CU/Kconfig"</del>

</WRAP>

You must do kernel configuration for **ODROID-C2**, then start to build. Adding **-j** option on make command will help you to finish compiling faster.
<code>
$ make odroidc2_defconfig
$ make <-j4> Image dtbs modules
</code>
You have done to compile the Linux kernel (Image), the device tree file (.dtb) and kernel modules (.ko).

==== Custom Kernel Build ====
If you have some kernel drivers wish to include for your custom build, you can select the drivers easily in Linux kernel tree. **make menuconfig** will show you text based menus help you to select kernel drivers.
<code>
$ make menuconfig
</code>
Once you done selecting the drivers, exit from the menu screen. Then you can start kernel build with **make** again.
<code>
$ make <-j4> Image modules
</code>
When you exit from kernel menu screen, you will have **.config** in the current directory what have changes for your custom build. You can back up this as a file, my_kernel.config for example, or can make a patch if you manage your own git.
<code>
$ cp .config arch/arm64/configs/odroidc2_defconfig
$ git add arch/arm64/configs/odroidc2_defconfig
$ git commit -s -m "Change the kernel config file for ODROID-C2"
$ git push
</code>

==== Installation ====
There are different instructions to install Linux kernel image and device tree for Android and Linux. Since Android loads both from a boot partition, we have to use **fastboot** to install into the dedicated partition. Please refer the partition table from [[http://odroid.com/dokuwiki/doku.php?id=en:c2_partition_table|here]]. In contrast, Linux boots by the instructions described in **boot.ini** the 1st FAT partition.

=== Android ===
This is the instruction to install kernel image, **Image**, to the boot card.
<code>
$ fastboot flash boot <path/of/your/Image>
</code>
This is to install a device tree file, **meson64_odroidc2.dtb**.
<code>
$ fastboot flash dtb <path/of/your/meson64_odroidc2.dtb>
</code>

=== Linux ===
<WRAP center round important 100%>
** This explanation assume that your USB memory CARD reader is assigned at /dev/sdc. Be careful!**
</WRAP>

1. Plug the Boot-Device(eMMC or SD) into the USB memory CARD reader and Connect the USB memory CARD reader to your HOST PC(Linux OS).

2. Copy the Image and DT(meson64_odroidc2.dtb) to the FAT partition(1st partition) in the Boot-Device.
<code>
$ mkdir -p mount
$ sudo mount /dev/sdc1 ./mount
$ sudo cp arch/arm64/boot/Image arch/arm64/boot/dts/meson64_odroidc2.dtb ./mount && sync && sudo umount ./mount
</code>

3. Copy the driver modules to the EXT4 partition(2nd partition) in the Boot-Device.
<code>
$ sudo mount /dev/sdc2 ./mount
$ sudo make modules_install ARCH=arm64 INSTALL_MOD_PATH=./mount && sync && sudo umount ./mount
$ rm -rf mount
</code> 

===== Native Compile - ODROID-C2/Ubuntu =====
<WRAP center round important 100%>
**Note**
  * 8GB eMMC/SD card have not enough space to build kernel source. In order to do native compile, the  **5GB** of storage space is required at least.
</WRAP>
==== Installing required packages ====
You will need install required packages before you start to build Linux kernel on your Ubuntu ODROID-C2.
<code>
odroid@odroid64:~$ sudo apt-get update
odroid@odroid64:~$ sudo apt-get install git
</code>

==== Toolchain (4.9.2) ====
The kernel for ODROID-C2 does not support gcc 5.x version yet. So, you must change to the gcc 4.9 version in order to build ODROID-C2 kernel.
<code>
odroid@odroid64:~$ sudo apt-get install gcc-4.9
odroid@odroid64:~$ sudo rm /usr/bin/gcc
odroid@odroid64:~$ sudo ln -s /usr/bin/gcc-4.9 /usr/bin/gcc
odroid@odroid64:~$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/aarch64-linux-gnu/4.9/lto-wrapper
Target: aarch64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.9.3-12ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-4.9/u
Thread model: posix
gcc version 4.9.3 (Ubuntu/Linaro 4.9.3-12ubuntu1) 
</code>

==== Checkout ====
<code>
odroid@odroid64:~$ git clone --depth 1 https://github.com/hardkernel/linux.git -b odroidc2-3.14.y
odroid@odroid64:~$ cd linux
</code>

==== Compile & Installation ====
<code>
odroid@odroid64:~/linux$ make odroidc2_defconfig
odroid@odroid64:~/linux$ make -j4
odroid@odroid64:~/linux$ sudo make modules_install
odroid@odroid64:~/linux$ sudo cp -f arch/arm64/boot/Image arch/arm64/boot/dts/meson64_odroidc2.dtb /media/boot/
odroid@odroid64:~/linux$ sudo sync
odroid@odroid64:~/linux$ sudo reboot
</code>