Linux Kernel

'''This page provides information about the legacy linux-sunxi kernels, which are based on the vendor code drops. It is only useful when accelerated 3D graphics and multimedia support is strictly necessary.'''

'''But the Mainline Kernel is already a much better choice for a headless server. And also the mainline kernel works fine even for a basic Linux desktop system running on top of a simple framebuffer, which may be good enough for the users who do not need fancy 3D graphics or video playback acceleration.'''

This page describes how to get the sunxi specific linux kernel built for your device.

= History =

Public Linux Kernel support for the sunxi family (Allwinner A10, A13, ...) started with a source drop of 2.6.36 made by Ainol, followed by an official release of 2.6.36 sources by Allwinner. Developement jumped forward after a source release of 3.0.8 made by Qware

Initially living in amery's github now our community driven sunxi kernel repo is located in the linux-sunxi's github.

= Repository =

The main sunxi kernel repository is available at our projects github.

You can clone the entire (huge) repository by installing the git package and running:

git clone https://github.com/linux-sunxi/linux-sunxi.git

but if you just want to build our kernel, then follow the guide below.

= Kernel versions =

Parts of the sunxi SoC are already supported by mainline kernel 3.8 and onwards.

In case you need 3D and audio support (for A10/A20), you should can check out the sunxi-3.4 branch as this will get the most out of your hardware quickly. But beware that this is already obsolete and unmaintained.

If unsure, use the sunxi-3.4 branch.

= Compilation =

Get a toolchain
If you haven't done so before, get a suitable toolchain installed and added to your PATH.

Clone the repository
This command will clone the sunxi-3.4 branch:

git clone -b sunxi-3.4 https://github.com/linux-sunxi/linux-sunxi.git

If you just want a quick build and do not wish to download a big git repository, then run:

git clone -b sunxi-3.4 --depth 1 https://github.com/linux-sunxi/linux-sunxi.git

This will create a so-called shallow clone (still a 500MB download), which does not allow for much in the way of development or changes.

A10
For A10 use:

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- sun4i_defconfig

A13
For A13 use: make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- sun5i_defconfig

A10s
For A10s use: make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- sun5i_defconfig

But to get a booting system, you need to set: CONFIG_SW_DEBUG_UART=1 to: CONFIG_SW_DEBUG_UART=0

in .config.

Through menuconfig, you need to dig through: System Type ---> Then: Allwinner's sunxi options ---> And then set this to 0: (1) UART to use for low-level debug

A20
For A20 use: make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- sun7i_defconfig

Tweak config
After you have set a default configuration, you can fine-tune your kernel configuration.

For this you will need ncurses development code installed. So for example, on a system that uses the apt package manager, run the following:

apt-get install libncurses5-dev

Now you can run menuconfig, and edit your configuration:

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig

Note that the sunxi kernel is based on an obsolete kernel version with vendor hacks thrown in to support the sunxi hardware. As a result some configurations that are possible to select will not build or work.

In particular some sunxi-specific drivers were not fixed to work both as built-in and as module and IPv6 only works as built-in.

If you plan on using a rootfs with systemd or upstart (e.g. Ubuntu) you should set CONFIG_FHANDLE=y in the kernel configuration. By default, .config reads "# CONFIG_FHANDLE is not set" The option can be found in General Setup, Open by fhandle syscalls.

Build
Make sure you have the package u-boot-tools installed, then:

make -j4 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- uImage modules

The -j4 option runs 4 make instances in parallel to speed up compilation. Please adjust this to the number of CPU cores/thread execution units available.

As a final step, create the full module tree: make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- INSTALL_MOD_PATH=output modules_install

The INSTALL_MOD_PATH option specifies the directory where the full module tree will be made available, in this example, it will be the output directory under the kernel build directory itself.

Install
Now you have the following sitting in your kernel tree:

arch/arm/boot/uImage output/lib/modules/3.4.XXX/

The uImage file (the kernel minus the modules) needs to be started by u-boot, so it is usually copied to a boot partition where u-boot will find it, load it in RAM and then transfer control to it (u-boot can also pass parameters to the kernel). The modules directory needs to be copied to the /lib/modules on the target root file system.

= Upstream code =

There is some sunxi code available in Linus' tree. But this is not suited for normal use yet, and will likely need a lot more work to get there. For more information, see our mainline kernel howto.

= External links =
 * Official linux-sunxi git repository

= References =