Building kernel modules

The Raspberry Pi is a very capable little machine, and there is support for common hardware devices provided out-of-the-box. However, you may come across a device that isn't supported, and need to build kernel modules to support it. This is remarkably simple once you get the right bits and pieces on your pi's filesystem, and quite a few people have produced how tos. Perhaps the most useful, and the one I've used to produce this guide is the one writte by Mchr3k on his blog in the article: 'Raspberry Pi Progress'. I've put my own steps below, but it is mainly based on his guide - thanks Mchr3k!

These instructions are tested on a clean install of debian straight from the Raspberry Pi website (I used version debian6-19-04-2012.zip), but you do need more than the default partition size, so resize the partition first (there's a useful guide here until I get around to writing one!).

We already have the build-essential package provided with the Pi which takes care of most of the compilation, but we need git to get the repository, libncurses5-dev to run the configuration menu and the command bc for the kernel build (not in build-essential).

sudo apt-get install git libncurses5-dev bc

Download the kernel sources from the Raspberry Pi source control repository, then link them to the kernel directory - I use a symlink here as means I can store the files on a larger filesystem (I have a USB attached drive)

git clone --depth 1 https://github.com/raspberrypi/linux.git
sudo ln -s `pwd`/linux /lib/modules/3.1.9+/build

Then, we get ready to do the kernel build. The Pi stores the current kernel configuration in the /proc/ filesystem, so we can use that to provide an initial setup - all these commands need to be done from the ~/linux directory.

gzip -dc /proc/config.gz > .config

Set up your new kernel, setting what you need to [M] in the configuration.

make menuconfig

Set up the building process, and start the build - NOTE you have to build the entire kernel the first time to ensure that the symbols are synchronised - the kernel doesn't need to be used for the modules to work (and if you want to add more modules in future, you can just do make modules) - does anyone know how to avoid having to do this?

make

Go and have a lot of coffee - this step takes a significant amount of time - like, about 6 hours!

Once this is done, and if you have any build errors, let me know, I may be able to point you in the right direction, we can now go ahead and install the modules:

sudo make modules_install

If the drivers you require also have firmware, then install that, too:

sudo make firmware_install

All done - congratulations!