How to Build the Modules for adding an mcp251x to a Raspberry Pi
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Note: The examples shown here were run with Kernel 3.10.24+ from Raspbian 2013-12-20.

Chapter 1: Find your kernel hash and configuration (on the Pi)
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- Find your kernel hash using either of the following methods:

> FIRMWARE_HASH=$(zgrep "* firmware as of" /usr/share/doc/raspberrypi-bootloader/changelog.Debian.gz | head -1 | awk '{ print $5 }')
> KERNEL_HASH=$(wget https://raw.github.com/raspberrypi/firmware/$FIRMWARE_HASH/extra/git_hash -O -)
> echo $KERNEL_HASH
4bbea92eae6c0792e85a4ba079d367ac6aa77fb5

or, if you got your kernel via rpi-update (scroll down): https://github.com/raspberrypi/linux/issues/486

- Get the configuration of your running kernel:

> cp /proc/config.gz ~


Chapter 2: Setup your build environment (on a different, *very* fast machine)
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See http://elinux.org/RPi_Kernel_Compilation for additional basic information.

- Setup a Linux System or VM
- make a folder for compilation:

> mkdir ~/raspi; export BASEDIR=~/raspi; cd $BASEDIR

- Get the kernel sources:

> cd $BASEDIR
> git clone --depth 100 https://github.com/raspberrypi/linux.git
> export KERNEL_SRC=$BASEDIR/linux
> cd $KERNEL_SRC
> git checkout 4bbea92eae6c0792e85a4ba079d367ac6aa77fb5

Note that the hash value for git checkout is the one you got in Chapter 1.

- Get the Compiler

> cd $BASEDIR
> git clone git://github.com/raspberrypi/tools.git
> export CCDIR=$BASEDIR/tools/arm-bcm2708/arm-bcm2708-linux-gnueabi/bin
> export CCPREFIX=$CCDIR/arm-bcm2708-linux-gnueabi-

Chapter 3: Compile the Kernel modules
-------------------------------------

- Prime the Kernel sources with the old configuration

> cd $BASEDIR
> scp pi@raspberry:config.gz .
> cd $KERNEL_SRC
> zcat $BASEDIR/config.gz > .config
> ARCH=arm CROSS_COMPILE=${CCPREFIX} make oldconfig

- Add the CAN modules and drivers to the configuration.

> ARCH=arm CROSS_COMPILE=${CCPREFIX} make menuconfig

For what options to select, see http://elinux.org/RPi_CANBus
Note that when an option is selected to be compiled into the kernel (shows a *), you do *not* need to change that to module!

- Compile the kernel

> ARCH=arm CROSS_COMPILE=${CCPREFIX} make

This will take a while. If you have multiple cores available in your VM, speed up compilation by using "-j <numcors+1>". So for my VM with 3 cores available, I use

> ARCH=arm CROSS_COMPILE=${CCPREFIX} make -j 4

- Create a directory to temporarily deploy the modules in

> mkdir $BASEDIR/modules
> export MODULES_TEMP=$BASEDIR/modules

- Deploy the modules:

> ARCH=arm CROSS_COMPILE=${CCPREFIX} INSTALL_MOD_PATH=${MODULES_TEMP} make modules_install

- Get the source for the spi-config module

> cd $BASEDIR
> git clone https://github.com/msperl/spi-config
> cd spi-config

- Build the spi-config module

> ARCH=arm CROSS_COMPILE=${CCPREFIX} make KDIR=$KERNEL_SRC

- Deploy the spi-config module

> ARCH=arm CROSS_COMPILE=${CCPREFIX} INSTALL_MOD_PATH=${MODULES_TEMP} make KDIR=$KERNEL_SRC install

- Pack all necessary modules into one tar file:

> cd $MODULES_TEMP
> tar -cjf rpi-can-modules.tar.bz2 \
lib/modules/3.10.24+/kernel/net/can/can.ko \
lib/modules/3.10.24+/kernel/net/can/can-raw.ko \
lib/modules/3.10.24+/kernel/net/can/can-gw.ko \
lib/modules/3.10.24+/kernel/net/can/can-bcm.ko \
lib/modules/3.10.24+/kernel/drivers/net/can/mcp251x.ko \
lib/modules/3.10.24+/kernel/drivers/net/can/can-dev.ko \
lib/modules/3.10.24+/kernel/drivers/spi/spi-bcm2708.ko \
lib/modules/3.10.24+/extra/spi-config.ko

- Copy the resulting archive to the Pi

> scp rpi-can-modules.tar.bz2 pi@raspberrypi:

Chapter 4: Deploy the modules on the Pi (on the Pi, obviously)
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- Exctract the modules

> cd /
> sudo tar -xjf ~/rpi-can-modules.tar.bz2
> sudo depmod -a

- Test-load the modules

> sudo modprobe spi-bcm2708
> sudo modprobe can
> sudo modprobe can-dev
> sudo modprobe can-raw
> sudo modprobe can-bcm
> sudo modprobe spi-config devices=\
bus=0:cs=0:modalias=mcp2515:speed=10000000:gpioirq=25:pd=20:pds32-0=16000000:pdu32-4=0x2002:force_release

If you see "mcp251x spi0.0: probed", it worked.