Enable SPI

If you want to use SPI bus, you have to enable it first:

Open /etc/modules on Rasbian:

sudo nano /etc/modules

or /etc/modules-load.d/raspberrypi.conf on Arch Linux:

sudo nano /etc/modules-load.d/raspberrypi.conf

and add these two lines to the end

spi-bcm2708
spidev

Check if file /etc/modprobe.d/raspi-blacklist.conf exist and open it:

sudo nano /etc/modprobe.d/raspi-blacklist.conf

Put # in front of spi line:

#blacklist spi-bcm2708
blacklist i2c-bcm2708

Reboot your system.