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.