rasp-config

User friendly interface for hardware configuration

yaourt -s rasp-config

SPI

To enable the /dev/spidev* devices:

/boot/config.txt

dtparam=spi=on

I2C

Install i2c-tools

/boot/config.txt

dtparam=i2c=on dtparam=i2c_baudrate=400000

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

i2c-dev i2c-bcm2708

Reboot and run i2cdetect -y 1 (/dev/i2c-1)

For more information

/boot/config.txt manual