The PiFi DAC+ is a cheap Chinese clone of the HiFi Berry made by ukonline2000. It's based on the I2S digital audio converter (DAC) chip PCM5122.
The drivers are already included in the kernel, to activate them check:

• for the 3.12 kernel https://www.hifiberry.com/build/documentation/hifiberry-software-configuration/
• for the 4.x kernel https://www.hifiberry.com/build/documentation/configuring-linux-3-18-x/.