A DIF is a “Device Interface Function”. DIFs are low-level routines for accessing the hardware functionality directly, and are agnostic to the particular environment or context they are called from. The intention is that DIFs can be used during design verification, and during early silicon verification, and by the high-level driver software in production firmware.
This subtree provides headers and libraries known collectively as the DIF libraries.
There is one DIF library per hardware IP, and each one contains the DIFs required to actuate all of the specification-required functionality of the hardware they are written for.