SOCs have a standard set of tuples consisting of frequency and
voltage pairs that the device will support per voltage domain. This
is called Operating Performance Point or OPP. The actual definitions
of OPP varies over silicon within the same family of devices.

OPP layer organizes the data internally using device pointers
representing individual voltage domains and provides SOC
implementations a ready to use framework to manage OPPs.
For more information, read Documentation/power/opp.txt