The functionality that the PS4 controller will offer when connected to a Windows PC is just basic functionality. What this means is the analog sticks and buttons will work just fine. As suspected the touchpad on the PlayStation 4 DualShock 4 controller will not be functional without extra driver support and Sony apparently has no desire to produce a driver for Windows use at this time.
We suspect from the reports that we have received that the PS4 controller will be recognized by Windows as a standard USB HID device when connected. Unlike the Xbox 360 controller, the PS4 controller can’t take advantage of the built-in Xinput functionality in Windows that allows the Xbox 360 controller to be recognized as an actual Xbox 360 controller in Windows.
A driver would be needed to provide more customized support beyond what a standard USB HID device can offer and in addition the driver could be able to unlock the additional functionality of the controller such as the touchpad that are not supported. We suspect that an official driver will materialize at some point in the future, but we doubt Sony will be the source of it.
See the confirmation here.