quoted

drivers/ptp/core    - API as written above
drivers/ptp/virtual - all PtP drivers somehow emulating a PtP clock
                       (like the ptp_s390 driver)
drivers/ptp/net     - all NIC related drivers.

Well, drivers/ptp/virtual is not really good, because some drivers are
for physical devices exporting PTP interface, but without NIC.

If the lack of a NIC is the differentiating property:

quoted

drivers/ptp/net     - all NIC related drivers.
drivers/ptp/netless - all related drivers which are not associated to a NIC.

Or

quoted

drivers/ptp/emulating - all drivers emulating a PtP clock

	Andrew