Pcie c4 and c0 are set to ep mode at the same time for AGX Xavier

Our carrier board want to use pcie c0, pcie c4 as endpoint mode as one board and use at the same time
We found in the OEM manual that there are NVHS0_SLVS_REFCLK_N/P, UPHY_
REFCLK2_N/P Three sets of reference clocks are available for input.What is the difference between these three sets of reference input clocks? How do we use these clocks?