How to config pcie refclk output first before installing pcie drivers

I have a situation,other soc as a pcie ep,xavier as a pcie rp.The other soc use the xavier pcie refclk.the soc starts up the pcie ep first,but the refclk has no output,so it failed to init.If the xavier starts up the pcie rp first,the pcie ep is not online that time, the xavier show the msg “link is down”,it also failed to init.So how can I let the refclk output alone, not in the pcie driver to enable it,or any oher way?