How to operate the SMI(MDIO) bus of Xavier

I replace the PHY of Xavier carrier board with a Switch in a new design,and I want to operate the SMI(MDC,MDIO) bus to read/write the register of Switch,how to do this,and where can I operate it?
Thanks!

Please refer to this topic: https://devtalk.nvidia.com/default/topic/1055504/jetson-agx-xavier/net-dsa-switch-can-t-work-/