AM335x CPGMAC_SL MAC CONTROL REGISTER

Hello Will,

These registers are used internally by the CPSW IP to control multiple interface gaskets to a SoC if needed. In the case of AM335x, the SoC presents a single internal interface per sliver (GMII to RMII in this case) so IFCTL_B is not needed. 

As I recall, the Linux driver just sets both regardless of SoC architecture as a way to enable SW re-use.