I can not answer any of your questions related to the driver code, but want provide a comment related to the hardware.
Silicon revision 1.0 AM335x devices turned on internal delay mode in the transmit data path by default. However, this function was never planned to be supported in AM335x since internal timing paths in the mode were not validated during design. The default value was changed on silicon revision 2.x devices to turn this unsupported mode off. You need to make sure you have the internal delay in AM335x turned off and turn on the appropriate delay in the PHY to match your PCB board delays.
Regards,
Paul