Suspend the MAC in a PHY
Set the PowerSavingControlBits bit 26 and calculate bit 25
Unset bit 0 in MMIO offset 0x120
Do a dummy read on MMIO offset 0x128
Spinwait until the "Ready" bit is set in the General Interrupt (MMIO offset 0x128) is set (up to 35 mSec, check every 10 uSec)