TDA4VM: HOW CPSW9G MDIO state machine work?

Part Number: TDA4VM

Hi Experts:

        i use the bcm89811 net phy, i read the phy register by mdio, It's on the link up， but the CPSW_SS_RGMII5_STATUS_REG  show the link is down ，enble the CPSW_MDIO_CONTROL_RE‘s 30bit，it will enable theMDIO state machine. 

        my questions is :

       1, how the MDIO state machine work? 

       2，how the mac get the link status？Is mac automatically reading the 0x01 register data of phy to get the status?

The meaning of bcm89811‘s register 0x01 is as follows。i use the psdk 7.0，I use my own board. The last version board used the phy of dp83867, which works normally. The hardware version of this one is only changed to a PHY, and there are no other changes.

Thanks.