My MDIO is acting strange

[Peter Pan]

I'm porting Linux 2.6.32.6 to my MPC8247 based board. Our FCC1 and
FCC2 are used as 100MBps ethernet ports. MDIO is used to connect with
PHY chip. During boot, the of driver is checking the PHYID, it gets
all Fs. But after I comment the following lines:
//if ((phy_id & 0x1fffffff) == 0x1fffffff)
//    return NULL;
I can use my FCC ethernet normally after boot into console.
I checked that while boot, all the read bit from MDIO pin is 1, that
makes no TA bit, and no PHYID.
I'm wondering why is that happening.