Hi igor
Thank you for your answer, I modified the iomux_v3_cfg_t const fec2_pads[] in mx6sxsabresd.c according to this document. It still dosen't work.

I checked the value of register 2
>mii read 0x19 2
>0000
the value is wrong,and part of the sch is as follows
********************************************************
I can use the MX6_PAD_ENET1_MDC__ENET1_MDC and MX6_PAD_ENET1_MDIO__ENET1_MDIO to read the value of the register 2