uboot下有一个mii命令。命令帮助信息如下：

mii - MII utility commands                                                      
                                                                                
Usage:                                                                          
mii device                     - list available devices                         
mii device            - set current device                             
mii info                 - display MII PHY info                           
mii read            - read  MII PHY  register             
mii write     - write MII PHY  register             
mii dump            - pretty-print   (0-5 only)           
Addr and/or reg may be ranges, e.g. 2-7. 

mii device示例，会输出MDC/MDIO总线设备

uboot>mii device                                                           
MII devices: 'FSL_MDIO0' 'FM_TGEC_MDIO'
Current device: 'FSL_MDIO0'

mii info打印输出，PHY后面跟的就是addr

uboot> mii info
PHY 0x00: OUI = 0x5043, Model = 0x1D, Rev = 0x01, 1000baseT, FDX
PHY 0x01: OUI = 0x0000, Model = 0x00, Rev = 0x00,  10baseT, HDX
PHY 0x02: OUI = 0x0000, Model = 0x00, Rev = 0x00,  10baseT, HDX
PHY 0x03: OUI = 0x0000, Model = 0x00, Rev = 0x00,  10baseT, HDX
PHY 0x04: OUI = 0x0000, Model = 0x00, Rev = 0x00,  10baseT, HDX
PHY 0x05: OUI = 0x0000, Model = 0x00, Rev = 0x00,  10baseT, HDX
PHY 0x06: OUI = 0x0000, Model = 0x00, Rev = 0x00,  10baseT, HDX
PHY 0x07: OUI = 0x0000, Model = 0x00, Rev = 0x00,  10baseT, HDX

mii read          - read  MII PHY register            
mii write   - write MII PHY register  

上述两个命令，需要根据具体的芯片手册寄存器设置来进行配置。以下命令为示例

mii write 0 0 0x8000    向地址为0的phy芯片的0寄存器写入0x8000

mii  read 0 0     读取地址为0的phy芯片的寄存器0的值