Das U-Boot provides a command line option for banging directly on the Media Independent Interface bus. This allows people to poke PHYs directly (presumably for debugging purposes) via supported Ethernet MACs.
Note that not all Ethernet MAC drivers in U-Boot support the MDIO functions. The Blackfin EMAC driver does support it.
In your board config, you simply need to enable:
bfin> help mii mii - MII utility commands Usage: mii device - list available devices mii device <devname> - set current device mii info <addr> - display MII PHY info mii read <addr> <reg> - read MII PHY <addr> register <reg> mii write <addr> <reg> <data> - write MII PHY <addr> register <reg> mii dump <addr> <reg> - pretty-print <addr> <reg> (0-5 only) Addr and/or reg may be ranges, e.g. 2-7.
You first have to find a supported device, and then you have to select it. The first ethernet driver is selected by default.
bfin> mii device MII devices: 'Blackfin EMAC' Current device: 'Blackfin EMAC'
We can query the PHY at address 1:
bfin> mii info 1 PHY 0x01: OUI = 0x01F0, Model = 0x0A, Rev = 0x03, 10baseT, FDX
We can read registers directly from different PHYs. Here we read registers 0 through 4 from the PHY at address 1:
bfin> mii read 1 0 1000 bfin> mii read 1 1 782D bfin> mii read 1 2 0007 bfin> mii read 1 3 C0A3 bfin> mii read 1 4 0DE1
Conversely, you can use
mii write to program hex values directly into specific PHY registers.