Puzzled about MDIO issue

Hi, All I've been reading MDIO code, tiny though but it still puzzled me for its usage. MDIO is an hardware interface for the MAC to set/get PHY configuration/status. Linux manipulates MDIO through: struct net_device ->do_ioctl -> mdio_mii_ioctl -> mdio_read/mdio_write Question: A: Turn an NIC from cold state to running state, is this ioctl must be used to configure the PHY? If so , how? B: what's the usage of this net device ioctl? I found an user-space package mii-tool create a socket first and then use the socket handle for ioctl to query lots of PHY information. Is there any other typical usage of it? thanks bill