CONFIG_MDIO_BUS_MUX (not configurable)

modulename: mdio-mux.ko

configname: CONFIG_MDIO_BUS_MUX

Linux Kernel Configuration
└─>Device Drivers
└─>Network device support
└─>PHY Device support and infrastructure
└─>MDIO_BUS_MUX
In linux kernel since version 3.1 (release Date: 2011-10-24)  
This module provides a driver framework for MDIO bus
multiplexers which connect one of several child MDIO busses
to a parent bus. Switching between child busses is done by
device specific drivers.

source code:
drivers/net/phy/mdio-mux.c