u-boot/doc/README.fec_mxc

U-Boot config options used in fec_mxc.c

CONFIG_FEC_MXC
	Selects fec_mxc.c to be compiled into u-boot. Can read out the
	ethaddr from the SoC eFuses (see below).

CONFIG_MII
	Must be defined if CONFIG_FEC_MXC is defined.

CONFIG_FEC_XCV_TYPE
	Defaults to MII100 for 100 Base-tx.
	RGMII selects 1000 Base-tx reduced pin count interface.
	RMII selects 100 Base-tx reduced pin count interface.

CONFIG_FEC_MXC_SWAP_PACKET
	Forced on iff MX28.
	Swaps the bytes order of all words(4 byte units) in the packet.
	This should not be specified by a board file. It is cpu specific.

CONFIG_PHYLIB
	fec_mxc supports PHYLIB and should be used for new boards.

CONFIG_FEC_MXC_NO_ANEG
	Relevant only if PHYLIB not used. Skips auto-negotiation restart.

CONFIG_FEC_MXC_PHYADDR
	Optional, selects the exact phy address that should be connected
	and function fecmxc_initialize will try to initialize it.


Reading the ethaddr from the SoC eFuses:
if CONFIG_FEC_MXC is defined and the U-Boot environment does not contain the
ethaddr variable, then its value gets read from the corresponding eFuses in
the SoC. See the README files of the specific SoC for details.