XAUI allows XGMII to reach an extended distance by using a XGXS layer at
each end of the MAC to PHY link, operating over four Serdes lanes.

10GBASE-KR is a single lane Serdes backplane ethernet connection method
with autonegotiation on the link.  Some PHYs use this to connect to the
ethernet interface at 10G speeds, switching to other connection types
when utilising slower speeds.

10GBASE-KR is also used for XFI and SFI to connect to XFP and SFP fiber
modules.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>