At the moment, mEMACs are configured almost completely based on the
phy-connection-type. That is, if the phy interface is RGMII, it assumed
that RGMII is supported. For some interfaces, it is assumed that the
RCW/bootloader has set up the SerDes properly. This is generally OK, but
restricts runtime reconfiguration. The actual link state is never
reported.

To address these shortcomings, the driver will need additional
information. First, it needs to know how to access the PCS/PMAs (in
order to configure them and get the link status). The SGMII PCS/PMA is
the only currently-described PCS/PMA. Add the XFI and QSGMII PCS/PMAs as
well. The XFI (and 10GBASE-KR) PCS/PMA is a c45 "phy" which sits on the
same MDIO bus as SGMII PCS/PMA. By default they will have conflicting
addresses, but they are also not enabled at the same time by default.
Therefore, we can let the XFI PCS/PMA be the default when
phy-connection-type is xgmii. This will allow for
backwards-compatibility.

QSGMII, however, cannot work with the current binding. This is because
the QSGMII PCS/PMAs are only present on one MAC's MDIO bus. At the
moment this is worked around by having every MAC write to the PCS/PMA
addresses (without checking if they are present). This only works if
each MAC has the same configuration, and only if we don't need to know
the status. Because the QSGMII PCS/PMA will typically be located on a
different MDIO bus than the MAC's SGMII PCS/PMA, there is no fallback
for the QSGMII PCS/PMA.
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>