Sven Auhagen reported issues with negotiation on a couple of his
platforms using a mixture of SFP and PHYs in various different
modes.  Debugging to root cause proved difficult, but essentially
the problem comes down to the mvpp2 phylink implementation being
slightly at odds with what is expected.

phylink operates in three modes: phy, fixed-link, and in-band mode.

In the first two modes, the expected behaviour from a MAC driver is
that phylink resolves the operating mode and passes the mode to the
MAC driver for it to program, including when the link should be
brought up or taken down.  This is basically the same as the libphy
approach.  This does not negate the requirement to advertise a correct
control word for interface modes that have control words where that
can be reasonably controlled.

The second mode is in-band mode, where the MAC is expected to use the
in-band control word to determine the operating mode.

The mvneta driver implements the correct pattern required to support
this: configure the port interface type separately from the in-band
mode(s).  This is now specified in the phylink documentation patches.

mvpp2 was programming in-band mode for SGMII and the 802.3z modes no
what, and avoided forcing the link up in fixed/phy modes.  This caused
a problem with some boards where the PHY is by default programmed to
enter AN bypass mode, the PHY would report that the link was up, but
the mvpp2 never completed the exchange of control word.

Another issue that mvpp2 has is it sets SGMII AN format control word
for both SGMII and 802.3z modes. The format of the control word is
defined by MVPP2_GMAC_INBAND_AN_MASK, which should be set for SGMII
and clear for 802.3z. Available Marvell documentation for earlier
GMAC implementations does not make this clear, but this has been
ascertained via extensive testing on earlier GMAC implementations,
and then confirmed with a Macchiatobin Single Shot connected to a
Clearfog: when MVPP2_GMAC_INBAND_AN_MASK is set, the clearfog does
not receive the advertised pause mode settings.

Lastly, there is no flow control in the in-band control word in Cisco
SGMII, setting the flow control autonegotiation bit even with a PHY
that has the Marvell extension to send this information does not result
in the flow control being enabled at the MAC.  We need to do this
manually using the information provided via phylink.

Re-code mvpp2's mac_config() and mac_link_up() to follow this pattern.
This allows Sven Auhagen's board and Macchiatobin to reliably bring
the link up with the 88e1512 PHY with phylink operating in PHY mode
with COMPHY built as a module but the rest of the networking built-in,
and u-boot having brought up the interface.  in-band mode requires an
additional patch to resolve another problem.
Tested-by: Sven Auhagen <sven.auhagen@voleatech.de>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>