net: phy: aquantia: allow forcing order of MDI pairs

net: phy: aquantia: allow forcing order of MDI pairs

Despite supporting Auto MDI-X, it looks like Aquantia only supports
swapping pair (1,2) with pair (3,6) like it used to be for MDI-X on
100MBit/s networks.

When all 4 pairs are in use (for 1000MBit/s or faster) the link does not
come up with pair order is not configured correctly, either using
MDI_CFG pin or using the "PMA Receive Reserved Vendor Provisioning 1"
register.

Normally, the order of MDI pairs being either ABCD or DCBA is configured
by pulling the MDI_CFG pin.

However, some hardware designs require overriding the value configured
by that bootstrap pin. The PHY allows doing that by setting a bit in
"PMA Receive Reserved Vendor Provisioning 1" register which allows
ignoring the state of the MDI_CFG pin and another bit configuring
whether the order of MDI pairs should be normal (ABCD) or reverse
(DCBA). Pair polarity is not affected and remains identical in both
settings.

Introduce property "marvell,mdi-cfg-order" which allows forcing either
normal or reverse order of the MDI pairs from DT.

If the property isn't present, the behavior is unchanged and MDI pair
order configuration is untouched (ie. either the result of MDI_CFG pin
pull-up/pull-down, or pair order override already configured by the
bootloader before Linux is started).

Forcing normal pair order is required on the Adtran SDG-8733A Wi-Fi 7
residential gateway.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/9ed760ff87d5fc456f31e407ead548bbb754497d.1728058550.git.daniel@makrotopia.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>