QCA808x does not currently fill in the possible_interfaces.
This leads to Phylink not being aware that it supports 2500Base-X as well
so in cases where it is connected to a DSA switch like MV88E6393 it will
limit that port to phy-mode set in the DTS.
That means that if SGMII is used you are limited to 1G only while if
2500Base-X was set you are limited to 2.5G only.
Populating the possible_interfaces fixes this, so lets backport the patches
from kernel 6.9.
This also includes a backport of the Phylink PHY validation series from
kernel 6.8 that allows the use of possible_interfaces.
Link: https://github.com/openwrt/openwrt/pull/15765
Signed-off-by: Robert Marko <robimarko@gmail.com>
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