net: dsa: mt7530: detect PHY muxing when PHY is defined on switch MDIO bus

net: dsa: mt7530: detect PHY muxing when PHY is defined on switch MDIO bus

Currently, the MT7530 DSA subdriver configures the MT7530 switch to provide
direct access to switch PHYs, meaning, the switch PHYs listen on the MDIO
bus the switch listens on. The PHY muxing feature makes use of this.

This is problematic as the PHY may be attached before the switch is
initialised, in which case, the PHY will fail to be attached.

Since commit 91374ba537bd ("net: dsa: mt7530: support OF-based registration
of switch MDIO bus"), we can describe the switch PHYs on the MDIO bus of
the switch on the device tree. Extend the check to detect PHY muxing when
the PHY is defined on the MDIO bus of the switch on the device tree.

When the PHY is described this way, the switch will be initialised first,
then the switch MDIO bus will be registered. Only after these steps, the
PHY will be attached.

Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Reviewed-by: Daniel Golle <daniel@makrotopia.org>
Link: https://lore.kernel.org/r/20240430-b4-for-netnext-mt7530-use-switch-mdio-bus-for-phy-muxing-v2-1-9104d886d0db@arinc9.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>