Thanks for jumping in. We are using BCM5389 and the MDIO bus is used to
access BCM5389 MDC/MDIO interface in Pseudo-PHY mode.

I didn't know drivers/net/dsa, but let me check out the drivers and see
if it works in the Cloudripper environment.

The b53 driver knows about this switch, so please make use of that
driver. See Documentation/devicetree/bindings/net/dsa/brcm,b53.yaml
for how you describe it in DT.

    Andrew