+static int otto_emdio_notify_phy_attach(struct phy_device *phydev)
+{
+	struct otto_emdio_priv *priv = otto_emdio_bus_to_priv(phydev->mdio.bus);
+	int port = otto_emdio_phy_to_port(phydev->mdio.bus, phydev->mdio.addr);
+	int ret;
+
+	if (port < 0)
+		return port;

Here seems like a good place to check the PHY is a realtek PHY, and
return -ENODEV if not. That should cause phy_attach_direct() to fail,
making it impossible to configure the port up.

	Andrew