net: stmmac: Add DW XPCS specified via "pcs-handle" support

Recently the DW XPCS DT-bindings have been introduced and the DW XPCS
driver has been altered to support the DW XPCS registered as a platform
device. In order to have the DW XPCS DT-device accessed from the STMMAC
driver let's alter the STMMAC PCS-setup procedure to support the
"pcs-handle" property containing the phandle reference to the DW XPCS
device DT-node. The respective fwnode will be then passed to the
xpcs_create_fwnode() function which in its turn will create the DW XPCS
descriptor utilized in the main driver for the PCS-related setups.
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c

@@ -497,15 +497,22 @@ int stmmac_mdio_reset(struct mii_bus *bus)
 
 int stmmac_pcs_setup(struct net_device *ndev)
 {
+	struct fwnode_handle *devnode, *pcsnode;
 	struct dw_xpcs *xpcs = NULL;
 	struct stmmac_priv *priv;
 	int addr, mode, ret;
 
 	priv = netdev_priv(ndev);
 	mode = priv->plat->phy_interface;
+	devnode = priv->plat->port_node;
 
 	if (priv->plat->pcs_init) {
 		ret = priv->plat->pcs_init(priv);
+	} else if (fwnode_property_present(devnode, "pcs-handle")) {
+		pcsnode = fwnode_find_reference(devnode, "pcs-handle", 0);
+		xpcs = xpcs_create_fwnode(pcsnode, mode);
+		fwnode_handle_put(pcsnode);
+		ret = PTR_ERR_OR_ZERO(xpcs);
 	} else if (priv->plat->mdio_bus_data &&
 		   priv->plat->mdio_bus_data->pcs_mask) {
 		addr = ffs(priv->plat->mdio_bus_data->pcs_mask) - 1;
@@ -515,10 +522,8 @@ int stmmac_pcs_setup(struct net_device *ndev)
 		return 0;
 	}
 
-	if (ret) {
-		dev_warn(priv->device, "No xPCS found\n");
-		return ret;
-	}
+	if (ret)
+		return dev_err_probe(priv->device, ret, "No xPCS found\n");
 
 	priv->hw->xpcs = xpcs;