stmmac: add fixed-link device-tree support

In case DT is used, this change adds the ability to the stmmac driver to
detect a fixed-link PHY, instanciate it, and use it during
phy_connect().

Fixed link PHYs DT usage is described in:
Documentation/devicetree/bindings/net/fixed-link.txt

Signed-off-by: Mathieu Olivari <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

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

···
 	 * device as well.
 	 * Note: phydev->phy_id is the result of reading the UID PHY registers.
 	 */
-	if (phydev->phy_id == 0) {
+	if (!priv->plat->phy_node && phydev->phy_id == 0) {
 		phy_disconnect(phydev);
 		return -ENODEV;
 	}

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

···
 	/* If we find a phy-handle property, use it as the PHY */
 	plat->phy_node = of_parse_phandle(np, "phy-handle", 0);
 
+	/* If phy-handle is not specified, check if we have a fixed-phy */
+	if (!plat->phy_node && of_phy_is_fixed_link(np)) {
+		if ((of_phy_register_fixed_link(np) < 0))
+			return -ENODEV;
+
+		plat->phy_node = of_node_get(np);
+	}
+
 	/* "snps,phy-addr" is not a standard property. Mark it as deprecated
 	 * and warn of its use. Remove this when phy node support is added.
 	 */
···
 	if (of_find_property(np, "snps,pbl", NULL)) {
 		dma_cfg = devm_kzalloc(&pdev->dev, sizeof(*dma_cfg),
 				       GFP_KERNEL);
-		if (!dma_cfg)
+		if (!dma_cfg) {
+			of_node_put(np);
 			return -ENOMEM;
+		}
 		plat->dma_cfg = dma_cfg;
 		of_property_read_u32(np, "snps,pbl", &dma_cfg->pbl);
 		dma_cfg->fixed_burst =