net: ftgmac100: Always register the MDIO bus when it exists

Both the Aspeed 2400 and 2500 and the original faraday version of the
MAC have MDIO bus controllers as part of the MAC. Since it exists,
always registering it makes the code simpler, and causes no harm. If
there is no mdio node in device tree, of_mdiobus_register() will fall
back to mdiobus_register(), making it safe.

AST2600 uses an external MDIO controller and does not have an embedded
MDIO bus in the MAC. For such configurations, the legacy MII probe path
must not be entered without a registered mii_bus.

Add an explicit check to fail gracefully when no MDIO bus is present,
preventing a NULL pointer dereference while keeping the intended
behavior for platforms without embedded MDIO.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Jacky Chou <jacky_chou@aspeedtech.com>
Link: https://patch.msgid.link/20260206-ftgmac-cleanup-v5-9-ad28a9067ea7@aspeedtech.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: lunn

drivers/net/ethernet/faraday/ftgmac100.c

@@ -1483,6 +1483,11 @@ static int ftgmac100_mii_probe(struct net_device *netdev)
 	phy_interface_t phy_intf;
 	int err;
 
+	if (!priv->mii_bus) {
+		dev_err(priv->dev, "No MDIO bus available\n");
+		return -ENODEV;
+	}
+
 	/* Default to RGMII. It's a gigabit part after all */
 	err = of_get_phy_mode(np, &phy_intf);
 	if (err)
@@ -1968,32 +1973,28 @@ static int ftgmac100_probe(struct platform_device *pdev)
 		priv->txdes0_edotr_mask = BIT(15);
 	}
 
+	if (priv->mac_id == FTGMAC100_FARADAY ||
+	    priv->mac_id == FTGMAC100_AST2400 ||
+	    priv->mac_id == FTGMAC100_AST2500) {
+		err = ftgmac100_setup_mdio(netdev);
+		if (err)
+			return err;
+	}
+
 	if (np && of_get_property(np, "use-ncsi", NULL)) {
 		err = ftgmac100_probe_ncsi(netdev, priv, pdev);
 		if (err)
-			goto err_setup_mdio;
+			goto err;
 	} else if (np && (of_phy_is_fixed_link(np) ||
 			  of_get_property(np, "phy-handle", NULL))) {
 		struct phy_device *phy;
 
-		/* Support "mdio"/"phy" child nodes for ast2400/2500 with
-		 * an embedded MDIO controller. Automatically scan the DTS for
-		 * available PHYs and register them.
-		 */
-		if (of_get_property(np, "phy-handle", NULL) &&
-		    (priv->mac_id == FTGMAC100_AST2400 ||
-		     priv->mac_id == FTGMAC100_AST2500)) {
-			err = ftgmac100_setup_mdio(netdev);
-			if (err)
-				goto err_setup_mdio;
-		}
-
 		phy = of_phy_get_and_connect(priv->netdev, np,
 					     &ftgmac100_adjust_link);
 		if (!phy) {
 			dev_err(&pdev->dev, "Failed to connect to phy\n");
 			err = -EINVAL;
-			goto err_phy_connect;
+			goto err;
 		}
 
 		/* Indicate that we support PAUSE frames (see comment in
@@ -2010,28 +2011,25 @@ static int ftgmac100_probe(struct platform_device *pdev)
 		 * PHYs.
 		 */
 		priv->use_ncsi = false;
-		err = ftgmac100_setup_mdio(netdev);
-		if (err)
-			goto err_setup_mdio;
 
 		err = ftgmac100_mii_probe(netdev);
 		if (err) {
 			dev_err(priv->dev, "MII probe failed!\n");
-			goto err_ncsi_dev;
+			goto err;
 		}
 
 	}
 
 	priv->rst = devm_reset_control_get_optional_exclusive(priv->dev, NULL);
 	if (IS_ERR(priv->rst)) {
 		err = PTR_ERR(priv->rst);
-		goto err_phy_connect;
+		goto err;
 	}
 
 	if (priv->is_aspeed) {
 		err = ftgmac100_setup_clk(priv);
 		if (err)
-			goto err_phy_connect;
+			goto err;
 
 		/* Disable ast2600 problematic HW arbitration */
 		if (priv->mac_id == FTGMAC100_AST2600)
@@ -2067,21 +2065,18 @@ static int ftgmac100_probe(struct platform_device *pdev)
 	err = register_netdev(netdev);
 	if (err) {
 		dev_err(&pdev->dev, "Failed to register netdev\n");
-		goto err_register_netdev;
+		goto err;
 	}
 
 	netdev_info(netdev, "irq %d, mapped at %p\n", netdev->irq, priv->base);
 
 	return 0;
 
-err_register_netdev:
-err_phy_connect:
+err:
 	ftgmac100_phy_disconnect(netdev);
-err_ncsi_dev:
 	if (priv->ndev)
 		ncsi_unregister_dev(priv->ndev);
 	ftgmac100_destroy_mdio(netdev);
-err_setup_mdio:
 	return err;
 }