net: dsa: mt7530: improve code path for setting up port 5

There're two code paths for setting up port 5:

mt7530_setup()
-> mt7530_setup_port5()

mt753x_phylink_mac_config()
-> mt753x_mac_config()
   -> mt7530_mac_config()
      -> mt7530_setup_port5()

Currently mt7530_setup_port5() from mt7530_setup() always runs. If port 5
is used as a CPU, DSA, or user port, mt7530_setup_port5() from
mt753x_phylink_mac_config() won't run. That is because priv->p5_interface
set on mt7530_setup_port5() will match state->interface on
mt753x_phylink_mac_config() which will stop running mt7530_setup_port5()
again.

Therefore, mt7530_setup_port5() will never run from
mt753x_phylink_mac_config().

Address this by not running mt7530_setup_port5() from mt7530_setup() if
port 5 is used as a CPU, DSA, or user port. This driver isn't in the
dsa_switches_apply_workarounds[] array so phylink will always be present.

To keep the cases where port 5 isn't controlled by phylink working as
before, preserve the mt7530_setup_port5() call from mt7530_setup().

Do not set priv->p5_intf_sel to P5_DISABLED. It is already set to that when
"priv" is allocated.

Move setting the interface to a more specific location. It's supposed to be
overwritten if PHY muxing is detected.

Improve the comment which explains the process.
Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20240122-for-netnext-mt7530-improvements-1-v3-5-042401f2b279@arinc9.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/mt7530.c

@@ -2326,16 +2326,15 @@ mt7530_setup(struct dsa_switch *ds)
 		return ret;
 
 	/* Setup port 5 */
-	priv->p5_intf_sel = P5_DISABLED;
-	interface = PHY_INTERFACE_MODE_NA;
-
 	if (!dsa_is_unused_port(ds, 5)) {
 		priv->p5_intf_sel = P5_INTF_SEL_GMAC5;
-		ret = of_get_phy_mode(dsa_to_port(ds, 5)->dn, &interface);
-		if (ret && ret != -ENODEV)
-			return ret;
 	} else {
-		/* Scan the ethernet nodes. look for GMAC1, lookup used phy */
+		/* Scan the ethernet nodes. Look for GMAC1, lookup the used PHY.
+		 * Set priv->p5_intf_sel to the appropriate value if PHY muxing
+		 * is detected.
+		 */
+		interface = PHY_INTERFACE_MODE_NA;
+
 		for_each_child_of_node(dn, mac_np) {
 			if (!of_device_is_compatible(mac_np,
 						     "mediatek,eth-mac"))
@@ -2366,6 +2365,8 @@ mt7530_setup(struct dsa_switch *ds)
 			of_node_put(phy_node);
 			break;
 		}
+
+		mt7530_setup_port5(ds, interface);
 	}
 
 #ifdef CONFIG_GPIOLIB
@@ -2376,8 +2377,6 @@ mt7530_setup(struct dsa_switch *ds)
 	}
 #endif /* CONFIG_GPIOLIB */
 
-	mt7530_setup_port5(ds, interface);
-
 	/* Flush the FDB table */
 	ret = mt7530_fdb_cmd(priv, MT7530_FDB_FLUSH, NULL);
 	if (ret < 0)