realtek: dsa: track the primary port of a LAG

The first member of a LAG becomes its primary port when lag_primary[]
holds -1, but the array comes zero-filled from devm_kzalloc() and is
never set to -1. Every member is therefore marked non-primary, and the
FDB and MDB code of the RTL83xx skips non-primary ports.

The leave path is wrong as well: it elects a new primary whenever any
member leaves, uses fls64(), which is one-based, as a port number, and
keeps the old primary when the last member leaves, so the next LAG with
that id starts without one.

Set every slot to -1 at probe, record the primary only after the
hardware join succeeded, and on leave elect a new primary only when the
primary itself leaves: the lowest remaining member, or -1 when the LAG
is empty.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Quinn O'Shea <qoshea@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/25792
Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>

target/linux/realtek/files-6.18/drivers/net/dsa/rtl83xx/common.c

@@ -439,6 +439,7 @@ static int rtl83xx_sw_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	priv->r = r;
+	memset(priv->lag_primary, -1, sizeof(priv->lag_primary));
 
 	priv->l2_uc_map = devm_kcalloc(dev, r->fib_entries, sizeof(*priv->l2_uc_map),
 				       GFP_KERNEL);

target/linux/realtek/files-6.18/drivers/net/dsa/rtl83xx/dsa.c

@@ -1422,19 +1422,19 @@ static int rtldsa_port_lag_join(struct dsa_switch *ds,
 
 	pr_info("port_lag_join: group %d, port %d\n", group, port);
 
+	err = otto_lag_add(priv->ds, group, port, info);
+	if (err) {
+		err = -EINVAL;
+		goto out;
+	}
+
 	if (priv->lag_primary[group] == -1)
 		priv->lag_primary[group] = port;
 	else
 		priv->lag_non_primary |= BIT_ULL(port);
 
 	priv->lagmembers |= BIT_ULL(port);
-
 	pr_debug("lag_members = %llX\n", priv->lagmembers);
-	err = otto_lag_add(priv->ds, group, port, info);
-	if (err) {
-		err = -EINVAL;
-		goto out;
-	}
 
 out:
 	mutex_unlock(&priv->reg_mutex);
@@ -1466,12 +1466,12 @@ static int rtldsa_port_lag_leave(struct dsa_switch *ds, int port,
 		goto out;
 	}
 
-	/* To re-elect primary interface, just remove the first interface in
-	 * this-group's interfaces from non-primary
-	 */
-	if (priv->lags_port_members[group]) {
-		priv->lag_primary[group] = fls64(priv->lags_port_members[group]);
-		priv->lag_non_primary &= ~BIT_ULL(priv->lag_primary[group]);
+	if (priv->lag_primary[group] == port) {
+		u64 members = priv->lags_port_members[group];
+
+		priv->lag_primary[group] = members ? __ffs64(members) : -1;
+		if (members)
+			priv->lag_non_primary &= ~BIT_ULL(priv->lag_primary[group]);
 	}
 
 	/* No need to update fdb entries since they make use of trunk_id for entry.

target/linux/realtek/files-6.18/drivers/net/dsa/rtl83xx/rtl-otto.h

@@ -507,7 +507,7 @@ struct rtl838x_switch_priv {
 	/** @lag_primary: port of a LAG is primary (repesenting) and is added to
 	 * the port matrix
 	 */
-	u32 lag_primary[MAX_LAGS];
+	int lag_primary[MAX_LAGS];
 
 	/**
 	 * @lag_non_primary: Port (bit) is part of any LAG but not the