net: dsa: microchip: fix bridging with more than two member ports

Commit b3612ccd ("net: dsa: microchip: implement multi-bridge support")
plugged a packet leak between ports that were members of different bridges.
Unfortunately, this broke another use case, namely that of more than two
ports that are members of the same bridge.

After that commit, when a port is added to a bridge, hardware bridging
between other member ports of that bridge will be cleared, preventing
packet exchange between them.

Fix by ensuring that the Port VLAN Membership bitmap includes any existing
ports in the bridge, not just the port being added.

Fixes: b3612ccd ("net: dsa: microchip: implement multi-bridge support")
Signed-off-by: Svenning Sørensen <sss@secomea.com>
Tested-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/microchip/ksz_common.c

@@ -26,7 +26,7 @@ void ksz_update_port_member(struct ksz_device *dev, int port)
 	struct dsa_switch *ds = dev->ds;
 	u8 port_member = 0, cpu_port;
 	const struct dsa_port *dp;
-	int i;
+	int i, j;
 
 	if (!dsa_is_user_port(ds, port))
 		return;
@@ -45,13 +45,33 @@ void ksz_update_port_member(struct ksz_device *dev, int port)
 			continue;
 		if (!dsa_port_bridge_same(dp, other_dp))
 			continue;
+		if (other_p->stp_state != BR_STATE_FORWARDING)
+			continue;
 
-		if (other_p->stp_state == BR_STATE_FORWARDING &&
-		    p->stp_state == BR_STATE_FORWARDING) {
+		if (p->stp_state == BR_STATE_FORWARDING) {
 			val |= BIT(port);
 			port_member |= BIT(i);
 		}
 
+		/* Retain port [i]'s relationship to other ports than [port] */
+		for (j = 0; j < ds->num_ports; j++) {
+			const struct dsa_port *third_dp;
+			struct ksz_port *third_p;
+
+			if (j == i)
+				continue;
+			if (j == port)
+				continue;
+			if (!dsa_is_user_port(ds, j))
+				continue;
+			third_p = &dev->ports[j];
+			if (third_p->stp_state != BR_STATE_FORWARDING)
+				continue;
+			third_dp = dsa_to_port(ds, j);
+			if (dsa_port_bridge_same(other_dp, third_dp))
+				val |= BIT(j);
+		}
+
 		dev->dev_ops->cfg_port_member(dev, i, val | cpu_port);
 	}