net: dsa: hellcreek: Add STP forwarding rule

Treat STP as management traffic. STP traffic is designated for the CPU port
only. In addition, STP traffic has to pass blocked ports.

Fixes: e4b27ebc ("net: dsa: Add DSA driver for Hirschmann Hellcreek switches")
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/hirschmann/hellcreek.c

@@ -1075,6 +1075,17 @@ static int hellcreek_setup_fdb(struct hellcreek *hellcreek)
 		.reprio_tc    = 6,	/* TC: 6 as per IEEE 802.1AS */
 		.reprio_en    = 1,
 	};
+	static struct hellcreek_fdb_entry stp = {
+		/* MAC: 01-80-C2-00-00-00 */
+		.mac	      = { 0x01, 0x80, 0xc2, 0x00, 0x00, 0x00 },
+		.portmask     = 0x03,	/* Management ports */
+		.age	      = 0,
+		.is_obt	      = 0,
+		.pass_blocked = 1,
+		.is_static    = 1,
+		.reprio_tc    = 6,
+		.reprio_en    = 1,
+	};
 	int ret;
 
 	mutex_lock(&hellcreek->reg_lock);
@@ -1082,6 +1093,9 @@ static int hellcreek_setup_fdb(struct hellcreek *hellcreek)
 	if (ret)
 		goto out;
 	ret = __hellcreek_fdb_add(hellcreek, &p2p);
+	if (ret)
+		goto out;
+	ret = __hellcreek_fdb_add(hellcreek, &stp);
 out:
 	mutex_unlock(&hellcreek->reg_lock);