net: dsa: mv88e6xxx: Enable IGMP snooping on user ports only

Do not set the MV88E6XXX_PORT_CTL0_IGMP_MLD_SNOOP bit on CPU or DSA ports.

This allows the host CPU port to be a regular IGMP listener by sending out
IGMP Membership Reports, which would otherwise not be forwarded by the
mv88exxx chip, but directly looped back to the CPU port itself.

Fixes: 54d792f2 ("net: dsa: Centralise global and port setup code into mv88e6xxx.")
Signed-off-by: Steffen Bätz <steffen@innosonix.de>
Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20230329150140.701559-1-festevam@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -3354,9 +3354,14 @@ static int mv88e6xxx_setup_port(struct mv88e6xxx_chip *chip, int port)
 	 * If this is the upstream port for this switch, enable
 	 * forwarding of unknown unicasts and multicasts.
 	 */
-	reg = MV88E6XXX_PORT_CTL0_IGMP_MLD_SNOOP |
-		MV88E6185_PORT_CTL0_USE_TAG | MV88E6185_PORT_CTL0_USE_IP |
+	reg = MV88E6185_PORT_CTL0_USE_TAG | MV88E6185_PORT_CTL0_USE_IP |
 		MV88E6XXX_PORT_CTL0_STATE_FORWARDING;
+	/* Forward any IPv4 IGMP or IPv6 MLD frames received
+	 * by a USER port to the CPU port to allow snooping.
+	 */
+	if (dsa_is_user_port(ds, port))
+		reg |= MV88E6XXX_PORT_CTL0_IGMP_MLD_SNOOP;
+
 	err = mv88e6xxx_port_write(chip, port, MV88E6XXX_PORT_CTL0, reg);
 	if (err)
 		return err;