net: dsa: mv88e6xxx: Only allow LAG offload on supported hardware

There are chips that do have Global 2 registers, and therefore trunk
mapping/mask tables are not available. Refuse the offload as early as
possible on those devices.

Fixes: 57e661aae6 ("net: dsa: mv88e6xxx: Link aggregation support")
Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -5385,9 +5385,13 @@ static bool mv88e6xxx_lag_can_offload(struct dsa_switch *ds,
 				      struct net_device *lag,
 				      struct netdev_lag_upper_info *info)
 {
+	struct mv88e6xxx_chip *chip = ds->priv;
 	struct dsa_port *dp;
 	int id, members = 0;
 
+	if (!mv88e6xxx_has_lag(chip))
+		return false;
+
 	id = dsa_lag_id(ds->dst, lag);
 	if (id < 0 || id >= ds->num_lag_ids)
 		return false;
@@ -5727,7 +5731,7 @@ static int mv88e6xxx_register_switch(struct mv88e6xxx_chip *chip)
 	 * 5-bit port mode, which we do not support. 640k^W16 ought to
 	 * be enough for anyone.
 	 */
-	ds->num_lag_ids = 16;
+	ds->num_lag_ids = mv88e6xxx_has_lag(chip) ? 16 : 0;
 
 	dev_set_drvdata(dev, ds);
 

drivers/net/dsa/mv88e6xxx/chip.h

@@ -662,6 +662,11 @@ static inline bool mv88e6xxx_has_pvt(struct mv88e6xxx_chip *chip)
 	return chip->info->pvt;
 }
 
+static inline bool mv88e6xxx_has_lag(struct mv88e6xxx_chip *chip)
+{
+	return !!chip->info->global2_addr;
+}
+
 static inline unsigned int mv88e6xxx_num_databases(struct mv88e6xxx_chip *chip)
 {
 	return chip->info->num_databases;