net: dsa: mv88e6xxx: Hold mutex while doing stats operations

Until now, there has been no need to hold the reg mutex while getting
the count of statistics, or the strings, because the hardware was not
accessed. When adding support for SERDES statistics, it is necessary
to access the hardware, to determine if a port is using the SERDES
interface. So add mutex lock/unlocks.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -724,8 +724,12 @@ static void mv88e6xxx_get_strings(struct dsa_switch *ds, int port,
 {
 	struct mv88e6xxx_chip *chip = ds->priv;
 
+	mutex_lock(&chip->reg_lock);
+
 	if (chip->info->ops->stats_get_strings)
 		chip->info->ops->stats_get_strings(chip, data);
+
+	mutex_unlock(&chip->reg_lock);
 }
 
 static int mv88e6xxx_stats_get_sset_count(struct mv88e6xxx_chip *chip,
@@ -757,11 +761,14 @@ static int mv88e6320_stats_get_sset_count(struct mv88e6xxx_chip *chip)
 static int mv88e6xxx_get_sset_count(struct dsa_switch *ds, int port)
 {
 	struct mv88e6xxx_chip *chip = ds->priv;
+	int ret = 0;
 
+	mutex_lock(&chip->reg_lock);
 	if (chip->info->ops->stats_get_sset_count)
-		return chip->info->ops->stats_get_sset_count(chip);
+		ret = chip->info->ops->stats_get_sset_count(chip);
+	mutex_unlock(&chip->reg_lock);
 
-	return 0;
+	return ret;
 }
 
 static void mv88e6xxx_stats_get_stats(struct mv88e6xxx_chip *chip, int port,