dsa: mv88e6xxx: Fix MTU definition

The MTU passed to the DSA driver is the payload size, typically 1500.
However, the switch uses the frame size when applying restrictions.
Adjust the MTU with the size of the Ethernet header and the frame
checksum. The VLAN header also needs to be included when the frame
size it per port, but not when it is global.

Fixes: 1baf0fac ("net: dsa: mv88e6xxx: Use chip-wide max frame size for MTU")
Reported by: 曹煜 <cao88yu@gmail.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -2834,8 +2834,8 @@ static int mv88e6xxx_setup_port(struct mv88e6xxx_chip *chip, int port)
 	if (err)
 		return err;
 
-	/* Port Control 2: don't force a good FCS, set the maximum frame size to
-	 * 10240 bytes, disable 802.1q tags checking, don't discard tagged or
+	/* Port Control 2: don't force a good FCS, set the MTU size to
+	 * 10222 bytes, disable 802.1q tags checking, don't discard tagged or
 	 * untagged frames on this port, do a destination address lookup on all
 	 * received packets as usual, disable ARP mirroring and don't send a
 	 * copy of all transmitted/received frames on this port to the CPU.
@@ -2854,7 +2854,7 @@ static int mv88e6xxx_setup_port(struct mv88e6xxx_chip *chip, int port)
 		return err;
 
 	if (chip->info->ops->port_set_jumbo_size) {
-		err = chip->info->ops->port_set_jumbo_size(chip, port, 10240);
+		err = chip->info->ops->port_set_jumbo_size(chip, port, 10218);
 		if (err)
 			return err;
 	}
@@ -2944,10 +2944,10 @@ static int mv88e6xxx_get_max_mtu(struct dsa_switch *ds, int port)
 	struct mv88e6xxx_chip *chip = ds->priv;
 
 	if (chip->info->ops->port_set_jumbo_size)
-		return 10240;
+		return 10240 - VLAN_ETH_HLEN - ETH_FCS_LEN;
 	else if (chip->info->ops->set_max_frame_size)
-		return 1632;
-	return 1522;
+		return 1632 - VLAN_ETH_HLEN - ETH_FCS_LEN;
+	return 1522 - VLAN_ETH_HLEN - ETH_FCS_LEN;
 }
 
 static int mv88e6xxx_change_mtu(struct dsa_switch *ds, int port, int new_mtu)

drivers/net/dsa/mv88e6xxx/global1.c

@@ -232,6 +232,8 @@ int mv88e6185_g1_set_max_frame_size(struct mv88e6xxx_chip *chip, int mtu)
 	u16 val;
 	int err;
 
+	mtu += ETH_HLEN + ETH_FCS_LEN;
+
 	err = mv88e6xxx_g1_read(chip, MV88E6XXX_G1_CTL1, &val);
 	if (err)
 		return err;

drivers/net/dsa/mv88e6xxx/port.c

@@ -1277,6 +1277,8 @@ int mv88e6165_port_set_jumbo_size(struct mv88e6xxx_chip *chip, int port,
 	u16 reg;
 	int err;
 
+	size += VLAN_ETH_HLEN + ETH_FCS_LEN;
+
 	err = mv88e6xxx_port_read(chip, port, MV88E6XXX_PORT_CTL2, &reg);
 	if (err)
 		return err;