net: dsa: b53: add MTU configuration support

It looks like the Broadcom switches supported by the b53 driver don't
support precise configuration of the MTU, but just a mumbo-jumbo boolean
flag. Set that.

Also configure BCM583XX devices to send and receive jumbo frames when
ports are configured with 10/100 Mbps speed.

Signed-off-by: Murali Krishna Policharla <murali.policharla@broadcom.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/b53/b53_common.c

@@ -699,9 +699,6 @@ int b53_configure_vlan(struct dsa_switch *ds)
 		b53_write16(dev, B53_VLAN_PAGE,
 			    B53_VLAN_PORT_DEF_TAG(i), def_vid);
 
-	if (!is5325(dev) && !is5365(dev))
-		b53_set_jumbo(dev, dev->enable_jumbo, false);
-
 	return 0;
 }
 EXPORT_SYMBOL(b53_configure_vlan);
@@ -807,8 +804,6 @@ static int b53_phy_write16(struct dsa_switch *ds, int addr, int reg, u16 val)
 static int b53_reset_switch(struct b53_device *priv)
 {
 	/* reset vlans */
-	priv->enable_jumbo = false;
-
 	memset(priv->vlans, 0, sizeof(*priv->vlans) * priv->num_vlans);
 	memset(priv->ports, 0, sizeof(*priv->ports) * priv->num_ports);
 
@@ -2065,6 +2060,26 @@ int b53_set_mac_eee(struct dsa_switch *ds, int port, struct ethtool_eee *e)
 }
 EXPORT_SYMBOL(b53_set_mac_eee);
 
+static int b53_change_mtu(struct dsa_switch *ds, int port, int mtu)
+{
+	struct b53_device *dev = ds->priv;
+	bool enable_jumbo;
+	bool allow_10_100;
+
+	if (is5325(dev) || is5365(dev))
+		return -EOPNOTSUPP;
+
+	enable_jumbo = (mtu >= JMS_MIN_SIZE);
+	allow_10_100 = (dev->chip_id == BCM583XX_DEVICE_ID);
+
+	return b53_set_jumbo(dev, enable_jumbo, allow_10_100);
+}
+
+static int b53_get_max_mtu(struct dsa_switch *ds, int port)
+{
+	return JMS_MAX_SIZE;
+}
+
 static const struct dsa_switch_ops b53_switch_ops = {
 	.get_tag_protocol	= b53_get_tag_protocol,
 	.setup			= b53_setup,
@@ -2102,6 +2117,8 @@ static const struct dsa_switch_ops b53_switch_ops = {
 	.port_mdb_prepare	= b53_mdb_prepare,
 	.port_mdb_add		= b53_mdb_add,
 	.port_mdb_del		= b53_mdb_del,
+	.port_max_mtu		= b53_get_max_mtu,
+	.port_change_mtu	= b53_change_mtu,
 };
 
 struct b53_chip_data {