net: dsa: qca8k: drop MTU tracking from qca8k_priv

DSA set the CPU port based on the largest MTU of all the slave ports.
Based on this we can drop the MTU array from qca8k_priv and set the
port_change_mtu logic on DSA changing MTU of the CPU port as the switch
have a global MTU settingfor each port.
Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/qca8k.c

@@ -2367,16 +2367,18 @@ static int
 qca8k_port_change_mtu(struct dsa_switch *ds, int port, int new_mtu)
 {
 	struct qca8k_priv *priv = ds->priv;
-	int i, mtu = 0;
 
-	priv->port_mtu[port] = new_mtu;
-
-	for (i = 0; i < QCA8K_NUM_PORTS; i++)
-		if (priv->port_mtu[i] > mtu)
-			mtu = priv->port_mtu[i];
+	/* We have only have a general MTU setting.
+	 * DSA always set the CPU port's MTU to the largest MTU of the slave
+	 * ports.
+	 * Setting MTU just for the CPU port is sufficient to correctly set a
+	 * value for every port.
+	 */
+	if (!dsa_is_cpu_port(ds, port))
+		return 0;
 
 	/* Include L2 header / FCS length */
-	return qca8k_write(priv, QCA8K_MAX_FRAME_SIZE, mtu + ETH_HLEN + ETH_FCS_LEN);
+	return qca8k_write(priv, QCA8K_MAX_FRAME_SIZE, new_mtu + ETH_HLEN + ETH_FCS_LEN);
 }
 
 static int
@@ -3033,16 +3035,6 @@ qca8k_setup(struct dsa_switch *ds)
 				  QCA8K_PORT_HOL_CTRL1_WRED_EN,
 				  mask);
 		}
-
-		/* Set initial MTU for every port.
-		 * We have only have a general MTU setting. So track
-		 * every port and set the max across all port.
-		 * Set per port MTU to 1500 as the MTU change function
-		 * will add the overhead and if its set to 1518 then it
-		 * will apply the overhead again and we will end up with
-		 * MTU of 1536 instead of 1518
-		 */
-		priv->port_mtu[i] = ETH_DATA_LEN;
 	}
 
 	/* Special GLOBAL_FC_THRESH value are needed for ar8327 switch */

drivers/net/dsa/qca8k.h

@@ -398,7 +398,6 @@ struct qca8k_priv {
 	struct device *dev;
 	struct dsa_switch_ops ops;
 	struct gpio_desc *reset_gpio;
-	unsigned int port_mtu[QCA8K_NUM_PORTS];
 	struct net_device *mgmt_master; /* Track if mdio/mib Ethernet is available */
 	struct qca8k_mgmt_eth_data mgmt_eth_data;
 	struct qca8k_mib_eth_data mib_eth_data;