net: dsa: vsc73xx: make the MTU configurable

Instead of hardcoding the MTU to the maximum value allowed by the
hardware, obey the value known by the operating system.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/vitesse-vsc73xx-core.c

@@ -664,16 +664,6 @@ static void vsc73xx_init_port(struct vsc73xx *vsc, int port)
 		      VSC73XX_MAC_CFG_TX_EN |
 		      VSC73XX_MAC_CFG_RX_EN);
 
-	/* Max length, we can do up to 9.6 KiB, so allow that.
-	 * According to application not "VSC7398 Jumbo Frames" setting
-	 * up the MTU to 9.6 KB does not affect the performance on standard
-	 * frames, so just enable it. It is clear from the application note
-	 * that "9.6 kilobytes" == 9600 bytes.
-	 */
-	vsc73xx_write(vsc, VSC73XX_BLOCK_MAC,
-		      port,
-		      VSC73XX_MAXLEN, 9600);
-
 	/* Flow control for the CPU port:
 	 * Use a zero delay pause frame when pause condition is left
 	 * Obey pause control frames
@@ -1030,6 +1020,24 @@ static void vsc73xx_get_ethtool_stats(struct dsa_switch *ds, int port,
 	}
 }
 
+static int vsc73xx_change_mtu(struct dsa_switch *ds, int port, int new_mtu)
+{
+	struct vsc73xx *vsc = ds->priv;
+
+	return vsc73xx_write(vsc, VSC73XX_BLOCK_MAC, port,
+			     VSC73XX_MAXLEN, new_mtu);
+}
+
+/* According to application not "VSC7398 Jumbo Frames" setting
+ * up the MTU to 9.6 KB does not affect the performance on standard
+ * frames. It is clear from the application note that
+ * "9.6 kilobytes" == 9600 bytes.
+ */
+static int vsc73xx_get_max_mtu(struct dsa_switch *ds, int port)
+{
+	return 9600;
+}
+
 static const struct dsa_switch_ops vsc73xx_ds_ops = {
 	.get_tag_protocol = vsc73xx_get_tag_protocol,
 	.setup = vsc73xx_setup,
@@ -1041,6 +1049,8 @@ static const struct dsa_switch_ops vsc73xx_ds_ops = {
 	.get_sset_count = vsc73xx_get_sset_count,
 	.port_enable = vsc73xx_port_enable,
 	.port_disable = vsc73xx_port_disable,
+	.port_change_mtu = vsc73xx_change_mtu,
+	.port_max_mtu = vsc73xx_get_max_mtu,
 };
 
 static int vsc73xx_gpio_get(struct gpio_chip *chip, unsigned int offset)