8139too: Allow setting MTU larger than 1500

Replace the default ndo_change_mtu callback with one that allow
setting MTU that the driver can handle.
Signed-off-by: Alban Bedel <albeu@free.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/realtek/8139too.c

@@ -185,6 +185,9 @@ static int debug = -1;
 /* max supported ethernet frame size -- must be at least (dev->mtu+14+4).*/
 #define MAX_ETH_FRAME_SIZE	1536
 
+/* max supported payload size */
+#define MAX_ETH_DATA_SIZE	(MAX_ETH_FRAME_SIZE - ETH_HLEN - ETH_FCS_LEN)
+
 /* Size of the Tx bounce buffers -- must be at least (dev->mtu+14+4). */
 #define TX_BUF_SIZE	MAX_ETH_FRAME_SIZE
 #define TX_BUF_TOT_LEN	(TX_BUF_SIZE * NUM_TX_DESC)
@@ -920,11 +923,19 @@ static int rtl8139_set_features(struct net_device *dev, netdev_features_t featur
 	return 0;
 }
 
+static int rtl8139_change_mtu(struct net_device *dev, int new_mtu)
+{
+	if (new_mtu < 68 || new_mtu > MAX_ETH_DATA_SIZE)
+		return -EINVAL;
+	dev->mtu = new_mtu;
+	return 0;
+}
+
 static const struct net_device_ops rtl8139_netdev_ops = {
 	.ndo_open		= rtl8139_open,
 	.ndo_stop		= rtl8139_close,
 	.ndo_get_stats64	= rtl8139_get_stats64,
-	.ndo_change_mtu		= eth_change_mtu,
+	.ndo_change_mtu		= rtl8139_change_mtu,
 	.ndo_validate_addr	= eth_validate_addr,
 	.ndo_set_mac_address 	= rtl8139_set_mac_address,
 	.ndo_start_xmit		= rtl8139_start_xmit,