[PATCH] r8169: reduce max MTU for large frames

From: Francois Romieu <romieu@fr.zoreil.com>

The device does not support the whole mtu range it claims. Experimenting
with the Tx threshold and/or the PCI burst size does not seem to improve
the behavior.
Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>

drivers/net/r8169.c

@@ -112,7 +112,8 @@ static int multicast_filter_limit = 32;
 #define RX_DMA_BURST	6	/* Maximum PCI burst, '6' is 1024 */
 #define TX_DMA_BURST	6	/* Maximum PCI burst, '6' is 1024 */
 #define EarlyTxThld 	0x3F	/* 0x3F means NO early transmit */
-#define RxPacketMaxSize	0x3FE8	/* 16K - 1 - ETH_HLEN - VLAN - CRC */
+#define RxPacketMaxSize	0x3FE8	/* 16K - 1 - ETH_HLEN - VLAN - CRC... */
+#define SafeMtu		0x1c20	/* ... actually life sucks beyond ~7k */
 #define InterFrameGap	0x03	/* 3 means InterFrameGap = the shortest one */
 
 #define R8169_REGS_SIZE		256
@@ -1593,7 +1594,7 @@ static int rtl8169_change_mtu(struct net_device *dev, int new_mtu)
 	struct rtl8169_private *tp = netdev_priv(dev);
 	int ret = 0;
 
-	if (new_mtu < ETH_ZLEN || new_mtu > RxPacketMaxSize)
+	if (new_mtu < ETH_ZLEN || new_mtu > SafeMtu)
 		return -EINVAL;
 
 	dev->mtu = new_mtu;