A patch for 3.5 kernel to provide jumbo frame support for CuBox from Rabeeh Khoury's 2.6.32-9 fork Update to current git diff as of Nov 8, 2013 from https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git This is against v3.12 branch.

mv643xx_eth.c.patch

diff --git a/drivers/net/ethernet/marvell/mv643xx_eth.c b/drivers/net/ethernet/marvell/mv643xx_eth.c
index 2c210ec..528770b 100644
--- a/drivers/net/ethernet/marvell/mv643xx_eth.c
+++ b/drivers/net/ethernet/marvell/mv643xx_eth.c
@@ -2333,6 +2333,13 @@ static int mv643xx_eth_change_mtu(struct net_device *dev, int new_mtu)
 	dev->mtu = new_mtu;
 	mv643xx_eth_recalc_skb_size(mp);
 	tx_set_rate(mp, 1000000000, 16777216);
+	if (dev->mtu > 1600) {
+		dev->features &= ~NETIF_F_IP_CSUM;
+		dev->vlan_features &= ~NETIF_F_IP_CSUM;
+	} else {
+		dev->features |= NETIF_F_IP_CSUM;
+		dev->vlan_features |= NETIF_F_IP_CSUM;
+	}
 
 	if (!netif_running(dev))
 		return 0;

The Marvell chip on Cubox supports jumbo frame but it only supports hardware checksum offload up to 1600 mtu. That is why we need to disable hardware checksum when mtu is greater than 1600.

Interweb discussion:
https://groups.google.com/forum/#!topic/linux.debian.ports.arm/bPrwvTxRQQc
http://comments.gmane.org/gmane.linux.ports.arm.kernel/178785