Attached is the patch for implementing 2-buffer mode on Rx path.

On certain systems when a DMA has to happen on an un-aligned memory
location performance will take a significant hit. It's standard
practice to offset the Rx buffer address by 2 (as Mac header is 14
bytes) so the IP header starts from an aligned location.  Obviously
using a single Rx buffer both cannot be achieved. Thus XFrame supports
something called 2 buffer Rx mode, where in the Rx'ed frame is split
into 2 parts, one is the Ethernet header and the other is the Ethernet
payload. So now we can allocate proper aligned memory for both buffers,
hence the DMA is not slowed down. Also, the Ethernet payload(starting
from L3 header) is on an aligned location so OS need not have to do
un-aligned accesses to process IP header. To achieve this, the kernel
function eth_type_trans functionality has to be partially implemented
in the driver itself.
Signed-off-by: Raghavendra Koushik <raghavendra.koushik@s2io.com>
Signed-off-by: Ravinandan Arakali <ravinandan.arakali@s2io.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>