question about nic driver implementation(about TCP checksum offload )

Hi All: I want to build TOE(tcp checksum offload engine) in our hardware to improve the overall performance of NIC, however, i met a problem as follow: AS you know, the TCP checksum protect the TCP pseudo header+TCP header+Data, if TCP packet is fragmented into many fragments, the hardware will have not enough information to generate tcp checksum for the whole TCP PDU, how to overcome this problem? I searched in NIC driver source code of different vendor, found that TOE is generally used, I wonder whether the kernel will calculate the TCP checksum even we set features of this device as NETIF_F_IP_CSUM when fragmentation happens. Can anyone throw some lights on this problem? Thanks a lot. Rick.