[tcpip] Allow for architecture-specific TCP/IP checksum routines

Calculating the TCP/IP checksum on received packets accounts for a
substantial fraction of the response latency.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/include/bits/tcpip.h

+#ifndef _BITS_TCPIP_H
+#define _BITS_TCPIP_H
+
+/** @file
+ *
+ * Transport-network layer interface
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#endif /* _BITS_TCPIP_H */

src/include/ipxe/tcpip.h

 #include <ipxe/socket.h>
 #include <ipxe/in.h>
 #include <ipxe/tables.h>
+#include <bits/tcpip.h>
 
 struct io_buffer;
 struct net_device;
 		      struct sockaddr_tcpip *st_dest,
 		      struct net_device *netdev,
 		      uint16_t *trans_csum );
-extern uint16_t tcpip_continue_chksum ( uint16_t partial,
-					const void *data, size_t len );
+extern uint16_t generic_tcpip_continue_chksum ( uint16_t partial,
+						const void *data, size_t len );
 extern uint16_t tcpip_chksum ( const void *data, size_t len );
 
+/* Use generic_tcpip_continue_chksum() if no architecture-specific
+ * version is available
+ */
+#ifndef tcpip_continue_chksum
+#define tcpip_continue_chksum generic_tcpip_continue_chksum
+#endif
+
 #endif /* _IPXE_TCPIP_H */

src/net/tcpip.c

  * or both.  Deciding which to swap is left as an exercise for the
  * interested reader.
  */
-uint16_t tcpip_continue_chksum ( uint16_t partial, const void *data,
-				 size_t len ) {
+uint16_t generic_tcpip_continue_chksum ( uint16_t partial,
+					 const void *data, size_t len ) {
 	unsigned int cksum = ( ( ~partial ) & 0xffff );
 	unsigned int value;
 	unsigned int i;