arch/tile: break out the "csum a long" function to <asm/checksum.h>

This makes it available to the tilegx network driver.
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

arch/tile/include/asm/checksum.h

@@ -21,4 +21,22 @@
 __wsum do_csum(const unsigned char *buff, int len);
 #define do_csum do_csum
 
+/*
+ * Return the sum of all the 16-bit subwords in a long.
+ * This sums two subwords on a 32-bit machine, and four on 64 bits.
+ * The implementation does two vector adds to capture any overflow.
+ */
+static inline unsigned int csum_long(unsigned long x)
+{
+	unsigned long ret;
+#ifdef __tilegx__
+	ret = __insn_v2sadu(x, 0);
+	ret = __insn_v2sadu(ret, 0);
+#else
+	ret = __insn_sadh_u(x, 0);
+	ret = __insn_sadh_u(ret, 0);
+#endif
+	return ret;
+}
+
 #endif /* _ASM_TILE_CHECKSUM_H */

arch/tile/lib/checksum.c

@@ -16,19 +16,6 @@
 #include <net/checksum.h>
 #include <linux/module.h>
 
-static inline unsigned int longto16(unsigned long x)
-{
-	unsigned long ret;
-#ifdef __tilegx__
-	ret = __insn_v2sadu(x, 0);
-	ret = __insn_v2sadu(ret, 0);
-#else
-	ret = __insn_sadh_u(x, 0);
-	ret = __insn_sadh_u(ret, 0);
-#endif
-	return ret;
-}
-
 __wsum do_csum(const unsigned char *buff, int len)
 {
 	int odd, count;
@@ -94,7 +81,7 @@ __wsum do_csum(const unsigned char *buff, int len)
 	}
 	if (len & 1)
 		result += *buff;
-	result = longto16(result);
+	result = csum_long(result);
 	if (odd)
 		result = swab16(result);
 out: