Replace incorrect matching constraint that caused the error with an alternative
that still has the required constraints on the inline assembly.

This is the error message reported by clang:
arch/mips/include/asm/checksum.h:285:27: error: unsupported inline asm: input with type '__be32' (aka 'unsigned int') matching output with type 'unsigned short'
          "0" (htonl(len)), "1" (htonl(proto)), "r" (sum));
                                 ^~~~~~~~~~~~

The changed code can be compiled successfully by both gcc and clang.

Signed-off-by: Daniel Sanders <redacted>
Signed-off-by: Toma Tabacu <redacted>
Suggested-by: Maciej W. Rozycki <redacted>
Cc: Ralf Baechle <redacted>
Cc: Markos Chandras <redacted>
Cc: Leonid Yegoshin <redacted>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
---
v2 replaced the patch following Maciej's suggestion where he observed that
the assembly was somewhat strange and suggested correcting the
constraints and using a local of matching type.

v3 fixed a small whitespace issue.

v4 refreshes the patch.

 arch/mips/include/asm/checksum.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/mips/include/asm/checksum.h b/arch/mips/include/asm/checksum.h
index 5c585c5..3ceacde 100644
--- a/arch/mips/include/asm/checksum.h
+++ b/arch/mips/include/asm/checksum.h

@@ -218,6 +218,8 @@ static __inline__ __sum16 csum_ipv6_magic(const struct in6_addr *saddr,
 					  __u32 len, unsigned short proto,
 					  __wsum sum)
 {
+	__wsum tmp;
+
 	__asm__(
 	"	.set	push		# csum_ipv6_magic\n"
 	"	.set	noreorder	\n"

@@ -270,9 +272,9 @@ static __inline__ __sum16 csum_ipv6_magic(const struct in6_addr *saddr,
 
 	"	addu	%0, $1		# Add final carry\n"
 	"	.set	pop"
-	: "=r" (sum), "=r" (proto)
+	: "=&r" (sum), "=&r" (tmp)
 	: "r" (saddr), "r" (daddr),
-	  "0" (htonl(len)), "1" (htonl(proto)), "r" (sum));
+	  "0" (htonl(len)), "r" (htonl(proto)), "r" (sum));
 
 	return csum_fold(sum);
 }

-- 
2.1.4