[MIPS] MIPS R2 optimized endianess swapping.

From Franck Bui-Huu <vagabon.xyz@gmail.com> with modifications by me.
    
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

include/asm-mips/byteorder.h

@@ -8,10 +8,39 @@
 #ifndef _ASM_BYTEORDER_H
 #define _ASM_BYTEORDER_H
 
+#include <linux/config.h>
+#include <linux/compiler.h>
 #include <asm/types.h>
 
 #ifdef __GNUC__
 
+#ifdef CONFIG_CPU_MIPSR2
+
+static __inline__ __attribute_const__ __u16 ___arch__swab16(__u16 x)
+{
+	__asm__(
+	"	wsbh	%0, %1			\n"
+	: "=r" (x)
+	: "r" (x));
+
+	return x;
+}
+#define __arch__swab16(x)	___arch__swab16(x)
+
+static __inline__ __attribute_const__ __u32 ___arch__swab32(__u32 x)
+{
+	__asm__(
+	"	wsbh	%0, %1			\n"
+	"	rotr	%0, %0, 16		\n"
+	: "=r" (x)
+	: "r" (x));
+
+	return x;
+}
+#define __arch__swab32(x)	___arch__swab32(x)
+
+#endif /* CONFIG_CPU_MIPSR2 */
+
 #if !defined(__STRICT_ANSI__) || defined(__KERNEL__)
 #  define __BYTEORDER_HAS_U64__
 #  define __SWAB_64_THRU_32__