[PATCH] ARM SMP: Use exclusive load/store for __xchg

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

include/asm-arm/system.h

@@ -323,12 +323,8 @@ do {									\
  * NOTE that this solution won't work on an SMP system, so explcitly
  * forbid it here.
  */
-#ifdef CONFIG_SMP
-#error SMP is not supported on SA1100/SA110
-#else
 #define swp_is_buggy
 #endif
-#endif
 
 static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size)
 {
@@ -337,35 +333,68 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
 #ifdef swp_is_buggy
 	unsigned long flags;
 #endif
+#if __LINUX_ARM_ARCH__ >= 6
+	unsigned int tmp;
+#endif
 
 	switch (size) {
-#ifdef swp_is_buggy
-		case 1:
-			local_irq_save(flags);
-			ret = *(volatile unsigned char *)ptr;
-			*(volatile unsigned char *)ptr = x;
-			local_irq_restore(flags);
-			break;
-
-		case 4:
-			local_irq_save(flags);
-			ret = *(volatile unsigned long *)ptr;
-			*(volatile unsigned long *)ptr = x;
-			local_irq_restore(flags);
-			break;
+#if __LINUX_ARM_ARCH__ >= 6
+	case 1:
+		asm volatile("@	__xchg1\n"
+		"1:	ldrexb	%0, [%3]\n"
+		"	strexb	%1, %2, [%3]\n"
+		"	teq	%1, #0\n"
+		"	bne	1b"
+			: "=&r" (ret), "=&r" (tmp)
+			: "r" (x), "r" (ptr)
+			: "memory", "cc");
+		break;
+	case 4:
+		asm volatile("@	__xchg4\n"
+		"1:	ldrex	%0, [%3]\n"
+		"	strex	%1, %2, [%3]\n"
+		"	teq	%1, #0\n"
+		"	bne	1b"
+			: "=&r" (ret), "=&r" (tmp)
+			: "r" (x), "r" (ptr)
+			: "memory", "cc");
+		break;
+#elif defined(swp_is_buggy)
+#ifdef CONFIG_SMP
+#error SMP is not supported on this platform
+#endif
+	case 1:
+		local_irq_save(flags);
+		ret = *(volatile unsigned char *)ptr;
+		*(volatile unsigned char *)ptr = x;
+		local_irq_restore(flags);
+		break;
+
+	case 4:
+		local_irq_save(flags);
+		ret = *(volatile unsigned long *)ptr;
+		*(volatile unsigned long *)ptr = x;
+		local_irq_restore(flags);
+		break;
 #else
-		case 1:	__asm__ __volatile__ ("swpb %0, %1, [%2]"
-					: "=&r" (ret)
-					: "r" (x), "r" (ptr)
-					: "memory", "cc");
-			break;
-		case 4:	__asm__ __volatile__ ("swp %0, %1, [%2]"
-					: "=&r" (ret)
-					: "r" (x), "r" (ptr)
-					: "memory", "cc");
-			break;
+	case 1:
+		asm volatile("@	__xchg1\n"
+		"	swpb	%0, %1, [%2]"
+			: "=&r" (ret)
+			: "r" (x), "r" (ptr)
+			: "memory", "cc");
+		break;
+	case 4:
+		asm volatile("@	__xchg4\n"
+		"	swp	%0, %1, [%2]"
+			: "=&r" (ret)
+			: "r" (x), "r" (ptr)
+			: "memory", "cc");
+		break;
 #endif
-		default: __bad_xchg(ptr, size), ret = 0;
+	default:
+		__bad_xchg(ptr, size), ret = 0;
+		break;
 	}
 
 	return ret;