x86: add xadd helper macro

Add a common xadd implementation.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h
index efe3ec778a586ff707ba372b0b00c91ad1861a79..0d0d9cdd330986a141dbcc386c3cc4b2e067c2d8 100644 (file)
--- a/arch/x86/include/asm/cmpxchg.h
+++ b/arch/x86/include/asm/cmpxchg.h
@@ -6,6 +6,7 @@
 /* Non-existant functions to indicate usage errors at link time. */
 extern void __xchg_wrong_size(void);
 extern void __cmpxchg_wrong_size(void);
+extern void __xadd_wrong_size(void);
 
 /*
  * Constants for operation sizes. On 32-bit, the 64-bit size it set to
@@ -157,4 +158,46 @@ extern void __cmpxchg_wrong_size(void);
        __cmpxchg_local((ptr), (old), (new), sizeof(*ptr))
 #endif
 
+#define __xadd(ptr, inc, lock)                                         \
+       ({                                                              \
+               __typeof__ (*(ptr)) __ret = (inc);                      \
+               switch (sizeof(*(ptr))) {                               \
+               case __X86_CASE_B:                                      \
+                       asm volatile (lock "xaddb %b0, %1\n"            \
+                                     : "+r" (__ret), "+m" (*(ptr))     \
+                                     : : "memory", "cc");              \
+                       break;                                          \
+               case __X86_CASE_W:                                      \
+                       asm volatile (lock "xaddw %w0, %1\n"            \
+                                     : "+r" (__ret), "+m" (*(ptr))     \
+                                     : : "memory", "cc");              \
+                       break;                                          \
+               case __X86_CASE_L:                                      \
+                       asm volatile (lock "xaddl %0, %1\n"             \
+                                     : "+r" (__ret), "+m" (*(ptr))     \
+                                     : : "memory", "cc");              \
+                       break;                                          \
+               case __X86_CASE_Q:                                      \
+                       asm volatile (lock "xaddq %q0, %1\n"            \
+                                     : "+r" (__ret), "+m" (*(ptr))     \
+                                     : : "memory", "cc");              \
+                       break;                                          \
+               default:                                                \
+                       __xadd_wrong_size();                            \
+               }                                                       \
+               __ret;                                                  \
+       })
+
+/*
+ * xadd() adds "inc" to "*ptr" and atomically returns the previous
+ * value of "*ptr".
+ *
+ * xadd() is locked when multiple CPUs are online
+ * xadd_sync() is always locked
+ * xadd_local() is never locked
+ */
+#define xadd(ptr, inc)         __xadd((ptr), (inc), LOCK_PREFIX)
+#define xadd_sync(ptr, inc)    __xadd((ptr), (inc), "lock; ")
+#define xadd_local(ptr, inc)   __xadd((ptr), (inc), "")
+
 #endif /* ASM_X86_CMPXCHG_H */