x86: Add xadd helper macro

Add a common xadd implementation.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Link: http://lkml.kernel.org/r/4E5BCC40.3030501@goop.org
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h
index efe3ec778a58..0d0d9cdd3309 100644
--- 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 */