Merge branch 'dmi-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jdelvar...

[cascardo/linux.git] / include / linux / compiler.h

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 4dac103..00b042c 100644 (file)
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -299,6 +299,23 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
        __u.__val;                                      \
 })
 
+/**
+ * smp_cond_acquire() - Spin wait for cond with ACQUIRE ordering
+ * @cond: boolean expression to wait for
+ *
+ * Equivalent to using smp_load_acquire() on the condition variable but employs
+ * the control dependency of the wait to reduce the barrier on many platforms.
+ *
+ * The control dependency provides a LOAD->STORE order, the additional RMB
+ * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,
+ * aka. ACQUIRE.
+ */
+#define smp_cond_acquire(cond) do {            \
+       while (!(cond))                         \
+               cpu_relax();                    \
+       smp_rmb(); /* ctrl + rmb := acquire */  \
+} while (0)
+
 #endif /* __KERNEL__ */
 
 #endif /* __ASSEMBLY__ */