blob: ae782254e731bbcd03c8152379b4adf6ddea01a7 [file] [log] [blame]
* Copyright (C) 1999 Cort Dougan <>
* Memory barrier.
* The sync instruction guarantees that all memory accesses initiated
* by this processor have been performed (with respect to all other
* mechanisms that access memory). The eieio instruction is a barrier
* providing an ordering (separately) for (a) cacheable stores and (b)
* loads and stores to non-cacheable memory (e.g. I/O devices).
* mb() prevents loads and stores being reordered across this point.
* rmb() prevents loads being reordered across this point.
* wmb() prevents stores being reordered across this point.
* read_barrier_depends() prevents data-dependent loads being reordered
* across this point (nop on PPC).
* *mb() variants without smp_ prefix must order all types of memory
* operations with one another. sync is the only instruction sufficient
* to do this.
* For the smp_ barriers, ordering is for cacheable memory operations
* only. We have to use the sync instruction for smp_mb(), since lwsync
* doesn't order loads with respect to previous stores. Lwsync can be
* used for smp_rmb() and smp_wmb().
* However, on CPUs that don't support lwsync, lwsync actually maps to a
* heavy-weight sync, so smp_wmb() can be a lighter-weight eieio.
#define mb() __asm__ __volatile__ ("sync" : : : "memory")
#define rmb() __asm__ __volatile__ ("sync" : : : "memory")
#define wmb() __asm__ __volatile__ ("sync" : : : "memory")
#define read_barrier_depends() do { } while(0)
#define set_mb(var, value) do { var = value; mb(); } while (0)
# define SMPWMB eieio
#define smp_mb() mb()
#define smp_rmb() __asm__ __volatile__ (stringify_in_c(LWSYNC) : : :"memory")
#define smp_wmb() __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
#define smp_read_barrier_depends() read_barrier_depends()
#define smp_mb() barrier()
#define smp_rmb() barrier()
#define smp_wmb() barrier()
#define smp_read_barrier_depends() do { } while(0)
#endif /* CONFIG_SMP */
* This is a barrier which prevents following instructions from being
* started until the value of the argument x is known. For example, if
* x is a variable loaded from memory, this prevents following
* instructions from being executed until the load has been performed.
#define data_barrier(x) \
asm volatile("twi 0,%0,0; isync" : : "r" (x) : "memory");