arch/powerpc/include/asm/barrier.h

   1 /*
   2  * Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu>
   3  */
   4 #ifndef _ASM_POWERPC_BARRIER_H
   5 #define _ASM_POWERPC_BARRIER_H
   6
   7 /*
   8  * Memory barrier.
   9  * The sync instruction guarantees that all memory accesses initiated
  10  * by this processor have been performed (with respect to all other
  11  * mechanisms that access memory).  The eieio instruction is a barrier
  12  * providing an ordering (separately) for (a) cacheable stores and (b)
  13  * loads and stores to non-cacheable memory (e.g. I/O devices).
  14  *
  15  * mb() prevents loads and stores being reordered across this point.
  16  * rmb() prevents loads being reordered across this point.
  17  * wmb() prevents stores being reordered across this point.
  18  * read_barrier_depends() prevents data-dependent loads being reordered
  19  *      across this point (nop on PPC).
  20  *
  21  * *mb() variants without smp_ prefix must order all types of memory
  22  * operations with one another. sync is the only instruction sufficient
  23  * to do this.
  24  *
  25  * For the smp_ barriers, ordering is for cacheable memory operations
  26  * only. We have to use the sync instruction for smp_mb(), since lwsync
  27  * doesn't order loads with respect to previous stores.  Lwsync can be
  28  * used for smp_rmb() and smp_wmb().
  29  *
  30  * However, on CPUs that don't support lwsync, lwsync actually maps to a
  31  * heavy-weight sync, so smp_wmb() can be a lighter-weight eieio.
  32  */
  33 #define mb()   __asm__ __volatile__ ("sync" : : : "memory")
  34 #define rmb()  __asm__ __volatile__ ("sync" : : : "memory")
  35 #define wmb()  __asm__ __volatile__ ("sync" : : : "memory")
  36 #define read_barrier_depends()  do { } while(0)
  37
  38 #define set_mb(var, value)      do { var = value; mb(); } while (0)
  39
  40 #ifdef CONFIG_SMP
  41
  42 #ifdef __SUBARCH_HAS_LWSYNC
  43 #    define SMPWMB      LWSYNC
  44 #else
  45 #    define SMPWMB      eieio
  46 #endif
  47
  48 #define __lwsync()      __asm__ __volatile__ (stringify_in_c(LWSYNC) : : :"memory")
  49
  50 #define smp_mb()        mb()
  51 #define smp_rmb()       __lwsync()
  52 #define smp_wmb()       __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
  53 #define smp_read_barrier_depends()      read_barrier_depends()
  54 #else
  55 #define __lwsync()      barrier()
  56
  57 #define smp_mb()        barrier()
  58 #define smp_rmb()       barrier()
  59 #define smp_wmb()       barrier()
  60 #define smp_read_barrier_depends()      do { } while(0)
  61 #endif /* CONFIG_SMP */
  62
  63 /*
  64  * This is a barrier which prevents following instructions from being
  65  * started until the value of the argument x is known.  For example, if
  66  * x is a variable loaded from memory, this prevents following
  67  * instructions from being executed until the load has been performed.
  68  */
  69 #define data_barrier(x) \
  70         asm volatile("twi 0,%0,0; isync" : : "r" (x) : "memory");
  71
  72 #define smp_store_release(p, v)                                         \
  73 do {                                                                    \
  74         compiletime_assert_atomic_type(*p);                             \
  75         __lwsync();                                                     \
  76         ACCESS_ONCE(*p) = (v);                                          \
  77 } while (0)
  78
  79 #define smp_load_acquire(p)                                             \
  80 ({                                                                      \
  81         typeof(*p) ___p1 = ACCESS_ONCE(*p);                             \
  82         compiletime_assert_atomic_type(*p);                             \
  83         __lwsync();                                                     \
  84         ___p1;                                                          \
  85 })
  86
  87 #endif /* _ASM_POWERPC_BARRIER_H */