include/asm-mips/barrier.h

   1 /*
   2  * This file is subject to the terms and conditions of the GNU General Public
   3  * License.  See the file "COPYING" in the main directory of this archive
   4  * for more details.
   5  *
   6  * Copyright (C) 2006 by Ralf Baechle (ralf@linux-mips.org)
   7  */
   8 #ifndef __ASM_BARRIER_H
   9 #define __ASM_BARRIER_H
  10
  11 /*
  12  * read_barrier_depends - Flush all pending reads that subsequents reads
  13  * depend on.
  14  *
  15  * No data-dependent reads from memory-like regions are ever reordered
  16  * over this barrier.  All reads preceding this primitive are guaranteed
  17  * to access memory (but not necessarily other CPUs' caches) before any
  18  * reads following this primitive that depend on the data return by
  19  * any of the preceding reads.  This primitive is much lighter weight than
  20  * rmb() on most CPUs, and is never heavier weight than is
  21  * rmb().
  22  *
  23  * These ordering constraints are respected by both the local CPU
  24  * and the compiler.
  25  *
  26  * Ordering is not guaranteed by anything other than these primitives,
  27  * not even by data dependencies.  See the documentation for
  28  * memory_barrier() for examples and URLs to more information.
  29  *
  30  * For example, the following code would force ordering (the initial
  31  * value of "a" is zero, "b" is one, and "p" is "&a"):
  32  *
  33  * <programlisting>
  34  *      CPU 0                           CPU 1
  35  *
  36  *      b = 2;
  37  *      memory_barrier();
  38  *      p = &b;                         q = p;
  39  *                                      read_barrier_depends();
  40  *                                      d = *q;
  41  * </programlisting>
  42  *
  43  * because the read of "*q" depends on the read of "p" and these
  44  * two reads are separated by a read_barrier_depends().  However,
  45  * the following code, with the same initial values for "a" and "b":
  46  *
  47  * <programlisting>
  48  *      CPU 0                           CPU 1
  49  *
  50  *      a = 2;
  51  *      memory_barrier();
  52  *      b = 3;                          y = b;
  53  *                                      read_barrier_depends();
  54  *                                      x = a;
  55  * </programlisting>
  56  *
  57  * does not enforce ordering, since there is no data dependency between
  58  * the read of "a" and the read of "b".  Therefore, on some CPUs, such
  59  * as Alpha, "y" could be set to 3 and "x" to 0.  Use rmb()
  60  * in cases like this where there are no data dependencies.
  61  */
  62
  63 #define read_barrier_depends()          do { } while(0)
  64 #define smp_read_barrier_depends()      do { } while(0)
  65
  66 #ifdef CONFIG_CPU_HAS_SYNC
  67 #define __sync()                                \
  68         __asm__ __volatile__(                   \
  69                 ".set   push\n\t"               \
  70                 ".set   noreorder\n\t"          \
  71                 ".set   mips2\n\t"              \
  72                 "sync\n\t"                      \
  73                 ".set   pop"                    \
  74                 : /* no output */               \
  75                 : /* no input */                \
  76                 : "memory")
  77 #else
  78 #define __sync()        do { } while(0)
  79 #endif
  80
  81 #define __fast_iob()                            \
  82         __asm__ __volatile__(                   \
  83                 ".set   push\n\t"               \
  84                 ".set   noreorder\n\t"          \
  85                 "lw     $0,%0\n\t"              \
  86                 "nop\n\t"                       \
  87                 ".set   pop"                    \
  88                 : /* no output */               \
  89                 : "m" (*(int *)CKSEG1)          \
  90                 : "memory")
  91
  92 #define fast_wmb()      __sync()
  93 #define fast_rmb()      __sync()
  94 #define fast_mb()       __sync()
  95 #define fast_iob()                              \
  96         do {                                    \
  97                 __sync();                       \
  98                 __fast_iob();                   \
  99         } while (0)
 100
 101 #ifdef CONFIG_CPU_HAS_WB
 102
 103 #include <asm/wbflush.h>
 104
 105 #define wmb()           fast_wmb()
 106 #define rmb()           fast_rmb()
 107 #define mb()            wbflush()
 108 #define iob()           wbflush()
 109
 110 #else /* !CONFIG_CPU_HAS_WB */
 111
 112 #define wmb()           fast_wmb()
 113 #define rmb()           fast_rmb()
 114 #define mb()            fast_mb()
 115 #define iob()           fast_iob()
 116
 117 #endif /* !CONFIG_CPU_HAS_WB */
 118
 119 #if defined(CONFIG_WEAK_ORDERING) && defined(CONFIG_SMP)
 120 #define __WEAK_ORDERING_MB      "       sync    \n"
 121 #else
 122 #define __WEAK_ORDERING_MB      "               \n"
 123 #endif
 124
 125 #define smp_mb()        __asm__ __volatile__(__WEAK_ORDERING_MB : : :"memory")
 126 #define smp_rmb()       __asm__ __volatile__(__WEAK_ORDERING_MB : : :"memory")
 127 #define smp_wmb()       __asm__ __volatile__(__WEAK_ORDERING_MB : : :"memory")
 128
 129 #define set_mb(var, value) \
 130         do { var = value; smp_mb(); } while (0)
 131
 132 #endif /* __ASM_BARRIER_H */