arch/ia64/include/asm/barrier.h

   1 /*
   2  * Memory barrier definitions.  This is based on information published
   3  * in the Processor Abstraction Layer and the System Abstraction Layer
   4  * manual.
   5  *
   6  * Copyright (C) 1998-2003 Hewlett-Packard Co
   7  *      David Mosberger-Tang <davidm@hpl.hp.com>
   8  * Copyright (C) 1999 Asit Mallick <asit.k.mallick@intel.com>
   9  * Copyright (C) 1999 Don Dugger <don.dugger@intel.com>
  10  */
  11 #ifndef _ASM_IA64_BARRIER_H
  12 #define _ASM_IA64_BARRIER_H
  13
  14 #include <linux/compiler.h>
  15
  16 /*
  17  * Macros to force memory ordering.  In these descriptions, "previous"
  18  * and "subsequent" refer to program order; "visible" means that all
  19  * architecturally visible effects of a memory access have occurred
  20  * (at a minimum, this means the memory has been read or written).
  21  *
  22  *   wmb():     Guarantees that all preceding stores to memory-
  23  *              like regions are visible before any subsequent
  24  *              stores and that all following stores will be
  25  *              visible only after all previous stores.
  26  *   rmb():     Like wmb(), but for reads.
  27  *   mb():      wmb()/rmb() combo, i.e., all previous memory
  28  *              accesses are visible before all subsequent
  29  *              accesses and vice versa.  This is also known as
  30  *              a "fence."
  31  *
  32  * Note: "mb()" and its variants cannot be used as a fence to order
  33  * accesses to memory mapped I/O registers.  For that, mf.a needs to
  34  * be used.  However, we don't want to always use mf.a because (a)
  35  * it's (presumably) much slower than mf and (b) mf.a is supported for
  36  * sequential memory pages only.
  37  */
  38 #define mb()            ia64_mf()
  39 #define rmb()           mb()
  40 #define wmb()           mb()
  41
  42 #define dma_rmb()       mb()
  43 #define dma_wmb()       mb()
  44
  45 #ifdef CONFIG_SMP
  46 # define smp_mb()       mb()
  47 #else
  48 # define smp_mb()       barrier()
  49 #endif
  50
  51 #define smp_rmb()       smp_mb()
  52 #define smp_wmb()       smp_mb()
  53
  54 #define read_barrier_depends()          do { } while (0)
  55 #define smp_read_barrier_depends()      do { } while (0)
  56
  57 #define smp_mb__before_atomic() barrier()
  58 #define smp_mb__after_atomic()  barrier()
  59
  60 /*
  61  * IA64 GCC turns volatile stores into st.rel and volatile loads into ld.acq no
  62  * need for asm trickery!
  63  */
  64
  65 #define smp_store_release(p, v)                                         \
  66 do {                                                                    \
  67         compiletime_assert_atomic_type(*p);                             \
  68         barrier();                                                      \
  69         ACCESS_ONCE(*p) = (v);                                          \
  70 } while (0)
  71
  72 #define smp_load_acquire(p)                                             \
  73 ({                                                                      \
  74         typeof(*p) ___p1 = ACCESS_ONCE(*p);                             \
  75         compiletime_assert_atomic_type(*p);                             \
  76         barrier();                                                      \
  77         ___p1;                                                          \
  78 })
  79
  80 /*
  81  * XXX check on this ---I suspect what Linus really wants here is
  82  * acquire vs release semantics but we can't discuss this stuff with
  83  * Linus just yet.  Grrr...
  84  */
  85 #define set_mb(var, value)      do { (var) = (value); mb(); } while (0)
  86
  87 /*
  88  * The group barrier in front of the rsm & ssm are necessary to ensure
  89  * that none of the previous instructions in the same group are
  90  * affected by the rsm/ssm.
  91  */
  92
  93 #endif /* _ASM_IA64_BARRIER_H */