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 #define read_barrier_depends()  do { } while(0)
  42
  43 #ifdef CONFIG_SMP
  44 # define smp_mb()       mb()
  45 # define smp_rmb()      rmb()
  46 # define smp_wmb()      wmb()
  47 # define smp_read_barrier_depends()     read_barrier_depends()
  48 #else
  49 # define smp_mb()       barrier()
  50 # define smp_rmb()      barrier()
  51 # define smp_wmb()      barrier()
  52 # define smp_read_barrier_depends()     do { } while(0)
  53 #endif
  54
  55 /*
  56  * XXX check on this ---I suspect what Linus really wants here is
  57  * acquire vs release semantics but we can't discuss this stuff with
  58  * Linus just yet.  Grrr...
  59  */
  60 #define set_mb(var, value)      do { (var) = (value); mb(); } while (0)
  61
  62 /*
  63  * The group barrier in front of the rsm & ssm are necessary to ensure
  64  * that none of the previous instructions in the same group are
  65  * affected by the rsm/ssm.
  66  */
  67
  68 #endif /* _ASM_IA64_BARRIER_H */