1. 根目录:
2. arch
3. ia64
4. include
5. asm
6. barrier.h

/*
 * Memory barrier definitions.  This is based on information published
 * in the Processor Abstraction Layer and the System Abstraction Layer
 * manual.
 *
 * Copyright (C) 1998-2003 Hewlett-Packard Co
 *	David Mosberger-Tang <davidm@hpl.hp.com>
 * Copyright (C) 1999 Asit Mallick <asit.k.mallick@intel.com>
 * Copyright (C) 1999 Don Dugger <don.dugger@intel.com>
 */
#ifndef _ASM_IA64_BARRIER_H
#define _ASM_IA64_BARRIER_H

#include <linux/compiler.h>

/*
 * Macros to force memory ordering.  In these descriptions, "previous"
 * and "subsequent" refer to program order; "visible" means that all
 * architecturally visible effects of a memory access have occurred
 * (at a minimum, this means the memory has been read or written).
 *
 *   wmb():	Guarantees that all preceding stores to memory-
 *		like regions are visible before any subsequent
 *		stores and that all following stores will be
 *		visible only after all previous stores.
 *   rmb():	Like wmb(), but for reads.
 *   mb():	wmb()/rmb() combo, i.e., all previous memory
 *		accesses are visible before all subsequent
 *		accesses and vice versa.  This is also known as
 *		a "fence."
 *
 * Note: "mb()" and its variants cannot be used as a fence to order
 * accesses to memory mapped I/O registers.  For that, mf.a needs to
 * be used.  However, we don't want to always use mf.a because (a)
 * it's (presumably) much slower than mf and (b) mf.a is supported for
 * sequential memory pages only.
 */
#define mb()	ia64_mf()
#define rmb()	mb()
#define wmb()	mb()
#define read_barrier_depends()	do { } while(0)

#ifdef CONFIG_SMP
# define smp_mb()	mb()
# define smp_rmb()	rmb()
# define smp_wmb()	wmb()
# define smp_read_barrier_depends()	read_barrier_depends()

#else

# define smp_mb()	barrier()
# define smp_rmb()	barrier()
# define smp_wmb()	barrier()
# define smp_read_barrier_depends()	do { } while(0)

#endif

/*
 * IA64 GCC turns volatile stores into st.rel and volatile loads into ld.acq no
 * need for asm trickery!
 */

#define smp_store_release(p, v)						\
do {									\
	compiletime_assert_atomic_type(*p);				\
	barrier();							\
	ACCESS_ONCE(*p) = (v);						\
} while (0)

#define smp_load_acquire(p)						\
({									\
	typeof(*p) ___p1 = ACCESS_ONCE(*p);				\
	compiletime_assert_atomic_type(*p);				\
	barrier();							\
	___p1;								\
})

/*
 * XXX check on this ---I suspect what Linus really wants here is
 * acquire vs release semantics but we can't discuss this stuff with
 * Linus just yet.  Grrr...
 */
#define set_mb(var, value)	do { (var) = (value); mb(); } while (0)

/*
 * The group barrier in front of the rsm & ssm are necessary to ensure
 * that none of the previous instructions in the same group are
 * affected by the rsm/ssm.
 */

#endif /* _ASM_IA64_BARRIER_H */