barrier.h

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#ifndef _ASM_UM_BARRIER_H_
#define _ASM_UM_BARRIER_H_

#include <asm/asm.h>
#include <asm/segment.h>
#include <asm/cpufeature.h>
#include <asm/cmpxchg.h>
#include <asm/nops.h>

#include <linux/kernel.h>
#include <linux/irqflags.h>

/*
 * Force strict CPU ordering.
 * And yes, this is required on UP too when we're talking
 * to devices.
 */
#ifdef CONFIG_X86_32

#define mb()    alternative("lock; addl $0,0(%%esp)", "mfence", X86_FEATURE_XMM2)
#define rmb()   alternative("lock; addl $0,0(%%esp)", "lfence", X86_FEATURE_XMM2)
#define wmb()   alternative("lock; addl $0,0(%%esp)", "sfence", X86_FEATURE_XMM)

#else /* CONFIG_X86_32 */

#define mb()    asm volatile("mfence" : : : "memory")
#define rmb()   asm volatile("lfence" : : : "memory")
#define wmb()   asm volatile("sfence" : : : "memory")

#endif /* CONFIG_X86_32 */

#define read_barrier_depends()  do { } while (0)

#ifdef CONFIG_SMP

#define smp_mb()    mb()
#ifdef CONFIG_X86_PPRO_FENCE
#define smp_rmb()   rmb()
#else /* CONFIG_X86_PPRO_FENCE */
#define smp_rmb()   barrier()
#endif /* CONFIG_X86_PPRO_FENCE */

#ifdef CONFIG_X86_OOSTORE
#define smp_wmb()   wmb()
#else /* CONFIG_X86_OOSTORE */
#define smp_wmb()   barrier()
#endif /* CONFIG_X86_OOSTORE */

#define smp_read_barrier_depends()  read_barrier_depends()
#define set_mb(var, value) do { (void)xchg(&var, value); } while (0)

#else /* CONFIG_SMP */

#define smp_mb()    barrier()
#define smp_rmb()   barrier()
#define smp_wmb()   barrier()
#define smp_read_barrier_depends()  do { } while (0)
#define set_mb(var, value) do { var = value; barrier(); } while (0)

#endif /* CONFIG_SMP */

/*
 * Stop RDTSC speculation. This is needed when you need to use RDTSC
 * (or get_cycles or vread that possibly accesses the TSC) in a defined
 * code region.
 *
 * (Could use an alternative three way for this if there was one.)
 */
static inline void rdtsc_barrier(void)
{
    alternative(ASM_NOP3, "mfence", X86_FEATURE_MFENCE_RDTSC);
    alternative(ASM_NOP3, "lfence", X86_FEATURE_LFENCE_RDTSC);
}

#endif