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mutex.h

/*
 * Pull in the generic implementation for the mutex fastpath.
 *
 * TODO: implement optimized primitives instead, or leave the generic
 * implementation in place, or pick the atomic_xchg() based generic
 * implementation. (see asm-generic/mutex-xchg.h for details)
 *
 * Copyright 2006-2009 Analog Devices Inc.
 *
 * Licensed under the GPL-2 or later.
 */

#ifndef _ASM_MUTEX_H
#define _ASM_MUTEX_H

#ifndef CONFIG_SMP
#include <asm-generic/mutex.h>
#else

static inline void
__mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
{
      if (unlikely(atomic_dec_return(count) < 0))
            fail_fn(count);
      else
            smp_mb();
}

static inline int
__mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
{
      if (unlikely(atomic_dec_return(count) < 0))
            return fail_fn(count);
      else {
            smp_mb();
            return 0;
      }
}

static inline void
__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
{
      smp_mb();
      if (unlikely(atomic_inc_return(count) <= 0))
            fail_fn(count);
}

#define __mutex_slowpath_needs_to_unlock()            1

static inline int
__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
{
      /*
       * We have two variants here. The cmpxchg based one is the best one
       * because it never induce a false contention state.  It is included
       * here because architectures using the inc/dec algorithms over the
       * xchg ones are much more likely to support cmpxchg natively.
       *
       * If not we fall back to the spinlock based variant - that is
       * just as efficient (and simpler) as a 'destructive' probing of
       * the mutex state would be.
       */
#ifdef __HAVE_ARCH_CMPXCHG
      if (likely(atomic_cmpxchg(count, 1, 0) == 1)) {
            smp_mb();
            return 1;
      }
      return 0;
#else
      return fail_fn(count);
#endif
}

#endif

#endif

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