/*
   * Assembly implementation of the mutex fastpath, based on atomic
   * decrement/increment.
   *
   * started by Ingo Molnar:
   *
   *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   */

  #ifndef _ASM_X86_MUTEX_32_H
  #define _ASM_X86_MUTEX_32_H

  #include <asm/alternative.h>

  /**
   *  __mutex_fastpath_lock - try to take the lock by moving the count
   *                          from 1 to a 0 value
   *  @count: pointer of type atomic_t
   *  @fn: function to call if the original value was not 1
   *
   * Change the count from 1 to a value lower than 1, and call <fn> if it
   * wasn't 1 originally. This function MUST leave the value lower than 1
   * even when the "1" assertion wasn't true.
   */

  #define __mutex_fastpath_lock(count, fail_fn)			\
  do {								\
  	unsigned int dummy;					\
  								\
  	typecheck(atomic_t *, count);				\

  	typecheck_fn(void (*)(atomic_t *), fail_fn);		\

  								\
  	asm volatile(LOCK_PREFIX "   decl (%%eax)
  "		\
  		     "   jns 1f	
  "				\
  		     "   call " #fail_fn "
  "			\
  		     "1:
  "					\
  		     : "=a" (dummy)				\
  		     : "a" (count)				\
  		     : "memory", "ecx", "edx");			\

  } while (0)
  
  
  /**
   *  __mutex_fastpath_lock_retval - try to take the lock by moving the count
   *                                 from 1 to a 0 value
   *  @count: pointer of type atomic_t
   *  @fail_fn: function to call if the original value was not 1
   *
   * Change the count from 1 to a value lower than 1, and call <fail_fn> if it
   * wasn't 1 originally. This function returns 0 if the fastpath succeeds,
   * or anything the slow path function returns
   */

  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
  		return 0;
  }
  
  /**
   *  __mutex_fastpath_unlock - try to promote the mutex from 0 to 1
   *  @count: pointer of type atomic_t
   *  @fail_fn: function to call if the original value was not 0
   *
   * try to promote the mutex from 0 to 1. if it wasn't 0, call <fail_fn>.
   * In the failure case, this function is allowed to either set the value
   * to 1, or to set it to a value lower than 1.
   *
   * If the implementation sets it to a value of lower than 1, the
   * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs
   * to return 0 otherwise.
   */

  #define __mutex_fastpath_unlock(count, fail_fn)			\
  do {								\
  	unsigned int dummy;					\
  								\
  	typecheck(atomic_t *, count);				\

  	typecheck_fn(void (*)(atomic_t *), fail_fn);		\

  								\
  	asm volatile(LOCK_PREFIX "   incl (%%eax)
  "		\
  		     "   jg	1f
  "				\
  		     "   call " #fail_fn "
  "			\
  		     "1:
  "					\
  		     : "=a" (dummy)				\
  		     : "a" (count)				\
  		     : "memory", "ecx", "edx");			\

  } while (0)
  
  #define __mutex_slowpath_needs_to_unlock()	1
  
  /**
   * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
   *
   *  @count: pointer of type atomic_t
   *  @fail_fn: fallback function
   *
   * Change the count from 1 to a value lower than 1, and return 0 (failure)
   * if it wasn't 1 originally, or return 1 (success) otherwise. This function
   * MUST leave the value lower than 1 even when the "1" assertion wasn't true.
   * Additionally, if the value was < 0 originally, this function must not leave
   * it to 0 on failure.
   */

  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))

  		return 1;
  	return 0;
  #else
  	return fail_fn(count);
  #endif
  }

  #endif /* _ASM_X86_MUTEX_32_H */