arch/ia64/include/asm/mutex.h

   1 /*
   2  * ia64 implementation of the mutex fastpath.
   3  *
   4  * Copyright (C) 2006 Ken Chen <kenneth.w.chen@intel.com>
   5  *
   6  */
   7
   8 #ifndef _ASM_MUTEX_H
   9 #define _ASM_MUTEX_H
  10
  11 /**
  12  *  __mutex_fastpath_lock - try to take the lock by moving the count
  13  *                          from 1 to a 0 value
  14  *  @count: pointer of type atomic_t
  15  *  @fail_fn: function to call if the original value was not 1
  16  *
  17  * Change the count from 1 to a value lower than 1, and call <fail_fn> if
  18  * it wasn't 1 originally. This function MUST leave the value lower than
  19  * 1 even when the "1" assertion wasn't true.
  20  */
  21 static inline void
  22 __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
  23 {
  24         if (unlikely(ia64_fetchadd4_acq(count, -1) != 1))
  25                 fail_fn(count);
  26 }
  27
  28 /**
  29  *  __mutex_fastpath_lock_retval - try to take the lock by moving the count
  30  *                                 from 1 to a 0 value
  31  *  @count: pointer of type atomic_t
  32  *
  33  * Change the count from 1 to a value lower than 1. This function returns 0
  34  * if the fastpath succeeds, or -1 otherwise.
  35  */
  36 static inline int
  37 __mutex_fastpath_lock_retval(atomic_t *count)
  38 {
  39         if (unlikely(ia64_fetchadd4_acq(count, -1) != 1))
  40                 return -1;
  41         return 0;
  42 }
  43
  44 /**
  45  *  __mutex_fastpath_unlock - try to promote the count from 0 to 1
  46  *  @count: pointer of type atomic_t
  47  *  @fail_fn: function to call if the original value was not 0
  48  *
  49  * Try to promote the count from 0 to 1. If it wasn't 0, call <fail_fn>.
  50  * In the failure case, this function is allowed to either set the value to
  51  * 1, or to set it to a value lower than 1.
  52  *
  53  * If the implementation sets it to a value of lower than 1, then the
  54  * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs
  55  * to return 0 otherwise.
  56  */
  57 static inline void
  58 __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
  59 {
  60         int ret = ia64_fetchadd4_rel(count, 1);
  61         if (unlikely(ret < 0))
  62                 fail_fn(count);
  63 }
  64
  65 #define __mutex_slowpath_needs_to_unlock()              1
  66
  67 /**
  68  * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
  69  *
  70  *  @count: pointer of type atomic_t
  71  *  @fail_fn: fallback function
  72  *
  73  * Change the count from 1 to a value lower than 1, and return 0 (failure)
  74  * if it wasn't 1 originally, or return 1 (success) otherwise. This function
  75  * MUST leave the value lower than 1 even when the "1" assertion wasn't true.
  76  * Additionally, if the value was < 0 originally, this function must not leave
  77  * it to 0 on failure.
  78  *
  79  * If the architecture has no effective trylock variant, it should call the
  80  * <fail_fn> spinlock-based trylock variant unconditionally.
  81  */
  82 static inline int
  83 __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
  84 {
  85         if (cmpxchg_acq(count, 1, 0) == 1)
  86                 return 1;
  87         return 0;
  88 }
  89
  90 #endif