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  *  @fail_fn: function to call if the original value was not 1
  33  *
  34  * Change the count from 1 to a value lower than 1, and call <fail_fn> if
  35  * it wasn't 1 originally. This function returns 0 if the fastpath succeeds,
  36  * or anything the slow path function returns.
  37  */
  38 static inline int
  39 __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
  40 {
  41         if (unlikely(ia64_fetchadd4_acq(count, -1) != 1))
  42                 return fail_fn(count);
  43         return 0;
  44 }
  45
  46 /**
  47  *  __mutex_fastpath_unlock - try to promote the count from 0 to 1
  48  *  @count: pointer of type atomic_t
  49  *  @fail_fn: function to call if the original value was not 0
  50  *
  51  * Try to promote the count from 0 to 1. If it wasn't 0, call <fail_fn>.
  52  * In the failure case, this function is allowed to either set the value to
  53  * 1, or to set it to a value lower than 1.
  54  *
  55  * If the implementation sets it to a value of lower than 1, then the
  56  * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs
  57  * to return 0 otherwise.
  58  */
  59 static inline void
  60 __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
  61 {
  62         int ret = ia64_fetchadd4_rel(count, 1);
  63         if (unlikely(ret < 0))
  64                 fail_fn(count);
  65 }
  66
  67 #define __mutex_slowpath_needs_to_unlock()              1
  68
  69 /**
  70  * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
  71  *
  72  *  @count: pointer of type atomic_t
  73  *  @fail_fn: fallback function
  74  *
  75  * Change the count from 1 to a value lower than 1, and return 0 (failure)
  76  * if it wasn't 1 originally, or return 1 (success) otherwise. This function
  77  * MUST leave the value lower than 1 even when the "1" assertion wasn't true.
  78  * Additionally, if the value was < 0 originally, this function must not leave
  79  * it to 0 on failure.
  80  *
  81  * If the architecture has no effective trylock variant, it should call the
  82  * <fail_fn> spinlock-based trylock variant unconditionally.
  83  */
  84 static inline int
  85 __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
  86 {
  87         if (cmpxchg_acq(count, 1, 0) == 1)
  88                 return 1;
  89         return 0;
  90 }
  91
  92 #endif