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kernel/linux-imx6_3.14.28/include/asm-generic/mutex-dec.h 2.7 KB
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  /*
   * include/asm-generic/mutex-dec.h
   *
   * Generic implementation of the mutex fastpath, based on atomic
   * decrement/increment.
   */
  #ifndef _ASM_GENERIC_MUTEX_DEC_H
  #define _ASM_GENERIC_MUTEX_DEC_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
   *  @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 MUST leave the value lower than
   * 1 even when the "1" assertion wasn't true.
   */
  static inline void
  __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
  {
  	if (unlikely(atomic_dec_return(count) < 0))
  		fail_fn(count);
  }
  
  /**
   *  __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
   *
   * Change the count from 1 to a value lower than 1. This function returns 0
   * if the fastpath succeeds, or -1 otherwise.
   */
  static inline int
  __mutex_fastpath_lock_retval(atomic_t *count)
  {
  	if (unlikely(atomic_dec_return(count) < 0))
  		return -1;
  	return 0;
  }
  
  /**
   *  __mutex_fastpath_unlock - try to promote the count 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 count 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, then the
   * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs
   * to return 0 otherwise.
   */
  static inline void
  __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
  {
  	if (unlikely(atomic_inc_return(count) <= 0))
  		fail_fn(count);
  }
  
  #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.
   *
   * If the architecture has no effective trylock variant, it should call the
   * <fail_fn> spinlock-based trylock variant unconditionally.
   */
  static inline int
  __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
  {
  	if (likely(atomic_cmpxchg(count, 1, 0) == 1))
  		return 1;
  	return 0;
  }
  
  #endif