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