1 /*
2  * Queued spinlock
3  *
4  * This program is free software; you can redistribute it and/or modify
5  * it under the terms of the GNU General Public License as published by
6  * the Free Software Foundation; either version 2 of the License, or
7  * (at your option) any later version.
8  *
9  * This program is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  * GNU General Public License for more details.
13  *
14  * (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P.
15  *
16  * Authors: Waiman Long <waiman.long@hp.com>
17  */
18 #ifndef __ASM_GENERIC_QSPINLOCK_H
19 #define __ASM_GENERIC_QSPINLOCK_H
20 
21 #include <asm-generic/qspinlock_types.h>
22 
23 /**
24  * queued_spin_is_locked - is the spinlock locked?
25  * @lock: Pointer to queued spinlock structure
26  * Return: 1 if it is locked, 0 otherwise
27  */
28 static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
29 {
30 	return atomic_read(&lock->val);
31 }
32 
33 /**
34  * queued_spin_value_unlocked - is the spinlock structure unlocked?
35  * @lock: queued spinlock structure
36  * Return: 1 if it is unlocked, 0 otherwise
37  *
38  * N.B. Whenever there are tasks waiting for the lock, it is considered
39  *      locked wrt the lockref code to avoid lock stealing by the lockref
40  *      code and change things underneath the lock. This also allows some
41  *      optimizations to be applied without conflict with lockref.
42  */
43 static __always_inline int queued_spin_value_unlocked(struct qspinlock lock)
44 {
45 	return !atomic_read(&lock.val);
46 }
47 
48 /**
49  * queued_spin_is_contended - check if the lock is contended
50  * @lock : Pointer to queued spinlock structure
51  * Return: 1 if lock contended, 0 otherwise
52  */
53 static __always_inline int queued_spin_is_contended(struct qspinlock *lock)
54 {
55 	return atomic_read(&lock->val) & ~_Q_LOCKED_MASK;
56 }
57 /**
58  * queued_spin_trylock - try to acquire the queued spinlock
59  * @lock : Pointer to queued spinlock structure
60  * Return: 1 if lock acquired, 0 if failed
61  */
62 static __always_inline int queued_spin_trylock(struct qspinlock *lock)
63 {
64 	if (!atomic_read(&lock->val) &&
65 	   (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) == 0))
66 		return 1;
67 	return 0;
68 }
69 
70 extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
71 
72 /**
73  * queued_spin_lock - acquire a queued spinlock
74  * @lock: Pointer to queued spinlock structure
75  */
76 static __always_inline void queued_spin_lock(struct qspinlock *lock)
77 {
78 	u32 val;
79 
80 	val = atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL);
81 	if (likely(val == 0))
82 		return;
83 	queued_spin_lock_slowpath(lock, val);
84 }
85 
86 #ifndef queued_spin_unlock
87 /**
88  * queued_spin_unlock - release a queued spinlock
89  * @lock : Pointer to queued spinlock structure
90  */
91 static __always_inline void queued_spin_unlock(struct qspinlock *lock)
92 {
93 	/*
94 	 * smp_mb__before_atomic() in order to guarantee release semantics
95 	 */
96 	smp_mb__before_atomic_dec();
97 	atomic_sub(_Q_LOCKED_VAL, &lock->val);
98 }
99 #endif
100 
101 /**
102  * queued_spin_unlock_wait - wait until current lock holder releases the lock
103  * @lock : Pointer to queued spinlock structure
104  *
105  * There is a very slight possibility of live-lock if the lockers keep coming
106  * and the waiter is just unfortunate enough to not see any unlock state.
107  */
108 static inline void queued_spin_unlock_wait(struct qspinlock *lock)
109 {
110 	while (atomic_read(&lock->val) & _Q_LOCKED_MASK)
111 		cpu_relax();
112 }
113 
114 #ifndef virt_spin_lock
115 static __always_inline bool virt_spin_lock(struct qspinlock *lock)
116 {
117 	return false;
118 }
119 #endif
120 
121 /*
122  * Initializier
123  */
124 #define	__ARCH_SPIN_LOCK_UNLOCKED	{ ATOMIC_INIT(0) }
125 
126 /*
127  * Remapping spinlock architecture specific functions to the corresponding
128  * queued spinlock functions.
129  */
130 #define arch_spin_is_locked(l)		queued_spin_is_locked(l)
131 #define arch_spin_is_contended(l)	queued_spin_is_contended(l)
132 #define arch_spin_value_unlocked(l)	queued_spin_value_unlocked(l)
133 #define arch_spin_lock(l)		queued_spin_lock(l)
134 #define arch_spin_trylock(l)		queued_spin_trylock(l)
135 #define arch_spin_unlock(l)		queued_spin_unlock(l)
136 #define arch_spin_lock_flags(l, f)	queued_spin_lock(l)
137 #define arch_spin_unlock_wait(l)	queued_spin_unlock_wait(l)
138 
139 #endif /* __ASM_GENERIC_QSPINLOCK_H */
140