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Merge branch 'linux-4.4' of https://github.com/skeggsb/linux into drm-fixes
[karo-tx-linux.git] / include / linux / osq_lock.h
1 #ifndef __LINUX_OSQ_LOCK_H
2 #define __LINUX_OSQ_LOCK_H
3
4 /*
5  * An MCS like lock especially tailored for optimistic spinning for sleeping
6  * lock implementations (mutex, rwsem, etc).
7  */
8 struct optimistic_spin_node {
9         struct optimistic_spin_node *next, *prev;
10         int locked; /* 1 if lock acquired */
11         int cpu; /* encoded CPU # + 1 value */
12 };
13
14 struct optimistic_spin_queue {
15         /*
16          * Stores an encoded value of the CPU # of the tail node in the queue.
17          * If the queue is empty, then it's set to OSQ_UNLOCKED_VAL.
18          */
19         atomic_t tail;
20 };
21
22 #define OSQ_UNLOCKED_VAL (0)
23
24 /* Init macro and function. */
25 #define OSQ_LOCK_UNLOCKED { ATOMIC_INIT(OSQ_UNLOCKED_VAL) }
26
27 static inline void osq_lock_init(struct optimistic_spin_queue *lock)
28 {
29         atomic_set(&lock->tail, OSQ_UNLOCKED_VAL);
30 }
31
32 extern bool osq_lock(struct optimistic_spin_queue *lock);
33 extern void osq_unlock(struct optimistic_spin_queue *lock);
34
35 static inline bool osq_is_locked(struct optimistic_spin_queue *lock)
36 {
37         return atomic_read(&lock->tail) != OSQ_UNLOCKED_VAL;
38 }
39
40 #endif