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1/* SPDX-License-Identifier: GPL-2.0-or-later */
2/*
3 * Queue read/write lock
4 *
5 * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
6 *
7 * Authors: Waiman Long <waiman.long@hp.com>
8 */
9#ifndef __ASM_GENERIC_QRWLOCK_H
10#define __ASM_GENERIC_QRWLOCK_H
11
12#include <linux/atomic.h>
13#include <asm/barrier.h>
14#include <asm/processor.h>
15
16#include <asm-generic/qrwlock_types.h>
17
18/*
19 * Writer states & reader shift and bias.
20 */
21#define _QW_WAITING 0x100 /* A writer is waiting */
22#define _QW_LOCKED 0x0ff /* A writer holds the lock */
23#define _QW_WMASK 0x1ff /* Writer mask */
24#define _QR_SHIFT 9 /* Reader count shift */
25#define _QR_BIAS (1U << _QR_SHIFT)
26
27/*
28 * External function declarations
29 */
30extern void queued_read_lock_slowpath(struct qrwlock *lock);
31extern void queued_write_lock_slowpath(struct qrwlock *lock);
32
33/**
34 * queued_read_trylock - try to acquire read lock of a queue rwlock
35 * @lock : Pointer to queue rwlock structure
36 * Return: 1 if lock acquired, 0 if failed
37 */
38static inline int queued_read_trylock(struct qrwlock *lock)
39{
40 u32 cnts;
41
42 cnts = atomic_read(&lock->cnts);
43 if (likely(!(cnts & _QW_WMASK))) {
44 cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
45 if (likely(!(cnts & _QW_WMASK)))
46 return 1;
47 atomic_sub(_QR_BIAS, &lock->cnts);
48 }
49 return 0;
50}
51
52/**
53 * queued_write_trylock - try to acquire write lock of a queue rwlock
54 * @lock : Pointer to queue rwlock structure
55 * Return: 1 if lock acquired, 0 if failed
56 */
57static inline int queued_write_trylock(struct qrwlock *lock)
58{
59 u32 cnts;
60
61 cnts = atomic_read(&lock->cnts);
62 if (unlikely(cnts))
63 return 0;
64
65 return likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts,
66 _QW_LOCKED));
67}
68/**
69 * queued_read_lock - acquire read lock of a queue rwlock
70 * @lock: Pointer to queue rwlock structure
71 */
72static inline void queued_read_lock(struct qrwlock *lock)
73{
74 u32 cnts;
75
76 cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
77 if (likely(!(cnts & _QW_WMASK)))
78 return;
79
80 /* The slowpath will decrement the reader count, if necessary. */
81 queued_read_lock_slowpath(lock);
82}
83
84/**
85 * queued_write_lock - acquire write lock of a queue rwlock
86 * @lock : Pointer to queue rwlock structure
87 */
88static inline void queued_write_lock(struct qrwlock *lock)
89{
90 u32 cnts = 0;
91 /* Optimize for the unfair lock case where the fair flag is 0. */
92 if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED)))
93 return;
94
95 queued_write_lock_slowpath(lock);
96}
97
98/**
99 * queued_read_unlock - release read lock of a queue rwlock
100 * @lock : Pointer to queue rwlock structure
101 */
102static inline void queued_read_unlock(struct qrwlock *lock)
103{
104 /*
105 * Atomically decrement the reader count
106 */
107 (void)atomic_sub_return_release(_QR_BIAS, &lock->cnts);
108}
109
110/**
111 * queued_write_unlock - release write lock of a queue rwlock
112 * @lock : Pointer to queue rwlock structure
113 */
114static inline void queued_write_unlock(struct qrwlock *lock)
115{
116 smp_store_release(&lock->wlocked, 0);
117}
118
119/*
120 * Remapping rwlock architecture specific functions to the corresponding
121 * queue rwlock functions.
122 */
123#define arch_read_lock(l) queued_read_lock(l)
124#define arch_write_lock(l) queued_write_lock(l)
125#define arch_read_trylock(l) queued_read_trylock(l)
126#define arch_write_trylock(l) queued_write_trylock(l)
127#define arch_read_unlock(l) queued_read_unlock(l)
128#define arch_write_unlock(l) queued_write_unlock(l)
129
130#endif /* __ASM_GENERIC_QRWLOCK_H */
1/* SPDX-License-Identifier: GPL-2.0-or-later */
2/*
3 * Queue read/write lock
4 *
5 * These use generic atomic and locking routines, but depend on a fair spinlock
6 * implementation in order to be fair themselves. The implementation in
7 * asm-generic/spinlock.h meets these requirements.
8 *
9 * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
10 *
11 * Authors: Waiman Long <waiman.long@hp.com>
12 */
13#ifndef __ASM_GENERIC_QRWLOCK_H
14#define __ASM_GENERIC_QRWLOCK_H
15
16#include <linux/atomic.h>
17#include <asm/barrier.h>
18#include <asm/processor.h>
19
20#include <asm-generic/qrwlock_types.h>
21
22/* Must be included from asm/spinlock.h after defining arch_spin_is_locked. */
23
24/*
25 * Writer states & reader shift and bias.
26 */
27#define _QW_WAITING 0x100 /* A writer is waiting */
28#define _QW_LOCKED 0x0ff /* A writer holds the lock */
29#define _QW_WMASK 0x1ff /* Writer mask */
30#define _QR_SHIFT 9 /* Reader count shift */
31#define _QR_BIAS (1U << _QR_SHIFT)
32
33/*
34 * External function declarations
35 */
36extern void queued_read_lock_slowpath(struct qrwlock *lock);
37extern void queued_write_lock_slowpath(struct qrwlock *lock);
38
39/**
40 * queued_read_trylock - try to acquire read lock of a queued rwlock
41 * @lock : Pointer to queued rwlock structure
42 * Return: 1 if lock acquired, 0 if failed
43 */
44static inline int queued_read_trylock(struct qrwlock *lock)
45{
46 int cnts;
47
48 cnts = atomic_read(&lock->cnts);
49 if (likely(!(cnts & _QW_WMASK))) {
50 cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
51 if (likely(!(cnts & _QW_WMASK)))
52 return 1;
53 atomic_sub(_QR_BIAS, &lock->cnts);
54 }
55 return 0;
56}
57
58/**
59 * queued_write_trylock - try to acquire write lock of a queued rwlock
60 * @lock : Pointer to queued rwlock structure
61 * Return: 1 if lock acquired, 0 if failed
62 */
63static inline int queued_write_trylock(struct qrwlock *lock)
64{
65 int cnts;
66
67 cnts = atomic_read(&lock->cnts);
68 if (unlikely(cnts))
69 return 0;
70
71 return likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts,
72 _QW_LOCKED));
73}
74/**
75 * queued_read_lock - acquire read lock of a queued rwlock
76 * @lock: Pointer to queued rwlock structure
77 */
78static inline void queued_read_lock(struct qrwlock *lock)
79{
80 int cnts;
81
82 cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
83 if (likely(!(cnts & _QW_WMASK)))
84 return;
85
86 /* The slowpath will decrement the reader count, if necessary. */
87 queued_read_lock_slowpath(lock);
88}
89
90/**
91 * queued_write_lock - acquire write lock of a queued rwlock
92 * @lock : Pointer to queued rwlock structure
93 */
94static inline void queued_write_lock(struct qrwlock *lock)
95{
96 int cnts = 0;
97 /* Optimize for the unfair lock case where the fair flag is 0. */
98 if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED)))
99 return;
100
101 queued_write_lock_slowpath(lock);
102}
103
104/**
105 * queued_read_unlock - release read lock of a queued rwlock
106 * @lock : Pointer to queued rwlock structure
107 */
108static inline void queued_read_unlock(struct qrwlock *lock)
109{
110 /*
111 * Atomically decrement the reader count
112 */
113 (void)atomic_sub_return_release(_QR_BIAS, &lock->cnts);
114}
115
116/**
117 * queued_write_unlock - release write lock of a queued rwlock
118 * @lock : Pointer to queued rwlock structure
119 */
120static inline void queued_write_unlock(struct qrwlock *lock)
121{
122 smp_store_release(&lock->wlocked, 0);
123}
124
125/**
126 * queued_rwlock_is_contended - check if the lock is contended
127 * @lock : Pointer to queued rwlock structure
128 * Return: 1 if lock contended, 0 otherwise
129 */
130static inline int queued_rwlock_is_contended(struct qrwlock *lock)
131{
132 return arch_spin_is_locked(&lock->wait_lock);
133}
134
135/*
136 * Remapping rwlock architecture specific functions to the corresponding
137 * queued rwlock functions.
138 */
139#define arch_read_lock(l) queued_read_lock(l)
140#define arch_write_lock(l) queued_write_lock(l)
141#define arch_read_trylock(l) queued_read_trylock(l)
142#define arch_write_trylock(l) queued_write_trylock(l)
143#define arch_read_unlock(l) queued_read_unlock(l)
144#define arch_write_unlock(l) queued_write_unlock(l)
145#define arch_rwlock_is_contended(l) queued_rwlock_is_contended(l)
146
147#endif /* __ASM_GENERIC_QRWLOCK_H */