aboutsummaryrefslogtreecommitdiff
path: root/include/asm-generic/qrwlock.h
blob: 36254d2da8e0e6211d22a4e027cce10d2b96be62 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
/*
 * Queue read/write lock
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
 *
 * Authors: Waiman Long <waiman.long@hp.com>
 */
#ifndef __ASM_GENERIC_QRWLOCK_H
#define __ASM_GENERIC_QRWLOCK_H

#include <linux/atomic.h>
#include <asm/barrier.h>
#include <asm/processor.h>

#include <asm-generic/qrwlock_types.h>

/*
 * Writer states & reader shift and bias.
 */
#define	_QW_WAITING	0x100		/* A writer is waiting	   */
#define	_QW_LOCKED	0x0ff		/* A writer holds the lock */
#define	_QW_WMASK	0x1ff		/* Writer mask		   */
#define	_QR_SHIFT	9		/* Reader count shift	   */
#define _QR_BIAS	(1U << _QR_SHIFT)

/*
 * External function declarations
 */
extern void queued_read_lock_slowpath(struct qrwlock *lock);
extern void queued_write_lock_slowpath(struct qrwlock *lock);

/**
 * queued_read_trylock - try to acquire read lock of a queue rwlock
 * @lock : Pointer to queue rwlock structure
 * Return: 1 if lock acquired, 0 if failed
 */
static inline int queued_read_trylock(struct qrwlock *lock)
{
	u32 cnts;

	cnts = atomic_read(&lock->cnts);
	if (likely(!(cnts & _QW_WMASK))) {
		cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
		if (likely(!(cnts & _QW_WMASK)))
			return 1;
		atomic_sub(_QR_BIAS, &lock->cnts);
	}
	return 0;
}

/**
 * queued_write_trylock - try to acquire write lock of a queue rwlock
 * @lock : Pointer to queue rwlock structure
 * Return: 1 if lock acquired, 0 if failed
 */
static inline int queued_write_trylock(struct qrwlock *lock)
{
	u32 cnts;

	cnts = atomic_read(&lock->cnts);
	if (unlikely(cnts))
		return 0;

	return likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts,
				_QW_LOCKED));
}
/**
 * queued_read_lock - acquire read lock of a queue rwlock
 * @lock: Pointer to queue rwlock structure
 */
static inline void queued_read_lock(struct qrwlock *lock)
{
	u32 cnts;

	cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
	if (likely(!(cnts & _QW_WMASK)))
		return;

	/* The slowpath will decrement the reader count, if necessary. */
	queued_read_lock_slowpath(lock);
}

/**
 * queued_write_lock - acquire write lock of a queue rwlock
 * @lock : Pointer to queue rwlock structure
 */
static inline void queued_write_lock(struct qrwlock *lock)
{
	u32 cnts = 0;
	/* Optimize for the unfair lock case where the fair flag is 0. */
	if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED)))
		return;

	queued_write_lock_slowpath(lock);
}

/**
 * queued_read_unlock - release read lock of a queue rwlock
 * @lock : Pointer to queue rwlock structure
 */
static inline void queued_read_unlock(struct qrwlock *lock)
{
	/*
	 * Atomically decrement the reader count
	 */
	(void)atomic_sub_return_release(_QR_BIAS, &lock->cnts);
}

/**
 * queued_write_unlock - release write lock of a queue rwlock
 * @lock : Pointer to queue rwlock structure
 */
static inline void queued_write_unlock(struct qrwlock *lock)
{
	smp_store_release(&lock->wlocked, 0);
}

/*
 * Remapping rwlock architecture specific functions to the corresponding
 * queue rwlock functions.
 */
#define arch_read_lock(l)	queued_read_lock(l)
#define arch_write_lock(l)	queued_write_lock(l)
#define arch_read_trylock(l)	queued_read_trylock(l)
#define arch_write_trylock(l)	queued_write_trylock(l)
#define arch_read_unlock(l)	queued_read_unlock(l)
#define arch_write_unlock(l)	queued_write_unlock(l)

#endif /* __ASM_GENERIC_QRWLOCK_H */