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Linux kernel mirror (for testing)
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linux
1/*
2 * include/asm-xtensa/rwsem.h
3 *
4 * This file is subject to the terms and conditions of the GNU General Public
5 * License. See the file "COPYING" in the main directory of this archive
6 * for more details.
7 *
8 * Largely copied from include/asm-ppc/rwsem.h
9 *
10 * Copyright (C) 2001 - 2005 Tensilica Inc.
11 */
12
13#ifndef _XTENSA_RWSEM_H
14#define _XTENSA_RWSEM_H
15
16#ifndef _LINUX_RWSEM_H
17#error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
18#endif
19
20#include <linux/list.h>
21#include <linux/spinlock.h>
22#include <asm/atomic.h>
23#include <asm/system.h>
24
25/*
26 * the semaphore definition
27 */
28struct rw_semaphore {
29 signed long count;
30#define RWSEM_UNLOCKED_VALUE 0x00000000
31#define RWSEM_ACTIVE_BIAS 0x00000001
32#define RWSEM_ACTIVE_MASK 0x0000ffff
33#define RWSEM_WAITING_BIAS (-0x00010000)
34#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
35#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
36 spinlock_t wait_lock;
37 struct list_head wait_list;
38};
39
40#define __RWSEM_INITIALIZER(name) \
41 { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
42 LIST_HEAD_INIT((name).wait_list) }
43
44#define DECLARE_RWSEM(name) \
45 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
46
47extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
48extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
49extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
50extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
51
52static inline void init_rwsem(struct rw_semaphore *sem)
53{
54 sem->count = RWSEM_UNLOCKED_VALUE;
55 spin_lock_init(&sem->wait_lock);
56 INIT_LIST_HEAD(&sem->wait_list);
57}
58
59/*
60 * lock for reading
61 */
62static inline void __down_read(struct rw_semaphore *sem)
63{
64 if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0)
65 smp_wmb();
66 else
67 rwsem_down_read_failed(sem);
68}
69
70static inline int __down_read_trylock(struct rw_semaphore *sem)
71{
72 int tmp;
73
74 while ((tmp = sem->count) >= 0) {
75 if (tmp == cmpxchg(&sem->count, tmp,
76 tmp + RWSEM_ACTIVE_READ_BIAS)) {
77 smp_wmb();
78 return 1;
79 }
80 }
81 return 0;
82}
83
84/*
85 * lock for writing
86 */
87static inline void __down_write(struct rw_semaphore *sem)
88{
89 int tmp;
90
91 tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
92 (atomic_t *)(&sem->count));
93 if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
94 smp_wmb();
95 else
96 rwsem_down_write_failed(sem);
97}
98
99static inline int __down_write_trylock(struct rw_semaphore *sem)
100{
101 int tmp;
102
103 tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
104 RWSEM_ACTIVE_WRITE_BIAS);
105 smp_wmb();
106 return tmp == RWSEM_UNLOCKED_VALUE;
107}
108
109/*
110 * unlock after reading
111 */
112static inline void __up_read(struct rw_semaphore *sem)
113{
114 int tmp;
115
116 smp_wmb();
117 tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
118 if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
119 rwsem_wake(sem);
120}
121
122/*
123 * unlock after writing
124 */
125static inline void __up_write(struct rw_semaphore *sem)
126{
127 smp_wmb();
128 if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
129 (atomic_t *)(&sem->count)) < 0)
130 rwsem_wake(sem);
131}
132
133/*
134 * implement atomic add functionality
135 */
136static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
137{
138 atomic_add(delta, (atomic_t *)(&sem->count));
139}
140
141/*
142 * downgrade write lock to read lock
143 */
144static inline void __downgrade_write(struct rw_semaphore *sem)
145{
146 int tmp;
147
148 smp_wmb();
149 tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
150 if (tmp < 0)
151 rwsem_downgrade_wake(sem);
152}
153
154/*
155 * implement exchange and add functionality
156 */
157static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
158{
159 smp_mb();
160 return atomic_add_return(delta, (atomic_t *)(&sem->count));
161}
162
163static inline int rwsem_is_locked(struct rw_semaphore *sem)
164{
165 return (sem->count != 0);
166}
167
168#endif /* _XTENSA_RWSEM_H */