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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#include <linux/list.h>
17#include <linux/spinlock.h>
18#include <asm/atomic.h>
19#include <asm/system.h>
20
21/*
22 * the semaphore definition
23 */
24struct rw_semaphore {
25 signed long count;
26#define RWSEM_UNLOCKED_VALUE 0x00000000
27#define RWSEM_ACTIVE_BIAS 0x00000001
28#define RWSEM_ACTIVE_MASK 0x0000ffff
29#define RWSEM_WAITING_BIAS (-0x00010000)
30#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
31#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
32 spinlock_t wait_lock;
33 struct list_head wait_list;
34#if RWSEM_DEBUG
35 int debug;
36#endif
37};
38
39/*
40 * initialisation
41 */
42#if RWSEM_DEBUG
43#define __RWSEM_DEBUG_INIT , 0
44#else
45#define __RWSEM_DEBUG_INIT /* */
46#endif
47
48#define __RWSEM_INITIALIZER(name) \
49 { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
50 LIST_HEAD_INIT((name).wait_list) \
51 __RWSEM_DEBUG_INIT }
52
53#define DECLARE_RWSEM(name) \
54 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
55
56extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
57extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
58extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
59extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
60
61static inline void init_rwsem(struct rw_semaphore *sem)
62{
63 sem->count = RWSEM_UNLOCKED_VALUE;
64 spin_lock_init(&sem->wait_lock);
65 INIT_LIST_HEAD(&sem->wait_list);
66#if RWSEM_DEBUG
67 sem->debug = 0;
68#endif
69}
70
71/*
72 * lock for reading
73 */
74static inline void __down_read(struct rw_semaphore *sem)
75{
76 if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0)
77 smp_wmb();
78 else
79 rwsem_down_read_failed(sem);
80}
81
82static inline int __down_read_trylock(struct rw_semaphore *sem)
83{
84 int tmp;
85
86 while ((tmp = sem->count) >= 0) {
87 if (tmp == cmpxchg(&sem->count, tmp,
88 tmp + RWSEM_ACTIVE_READ_BIAS)) {
89 smp_wmb();
90 return 1;
91 }
92 }
93 return 0;
94}
95
96/*
97 * lock for writing
98 */
99static inline void __down_write(struct rw_semaphore *sem)
100{
101 int tmp;
102
103 tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
104 (atomic_t *)(&sem->count));
105 if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
106 smp_wmb();
107 else
108 rwsem_down_write_failed(sem);
109}
110
111static inline int __down_write_trylock(struct rw_semaphore *sem)
112{
113 int tmp;
114
115 tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
116 RWSEM_ACTIVE_WRITE_BIAS);
117 smp_wmb();
118 return tmp == RWSEM_UNLOCKED_VALUE;
119}
120
121/*
122 * unlock after reading
123 */
124static inline void __up_read(struct rw_semaphore *sem)
125{
126 int tmp;
127
128 smp_wmb();
129 tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
130 if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
131 rwsem_wake(sem);
132}
133
134/*
135 * unlock after writing
136 */
137static inline void __up_write(struct rw_semaphore *sem)
138{
139 smp_wmb();
140 if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
141 (atomic_t *)(&sem->count)) < 0)
142 rwsem_wake(sem);
143}
144
145/*
146 * implement atomic add functionality
147 */
148static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
149{
150 atomic_add(delta, (atomic_t *)(&sem->count));
151}
152
153/*
154 * downgrade write lock to read lock
155 */
156static inline void __downgrade_write(struct rw_semaphore *sem)
157{
158 int tmp;
159
160 smp_wmb();
161 tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
162 if (tmp < 0)
163 rwsem_downgrade_wake(sem);
164}
165
166/*
167 * implement exchange and add functionality
168 */
169static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
170{
171 smp_mb();
172 return atomic_add_return(delta, (atomic_t *)(&sem->count));
173}
174
175#endif /* _XTENSA_RWSEM_XADD_H */