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1#ifndef _ASM_POWERPC_RWSEM_H
2#define _ASM_POWERPC_RWSEM_H
3
4#ifdef __KERNEL__
5
6/*
7 * include/asm-powerpc/rwsem.h: R/W semaphores for PPC using the stuff
8 * in lib/rwsem.c. Adapted largely from include/asm-i386/rwsem.h
9 * by Paul Mackerras <paulus@samba.org>.
10 */
11
12#include <linux/list.h>
13#include <linux/spinlock.h>
14#include <asm/atomic.h>
15#include <asm/system.h>
16
17/*
18 * the semaphore definition
19 */
20struct rw_semaphore {
21 /* XXX this should be able to be an atomic_t -- paulus */
22 signed int count;
23#define RWSEM_UNLOCKED_VALUE 0x00000000
24#define RWSEM_ACTIVE_BIAS 0x00000001
25#define RWSEM_ACTIVE_MASK 0x0000ffff
26#define RWSEM_WAITING_BIAS (-0x00010000)
27#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
28#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
29 spinlock_t wait_lock;
30 struct list_head wait_list;
31};
32
33#define __RWSEM_INITIALIZER(name) \
34 { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
35 LIST_HEAD_INIT((name).wait_list) }
36
37#define DECLARE_RWSEM(name) \
38 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
39
40extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
41extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
42extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
43extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
44
45static inline void init_rwsem(struct rw_semaphore *sem)
46{
47 sem->count = RWSEM_UNLOCKED_VALUE;
48 spin_lock_init(&sem->wait_lock);
49 INIT_LIST_HEAD(&sem->wait_list);
50}
51
52/*
53 * lock for reading
54 */
55static inline void __down_read(struct rw_semaphore *sem)
56{
57 if (unlikely(atomic_inc_return((atomic_t *)(&sem->count)) <= 0))
58 rwsem_down_read_failed(sem);
59}
60
61static inline int __down_read_trylock(struct rw_semaphore *sem)
62{
63 int tmp;
64
65 while ((tmp = sem->count) >= 0) {
66 if (tmp == cmpxchg(&sem->count, tmp,
67 tmp + RWSEM_ACTIVE_READ_BIAS)) {
68 return 1;
69 }
70 }
71 return 0;
72}
73
74/*
75 * lock for writing
76 */
77static inline void __down_write(struct rw_semaphore *sem)
78{
79 int tmp;
80
81 tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
82 (atomic_t *)(&sem->count));
83 if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
84 rwsem_down_write_failed(sem);
85}
86
87static inline int __down_write_trylock(struct rw_semaphore *sem)
88{
89 int tmp;
90
91 tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
92 RWSEM_ACTIVE_WRITE_BIAS);
93 return tmp == RWSEM_UNLOCKED_VALUE;
94}
95
96/*
97 * unlock after reading
98 */
99static inline void __up_read(struct rw_semaphore *sem)
100{
101 int tmp;
102
103 tmp = atomic_dec_return((atomic_t *)(&sem->count));
104 if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
105 rwsem_wake(sem);
106}
107
108/*
109 * unlock after writing
110 */
111static inline void __up_write(struct rw_semaphore *sem)
112{
113 if (unlikely(atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
114 (atomic_t *)(&sem->count)) < 0))
115 rwsem_wake(sem);
116}
117
118/*
119 * implement atomic add functionality
120 */
121static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
122{
123 atomic_add(delta, (atomic_t *)(&sem->count));
124}
125
126/*
127 * downgrade write lock to read lock
128 */
129static inline void __downgrade_write(struct rw_semaphore *sem)
130{
131 int tmp;
132
133 tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
134 if (tmp < 0)
135 rwsem_downgrade_wake(sem);
136}
137
138/*
139 * implement exchange and add functionality
140 */
141static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
142{
143 return atomic_add_return(delta, (atomic_t *)(&sem->count));
144}
145
146static inline int rwsem_is_locked(struct rw_semaphore *sem)
147{
148 return (sem->count != 0);
149}
150
151#endif /* __KERNEL__ */
152#endif /* _ASM_POWERPC_RWSEM_H */