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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
2 * asm-ia64/rwsem.h: R/W semaphores for ia64
3 *
4 * Copyright (C) 2003 Ken Chen <kenneth.w.chen@intel.com>
5 * Copyright (C) 2003 Asit Mallick <asit.k.mallick@intel.com>
6 *
7 * Based on asm-i386/rwsem.h and other architecture implementation.
8 *
9 * The MSW of the count is the negated number of active writers and
10 * waiting lockers, and the LSW is the total number of active locks.
11 *
12 * The lock count is initialized to 0 (no active and no waiting lockers).
13 *
14 * When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case
15 * of an uncontended lock. Readers increment by 1 and see a positive value
16 * when uncontended, negative if there are writers (and maybe) readers
17 * waiting (in which case it goes to sleep).
18 */
19
20#ifndef _ASM_IA64_RWSEM_H
21#define _ASM_IA64_RWSEM_H
22
23#include <linux/list.h>
24#include <linux/spinlock.h>
25
26#include <asm/intrinsics.h>
27
28/*
29 * the semaphore definition
30 */
31struct rw_semaphore {
32 signed int count;
33 spinlock_t wait_lock;
34 struct list_head wait_list;
35#if RWSEM_DEBUG
36 int debug;
37#endif
38};
39
40#define RWSEM_UNLOCKED_VALUE 0x00000000
41#define RWSEM_ACTIVE_BIAS 0x00000001
42#define RWSEM_ACTIVE_MASK 0x0000ffff
43#define RWSEM_WAITING_BIAS (-0x00010000)
44#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
45#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
46
47/*
48 * initialization
49 */
50#if RWSEM_DEBUG
51#define __RWSEM_DEBUG_INIT , 0
52#else
53#define __RWSEM_DEBUG_INIT /* */
54#endif
55
56#define __RWSEM_INITIALIZER(name) \
57 { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
58 LIST_HEAD_INIT((name).wait_list) \
59 __RWSEM_DEBUG_INIT }
60
61#define DECLARE_RWSEM(name) \
62 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
63
64extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
65extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
66extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
67extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
68
69static inline void
70init_rwsem (struct rw_semaphore *sem)
71{
72 sem->count = RWSEM_UNLOCKED_VALUE;
73 spin_lock_init(&sem->wait_lock);
74 INIT_LIST_HEAD(&sem->wait_list);
75#if RWSEM_DEBUG
76 sem->debug = 0;
77#endif
78}
79
80/*
81 * lock for reading
82 */
83static inline void
84__down_read (struct rw_semaphore *sem)
85{
86 int result = ia64_fetchadd4_acq((unsigned int *)&sem->count, 1);
87
88 if (result < 0)
89 rwsem_down_read_failed(sem);
90}
91
92/*
93 * lock for writing
94 */
95static inline void
96__down_write (struct rw_semaphore *sem)
97{
98 int old, new;
99
100 do {
101 old = sem->count;
102 new = old + RWSEM_ACTIVE_WRITE_BIAS;
103 } while (cmpxchg_acq(&sem->count, old, new) != old);
104
105 if (old != 0)
106 rwsem_down_write_failed(sem);
107}
108
109/*
110 * unlock after reading
111 */
112static inline void
113__up_read (struct rw_semaphore *sem)
114{
115 int result = ia64_fetchadd4_rel((unsigned int *)&sem->count, -1);
116
117 if (result < 0 && (--result & RWSEM_ACTIVE_MASK) == 0)
118 rwsem_wake(sem);
119}
120
121/*
122 * unlock after writing
123 */
124static inline void
125__up_write (struct rw_semaphore *sem)
126{
127 int old, new;
128
129 do {
130 old = sem->count;
131 new = old - RWSEM_ACTIVE_WRITE_BIAS;
132 } while (cmpxchg_rel(&sem->count, old, new) != old);
133
134 if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0)
135 rwsem_wake(sem);
136}
137
138/*
139 * trylock for reading -- returns 1 if successful, 0 if contention
140 */
141static inline int
142__down_read_trylock (struct rw_semaphore *sem)
143{
144 int tmp;
145 while ((tmp = sem->count) >= 0) {
146 if (tmp == cmpxchg_acq(&sem->count, tmp, tmp+1)) {
147 return 1;
148 }
149 }
150 return 0;
151}
152
153/*
154 * trylock for writing -- returns 1 if successful, 0 if contention
155 */
156static inline int
157__down_write_trylock (struct rw_semaphore *sem)
158{
159 int tmp = cmpxchg_acq(&sem->count, RWSEM_UNLOCKED_VALUE,
160 RWSEM_ACTIVE_WRITE_BIAS);
161 return tmp == RWSEM_UNLOCKED_VALUE;
162}
163
164/*
165 * downgrade write lock to read lock
166 */
167static inline void
168__downgrade_write (struct rw_semaphore *sem)
169{
170 int old, new;
171
172 do {
173 old = sem->count;
174 new = old - RWSEM_WAITING_BIAS;
175 } while (cmpxchg_rel(&sem->count, old, new) != old);
176
177 if (old < 0)
178 rwsem_downgrade_wake(sem);
179}
180
181/*
182 * Implement atomic add functionality. These used to be "inline" functions, but GCC v3.1
183 * doesn't quite optimize this stuff right and ends up with bad calls to fetchandadd.
184 */
185#define rwsem_atomic_add(delta, sem) atomic_add(delta, (atomic_t *)(&(sem)->count))
186#define rwsem_atomic_update(delta, sem) atomic_add_return(delta, (atomic_t *)(&(sem)->count))
187
188#endif /* _ASM_IA64_RWSEM_H */