1 /* $Id: semaphore.h,v 1.12 1999/12/08 22:05:10 harald Exp $
2 *
3 * SMP- and interrupt-safe semaphores..
4 *
5 * This file is subject to the terms and conditions of the GNU General Public
6 * License. See the file "COPYING" in the main directory of this archive
7 * for more details.
8 *
9 * (C) Copyright 1996 Linus Torvalds
10 * (C) Copyright 1998, 1999, 2000 Ralf Baechle
11 * (C) Copyright 1999, 2000 Silicon Graphics, Inc.
12 */
13 #ifndef _ASM_SEMAPHORE_H
14 #define _ASM_SEMAPHORE_H
15
16 #include <asm/system.h>
17 #include <asm/atomic.h>
18 #include <linux/spinlock.h>
19 #include <linux/wait.h>
20 #include <linux/config.h>
21
22 struct semaphore {
23 #ifdef __MIPSEB__
24 atomic_t count;
25 atomic_t waking;
26 #else
27 atomic_t waking;
28 atomic_t count;
29 #endif
30 wait_queue_head_t wait;
31 #if WAITQUEUE_DEBUG
32 long __magic;
33 #endif
34 } __attribute__((aligned(8)));
35
36 #if WAITQUEUE_DEBUG
37 # define __SEM_DEBUG_INIT(name) \
38 , (long)&(name).__magic
39 #else
40 # define __SEM_DEBUG_INIT(name)
41 #endif
42
43 #ifdef __MIPSEB__
44 #define __SEMAPHORE_INITIALIZER(name,count) \
45 { ATOMIC_INIT(count), ATOMIC_INIT(0), __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
46 __SEM_DEBUG_INIT(name) }
47 #else
48 #define __SEMAPHORE_INITIALIZER(name,count) \
49 { ATOMIC_INIT(0), ATOMIC_INIT(count), __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
50 __SEM_DEBUG_INIT(name) }
51 #endif
52
53 #define __MUTEX_INITIALIZER(name) \
54 __SEMAPHORE_INITIALIZER(name,1)
55
56 #define __DECLARE_SEMAPHORE_GENERIC(name,count) \
57 struct semaphore name = __SEMAPHORE_INITIALIZER(name,count)
58
59 #define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1)
60 #define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0)
61
62 extern inline void sema_init (struct semaphore *sem, int val)
63 {
64 atomic_set(&sem->count, val);
65 atomic_set(&sem->waking, 0);
66 init_waitqueue_head(&sem->wait);
67 #if WAITQUEUE_DEBUG
68 sem->__magic = (long)&sem->__magic;
69 #endif
70 }
71
72 static inline void init_MUTEX (struct semaphore *sem)
73 {
74 sema_init(sem, 1);
75 }
76
77 static inline void init_MUTEX_LOCKED (struct semaphore *sem)
78 {
79 sema_init(sem, 0);
80 }
81
82 asmlinkage void __down(struct semaphore * sem);
83 asmlinkage int __down_interruptible(struct semaphore * sem);
84 asmlinkage int __down_trylock(struct semaphore * sem);
85 asmlinkage void __up(struct semaphore * sem);
86
87 extern inline void down(struct semaphore * sem)
88 {
89 #if WAITQUEUE_DEBUG
90 CHECK_MAGIC(sem->__magic);
91 #endif
92 if (atomic_dec_return(&sem->count) < 0)
93 __down(sem);
94 }
95
96 extern inline int down_interruptible(struct semaphore * sem)
97 {
98 int ret = 0;
99
100 #if WAITQUEUE_DEBUG
101 CHECK_MAGIC(sem->__magic);
102 #endif
103 if (atomic_dec_return(&sem->count) < 0)
104 ret = __down_interruptible(sem);
105 return ret;
106 }
107
108 #if !defined(CONFIG_CPU_HAS_LLSC)
109
110 extern inline int down_trylock(struct semaphore * sem)
111 {
112 int ret = 0;
113 if (atomic_dec_return(&sem->count) < 0)
114 ret = __down_trylock(sem);
115 return ret;
116 }
117
118 #else
119
120 /*
121 * down_trylock returns 0 on success, 1 if we failed to get the lock.
122 *
123 * We must manipulate count and waking simultaneously and atomically.
124 * Here, we this by using ll/sc on the pair of 32-bit words. This
125 * won't work on MIPS32 platforms, however, and must be rewritten.
126 *
127 * Pseudocode:
128 *
129 * Decrement(sem->count)
130 * If(sem->count >=0) {
131 * Return(SUCCESS) // resource is free
132 * } else {
133 * If(sem->waking <= 0) { // if no wakeup pending
134 * Increment(sem->count) // undo decrement
135 * Return(FAILURE)
136 * } else {
137 * Decrement(sem->waking) // otherwise "steal" wakeup
138 * Return(SUCCESS)
139 * }
140 * }
141 */
142 extern inline int down_trylock(struct semaphore * sem)
143 {
144 long ret, tmp, tmp2, sub;
145
146 #if WAITQUEUE_DEBUG
147 CHECK_MAGIC(sem->__magic);
148 #endif
149
150 __asm__ __volatile__("
151 .set mips3
152
153 0: lld %1, %4
154 dli %3, 0x0000000100000000
155 dsubu %1, %3
156 li %0, 0
157 bgez %1, 2f
158 sll %2, %1, 0
159 blez %2, 1f
160 daddiu %1, %1, -1
161 b 2f
162 1:
163 daddu %1, %1, %3
164 li %0, 1
165 2:
166 scd %1, %4
167 beqz %1, 0b
168
169 .set mips0"
170 : "=&r"(ret), "=&r"(tmp), "=&r"(tmp2), "=&r"(sub)
171 : "m"(*sem)
172 : "memory");
173
174 return ret;
175 }
176
177 #endif
178
179 /*
180 * Note! This is subtle. We jump to wake people up only if
181 * the semaphore was negative (== somebody was waiting on it).
182 */
183 extern inline void up(struct semaphore * sem)
184 {
185 #if WAITQUEUE_DEBUG
186 CHECK_MAGIC(sem->__magic);
187 #endif
188 if (atomic_inc_return(&sem->count) <= 0)
189 __up(sem);
190 }
191
192 /*
193 * rw mutexes (should that be mutices? =) -- throw rw spinlocks and
194 * semaphores together, and this is what we end up with...
195 *
196 * The lock is initialized to BIAS. This way, a writer subtracts BIAS ands
197 * gets 0 for the case of an uncontended lock. Readers decrement by 1 and
198 * see a positive value when uncontended, negative if there are writers
199 * waiting (in which case it goes to sleep).
200 *
201 * The value 0x01000000 supports up to 128 processors and lots of processes.
202 * BIAS must be chosen such that subtracting BIAS once per CPU will result
203 * in the int remaining negative. In terms of fairness, this should result
204 * in the lock flopping back and forth between readers and writers under
205 * heavy use.
206 *
207 * Once we start supporting machines with more than 128 CPUs, we should go
208 * for using a 64bit atomic type instead of 32bit as counter. We shall
209 * probably go for bias 0x80000000 then, so that single sethi can set it.
210 * */
211
212 #define RW_LOCK_BIAS 0x01000000
213
214 struct rw_semaphore {
215 atomic_t count;
216 /* bit 0 means read bias granted;
217 bit 1 means write bias granted. */
218 unsigned granted;
219 wait_queue_head_t wait;
220 wait_queue_head_t write_bias_wait;
221 #if WAITQUEUE_DEBUG
222 long __magic;
223 atomic_t readers;
224 atomic_t writers;
225 #endif
226 };
227
228 #if WAITQUEUE_DEBUG
229 #define __RWSEM_DEBUG_INIT , ATOMIC_INIT(0), ATOMIC_INIT(0)
230 #else
231 #define __RWSEM_DEBUG_INIT /* */
232 #endif
233
234 #define __RWSEM_INITIALIZER(name,count) \
235 { ATOMIC_INIT(count), 0, \
236 __WAIT_QUEUE_HEAD_INITIALIZER((name).wait), \
237 __WAIT_QUEUE_HEAD_INITIALIZER((name).write_bias_wait) \
238 __SEM_DEBUG_INIT(name) __RWSEM_DEBUG_INIT }
239
240 #define __DECLARE_RWSEM_GENERIC(name,count) \
241 struct rw_semaphore name = __RWSEM_INITIALIZER(name,count)
242
243 #define DECLARE_RWSEM(name) \
244 __DECLARE_RWSEM_GENERIC(name, RW_LOCK_BIAS)
245 #define DECLARE_RWSEM_READ_LOCKED(name) \
246 __DECLARE_RWSEM_GENERIC(name, RW_LOCK_BIAS-1)
247 #define DECLARE_RWSEM_WRITE_LOCKED(name) \
248 __DECLARE_RWSEM_GENERIC(name, 0)
249
250 extern inline void init_rwsem(struct rw_semaphore *sem)
251 {
252 atomic_set(&sem->count, RW_LOCK_BIAS);
253 sem->granted = 0;
254 init_waitqueue_head(&sem->wait);
255 init_waitqueue_head(&sem->write_bias_wait);
256 #if WAITQUEUE_DEBUG
257 sem->__magic = (long)&sem->__magic;
258 atomic_set(&sem->readers, 0);
259 atomic_set(&sem->writers, 0);
260 #endif
261 }
262
263 /* The expensive part is outlined. */
264 extern void __down_read(struct rw_semaphore *sem, int count);
265 extern void __down_write(struct rw_semaphore *sem, int count);
266 extern void __rwsem_wake(struct rw_semaphore *sem, unsigned long readers);
267
268 extern inline void down_read(struct rw_semaphore *sem)
269 {
270 int count;
271
272 #if WAITQUEUE_DEBUG
273 CHECK_MAGIC(sem->__magic);
274 #endif
275
276 count = atomic_dec_return(&sem->count);
277 if (count < 0) {
278 __down_read(sem, count);
279 }
280 mb();
281
282 #if WAITQUEUE_DEBUG
283 if (sem->granted & 2)
284 BUG();
285 if (atomic_read(&sem->writers))
286 BUG();
287 atomic_inc(&sem->readers);
288 #endif
289 }
290
291 extern inline void down_write(struct rw_semaphore *sem)
292 {
293 int count;
294
295 #if WAITQUEUE_DEBUG
296 CHECK_MAGIC(sem->__magic);
297 #endif
298
299 count = atomic_sub_return(RW_LOCK_BIAS, &sem->count);
300 if (count) {
301 __down_write(sem, count);
302 }
303 mb();
304
305 #if WAITQUEUE_DEBUG
306 if (atomic_read(&sem->writers))
307 BUG();
308 if (atomic_read(&sem->readers))
309 BUG();
310 if (sem->granted & 3)
311 BUG();
312 atomic_inc(&sem->writers);
313 #endif
314 }
315
316 /* When a reader does a release, the only significant case is when
317 there was a writer waiting, and we've bumped the count to 0: we must
318 wake the writer up. */
319
320 extern inline void up_read(struct rw_semaphore *sem)
321 {
322 #if WAITQUEUE_DEBUG
323 CHECK_MAGIC(sem->__magic);
324 if (sem->granted & 2)
325 BUG();
326 if (atomic_read(&sem->writers))
327 BUG();
328 atomic_dec(&sem->readers);
329 #endif
330
331 mb();
332 if (atomic_inc_return(&sem->count) == 0)
333 __rwsem_wake(sem, 0);
334 }
335
336 /*
337 * Releasing the writer is easy -- just release it and wake up any sleepers.
338 */
339 extern inline void up_write(struct rw_semaphore *sem)
340 {
341 int count;
342
343 #if WAITQUEUE_DEBUG
344 CHECK_MAGIC(sem->__magic);
345 if (sem->granted & 3)
346 BUG();
347 if (atomic_read(&sem->readers))
348 BUG();
349 if (atomic_read(&sem->writers) != 1)
350 BUG();
351 atomic_dec(&sem->writers);
352 #endif
353
354 mb();
355 count = atomic_add_return(RW_LOCK_BIAS, &sem->count);
356 if (count - RW_LOCK_BIAS < 0 && count >= 0) {
357 /* Only do the wake if we're no longer negative. */
358 __rwsem_wake(sem, count);
359 }
360 }
361
362 #endif /* _ASM_SEMAPHORE_H */
363
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