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Linux/include/asm-alpha/rwsem.h

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  1 #ifndef _ALPHA_RWSEM_H
  2 #define _ALPHA_RWSEM_H
  3 
  4 /*
  5  * Written by Ivan Kokshaysky <ink@jurassic.park.msu.ru>, 2001.
  6  * Based on asm-alpha/semaphore.h and asm-i386/rwsem.h
  7  */
  8 
  9 #ifndef _LINUX_RWSEM_H
 10 #error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
 11 #endif
 12 
 13 #ifdef __KERNEL__
 14 
 15 #include <linux/compiler.h>
 16 #include <linux/list.h>
 17 #include <linux/spinlock.h>
 18 
 19 struct rwsem_waiter;
 20 
 21 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
 22 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
 23 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
 24 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
 25 
 26 /*
 27  * the semaphore definition
 28  */
 29 struct rw_semaphore {
 30         long                    count;
 31 #define RWSEM_UNLOCKED_VALUE            0x0000000000000000L
 32 #define RWSEM_ACTIVE_BIAS               0x0000000000000001L
 33 #define RWSEM_ACTIVE_MASK               0x00000000ffffffffL
 34 #define RWSEM_WAITING_BIAS              (-0x0000000100000000L)
 35 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
 36 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
 37         spinlock_t              wait_lock;
 38         struct list_head        wait_list;
 39 #if RWSEM_DEBUG
 40         int                     debug;
 41 #endif
 42 };
 43 
 44 #if RWSEM_DEBUG
 45 #define __RWSEM_DEBUG_INIT      , 0
 46 #else
 47 #define __RWSEM_DEBUG_INIT      /* */
 48 #endif
 49 
 50 #define __RWSEM_INITIALIZER(name) \
 51         { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
 52         LIST_HEAD_INIT((name).wait_list) __RWSEM_DEBUG_INIT }
 53 
 54 #define DECLARE_RWSEM(name) \
 55         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
 56 
 57 static inline void init_rwsem(struct rw_semaphore *sem)
 58 {
 59         sem->count = RWSEM_UNLOCKED_VALUE;
 60         spin_lock_init(&sem->wait_lock);
 61         INIT_LIST_HEAD(&sem->wait_list);
 62 #if RWSEM_DEBUG
 63         sem->debug = 0;
 64 #endif
 65 }
 66 
 67 static inline void __down_read(struct rw_semaphore *sem)
 68 {
 69         long oldcount;
 70 #ifndef CONFIG_SMP
 71         oldcount = sem->count;
 72         sem->count += RWSEM_ACTIVE_READ_BIAS;
 73 #else
 74         long temp;
 75         __asm__ __volatile__(
 76         "1:     ldq_l   %0,%1\n"
 77         "       addq    %0,%3,%2\n"
 78         "       stq_c   %2,%1\n"
 79         "       beq     %2,2f\n"
 80         "       mb\n"
 81         ".subsection 2\n"
 82         "2:     br      1b\n"
 83         ".previous"
 84         :"=&r" (oldcount), "=m" (sem->count), "=&r" (temp)
 85         :"Ir" (RWSEM_ACTIVE_READ_BIAS), "m" (sem->count) : "memory");
 86 #endif
 87         if (unlikely(oldcount < 0))
 88                 rwsem_down_read_failed(sem);
 89 }
 90 
 91 /*
 92  * trylock for reading -- returns 1 if successful, 0 if contention
 93  */
 94 static inline int __down_read_trylock(struct rw_semaphore *sem)
 95 {
 96         long old, new, res;
 97 
 98         res = sem->count;
 99         do {
100                 new = res + RWSEM_ACTIVE_READ_BIAS;
101                 if (new <= 0)
102                         break;
103                 old = res;
104                 res = cmpxchg(&sem->count, old, new);
105         } while (res != old);
106         return res >= 0 ? 1 : 0;
107 }
108 
109 static inline void __down_write(struct rw_semaphore *sem)
110 {
111         long oldcount;
112 #ifndef CONFIG_SMP
113         oldcount = sem->count;
114         sem->count += RWSEM_ACTIVE_WRITE_BIAS;
115 #else
116         long temp;
117         __asm__ __volatile__(
118         "1:     ldq_l   %0,%1\n"
119         "       addq    %0,%3,%2\n"
120         "       stq_c   %2,%1\n"
121         "       beq     %2,2f\n"
122         "       mb\n"
123         ".subsection 2\n"
124         "2:     br      1b\n"
125         ".previous"
126         :"=&r" (oldcount), "=m" (sem->count), "=&r" (temp)
127         :"Ir" (RWSEM_ACTIVE_WRITE_BIAS), "m" (sem->count) : "memory");
128 #endif
129         if (unlikely(oldcount))
130                 rwsem_down_write_failed(sem);
131 }
132 
133 /*
134  * trylock for writing -- returns 1 if successful, 0 if contention
135  */
136 static inline int __down_write_trylock(struct rw_semaphore *sem)
137 {
138         long ret = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
139                            RWSEM_ACTIVE_WRITE_BIAS);
140         if (ret == RWSEM_UNLOCKED_VALUE)
141                 return 1;
142         return 0;
143 }
144 
145 static inline void __up_read(struct rw_semaphore *sem)
146 {
147         long oldcount;
148 #ifndef CONFIG_SMP
149         oldcount = sem->count;
150         sem->count -= RWSEM_ACTIVE_READ_BIAS;
151 #else
152         long temp;
153         __asm__ __volatile__(
154         "       mb\n"
155         "1:     ldq_l   %0,%1\n"
156         "       subq    %0,%3,%2\n"
157         "       stq_c   %2,%1\n"
158         "       beq     %2,2f\n"
159         ".subsection 2\n"
160         "2:     br      1b\n"
161         ".previous"
162         :"=&r" (oldcount), "=m" (sem->count), "=&r" (temp)
163         :"Ir" (RWSEM_ACTIVE_READ_BIAS), "m" (sem->count) : "memory");
164 #endif
165         if (unlikely(oldcount < 0))
166                 if ((int)oldcount - RWSEM_ACTIVE_READ_BIAS == 0)
167                         rwsem_wake(sem);
168 }
169 
170 static inline void __up_write(struct rw_semaphore *sem)
171 {
172         long count;
173 #ifndef CONFIG_SMP
174         sem->count -= RWSEM_ACTIVE_WRITE_BIAS;
175         count = sem->count;
176 #else
177         long temp;
178         __asm__ __volatile__(
179         "       mb\n"
180         "1:     ldq_l   %0,%1\n"
181         "       subq    %0,%3,%2\n"
182         "       stq_c   %2,%1\n"
183         "       beq     %2,2f\n"
184         "       subq    %0,%3,%0\n"
185         ".subsection 2\n"
186         "2:     br      1b\n"
187         ".previous"
188         :"=&r" (count), "=m" (sem->count), "=&r" (temp)
189         :"Ir" (RWSEM_ACTIVE_WRITE_BIAS), "m" (sem->count) : "memory");
190 #endif
191         if (unlikely(count))
192                 if ((int)count == 0)
193                         rwsem_wake(sem);
194 }
195 
196 /*
197  * downgrade write lock to read lock
198  */
199 static inline void __downgrade_write(struct rw_semaphore *sem)
200 {
201         long oldcount;
202 #ifndef CONFIG_SMP
203         oldcount = sem->count;
204         sem->count -= RWSEM_WAITING_BIAS;
205 #else
206         long temp;
207         __asm__ __volatile__(
208         "1:     ldq_l   %0,%1\n"
209         "       addq    %0,%3,%2\n"
210         "       stq_c   %2,%1\n"
211         "       beq     %2,2f\n"
212         "       mb\n"
213         ".subsection 2\n"
214         "2:     br      1b\n"
215         ".previous"
216         :"=&r" (oldcount), "=m" (sem->count), "=&r" (temp)
217         :"Ir" (-RWSEM_WAITING_BIAS), "m" (sem->count) : "memory");
218 #endif
219         if (unlikely(oldcount < 0))
220                 rwsem_downgrade_wake(sem);
221 }
222 
223 static inline void rwsem_atomic_add(long val, struct rw_semaphore *sem)
224 {
225 #ifndef CONFIG_SMP
226         sem->count += val;
227 #else
228         long temp;
229         __asm__ __volatile__(
230         "1:     ldq_l   %0,%1\n"
231         "       addq    %0,%2,%0\n"
232         "       stq_c   %0,%1\n"
233         "       beq     %0,2f\n"
234         ".subsection 2\n"
235         "2:     br      1b\n"
236         ".previous"
237         :"=&r" (temp), "=m" (sem->count)
238         :"Ir" (val), "m" (sem->count));
239 #endif
240 }
241 
242 static inline long rwsem_atomic_update(long val, struct rw_semaphore *sem)
243 {
244 #ifndef CONFIG_SMP
245         sem->count += val;
246         return sem->count;
247 #else
248         long ret, temp;
249         __asm__ __volatile__(
250         "1:     ldq_l   %0,%1\n"
251         "       addq    %0,%3,%2\n"
252         "       addq    %0,%3,%0\n"
253         "       stq_c   %2,%1\n"
254         "       beq     %2,2f\n"
255         ".subsection 2\n"
256         "2:     br      1b\n"
257         ".previous"
258         :"=&r" (ret), "=m" (sem->count), "=&r" (temp)
259         :"Ir" (val), "m" (sem->count));
260 
261         return ret;
262 #endif
263 }
264 
265 #endif /* __KERNEL__ */
266 #endif /* _ALPHA_RWSEM_H */
267 

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