2 * include/asm-xtensa/rwsem.h
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
8 * Largely copied from include/asm-ppc/rwsem.h
10 * Copyright (C) 2001 - 2005 Tensilica Inc.
13 #ifndef _XTENSA_RWSEM_H
14 #define _XTENSA_RWSEM_H
16 #include <linux/list.h>
17 #include <linux/spinlock.h>
18 #include <asm/atomic.h>
19 #include <asm/system.h>
22 * the semaphore definition
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)
33 struct list_head wait_list
;
36 #define __RWSEM_INITIALIZER(name) \
37 { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
38 LIST_HEAD_INIT((name).wait_list) }
40 #define DECLARE_RWSEM(name) \
41 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
43 extern struct rw_semaphore
*rwsem_down_read_failed(struct rw_semaphore
*sem
);
44 extern struct rw_semaphore
*rwsem_down_write_failed(struct rw_semaphore
*sem
);
45 extern struct rw_semaphore
*rwsem_wake(struct rw_semaphore
*sem
);
46 extern struct rw_semaphore
*rwsem_downgrade_wake(struct rw_semaphore
*sem
);
48 static inline void init_rwsem(struct rw_semaphore
*sem
)
50 sem
->count
= RWSEM_UNLOCKED_VALUE
;
51 spin_lock_init(&sem
->wait_lock
);
52 INIT_LIST_HEAD(&sem
->wait_list
);
58 static inline void __down_read(struct rw_semaphore
*sem
)
60 if (atomic_add_return(1,(atomic_t
*)(&sem
->count
)) > 0)
63 rwsem_down_read_failed(sem
);
66 static inline int __down_read_trylock(struct rw_semaphore
*sem
)
70 while ((tmp
= sem
->count
) >= 0) {
71 if (tmp
== cmpxchg(&sem
->count
, tmp
,
72 tmp
+ RWSEM_ACTIVE_READ_BIAS
)) {
83 static inline void __down_write(struct rw_semaphore
*sem
)
87 tmp
= atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS
,
88 (atomic_t
*)(&sem
->count
));
89 if (tmp
== RWSEM_ACTIVE_WRITE_BIAS
)
92 rwsem_down_write_failed(sem
);
95 static inline int __down_write_trylock(struct rw_semaphore
*sem
)
99 tmp
= cmpxchg(&sem
->count
, RWSEM_UNLOCKED_VALUE
,
100 RWSEM_ACTIVE_WRITE_BIAS
);
102 return tmp
== RWSEM_UNLOCKED_VALUE
;
106 * unlock after reading
108 static inline void __up_read(struct rw_semaphore
*sem
)
113 tmp
= atomic_sub_return(1,(atomic_t
*)(&sem
->count
));
114 if (tmp
< -1 && (tmp
& RWSEM_ACTIVE_MASK
) == 0)
119 * unlock after writing
121 static inline void __up_write(struct rw_semaphore
*sem
)
124 if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS
,
125 (atomic_t
*)(&sem
->count
)) < 0)
130 * implement atomic add functionality
132 static inline void rwsem_atomic_add(int delta
, struct rw_semaphore
*sem
)
134 atomic_add(delta
, (atomic_t
*)(&sem
->count
));
138 * downgrade write lock to read lock
140 static inline void __downgrade_write(struct rw_semaphore
*sem
)
145 tmp
= atomic_add_return(-RWSEM_WAITING_BIAS
, (atomic_t
*)(&sem
->count
));
147 rwsem_downgrade_wake(sem
);
151 * implement exchange and add functionality
153 static inline int rwsem_atomic_update(int delta
, struct rw_semaphore
*sem
)
156 return atomic_add_return(delta
, (atomic_t
*)(&sem
->count
));
159 static inline int rwsem_is_locked(struct rw_semaphore
*sem
)
161 return (sem
->count
!= 0);
164 #endif /* _XTENSA_RWSEM_H */
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