2 * rwsem.h: R/W semaphores implemented using CAS
4 * Written by David S. Miller (davem@redhat.com), 2001.
5 * Derived from asm-i386/rwsem.h
7 #ifndef _SPARC64_RWSEM_H
8 #define _SPARC64_RWSEM_H
10 #ifndef _LINUX_RWSEM_H
11 #error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
16 #define RWSEM_UNLOCKED_VALUE 0x00000000L
17 #define RWSEM_ACTIVE_BIAS 0x00000001L
18 #define RWSEM_ACTIVE_MASK 0xffffffffL
19 #define RWSEM_WAITING_BIAS (-RWSEM_ACTIVE_MASK-1)
20 #define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
21 #define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
26 static inline void __down_read(struct rw_semaphore
*sem
)
28 if (unlikely(atomic64_inc_return((atomic64_t
*)(&sem
->count
)) <= 0L))
29 rwsem_down_read_failed(sem
);
32 static inline int __down_read_trylock(struct rw_semaphore
*sem
)
36 while ((tmp
= sem
->count
) >= 0L) {
37 if (tmp
== cmpxchg(&sem
->count
, tmp
,
38 tmp
+ RWSEM_ACTIVE_READ_BIAS
)) {
48 static inline void __down_write(struct rw_semaphore
*sem
)
52 tmp
= atomic64_add_return(RWSEM_ACTIVE_WRITE_BIAS
,
53 (atomic64_t
*)(&sem
->count
));
54 if (unlikely(tmp
!= RWSEM_ACTIVE_WRITE_BIAS
))
55 rwsem_down_write_failed(sem
);
58 static inline int __down_write_trylock(struct rw_semaphore
*sem
)
62 tmp
= cmpxchg(&sem
->count
, RWSEM_UNLOCKED_VALUE
,
63 RWSEM_ACTIVE_WRITE_BIAS
);
64 return tmp
== RWSEM_UNLOCKED_VALUE
;
68 * unlock after reading
70 static inline void __up_read(struct rw_semaphore
*sem
)
74 tmp
= atomic64_dec_return((atomic64_t
*)(&sem
->count
));
75 if (unlikely(tmp
< -1L && (tmp
& RWSEM_ACTIVE_MASK
) == 0L))
80 * unlock after writing
82 static inline void __up_write(struct rw_semaphore
*sem
)
84 if (unlikely(atomic64_sub_return(RWSEM_ACTIVE_WRITE_BIAS
,
85 (atomic64_t
*)(&sem
->count
)) < 0L))
90 * implement atomic add functionality
92 static inline void rwsem_atomic_add(long delta
, struct rw_semaphore
*sem
)
94 atomic64_add(delta
, (atomic64_t
*)(&sem
->count
));
98 * downgrade write lock to read lock
100 static inline void __downgrade_write(struct rw_semaphore
*sem
)
104 tmp
= atomic64_add_return(-RWSEM_WAITING_BIAS
, (atomic64_t
*)(&sem
->count
));
106 rwsem_downgrade_wake(sem
);
110 * implement exchange and add functionality
112 static inline long rwsem_atomic_update(long delta
, struct rw_semaphore
*sem
)
114 return atomic64_add_return(delta
, (atomic64_t
*)(&sem
->count
));
117 #endif /* __KERNEL__ */
119 #endif /* _SPARC64_RWSEM_H */
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