1 /*
2 * rwsem.h: R/W semaphores implemented using CAS
3 *
4 * Written by David S. Miller (davem@redhat.com), 2001.
5 * Derived from asm-i386/rwsem.h
6 */
7 #ifndef _SPARC64_RWSEM_H
8 #define _SPARC64_RWSEM_H
9
10 #ifndef _LINUX_RWSEM_H
11 #error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
12 #endif
13
14 #ifdef __KERNEL__
15
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)
22
23 /*
24 * lock for reading
25 */
__down_read(struct rw_semaphore * sem)26 static inline void __down_read(struct rw_semaphore *sem)
27 {
28 if (unlikely(atomic64_inc_return((atomic64_t *)(&sem->count)) <= 0L))
29 rwsem_down_read_failed(sem);
30 }
31
__down_read_trylock(struct rw_semaphore * sem)32 static inline int __down_read_trylock(struct rw_semaphore *sem)
33 {
34 long tmp;
35
36 while ((tmp = sem->count) >= 0L) {
37 if (tmp == cmpxchg(&sem->count, tmp,
38 tmp + RWSEM_ACTIVE_READ_BIAS)) {
39 return 1;
40 }
41 }
42 return 0;
43 }
44
45 /*
46 * lock for writing
47 */
__down_write_nested(struct rw_semaphore * sem,int subclass)48 static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
49 {
50 long tmp;
51
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);
56 }
57
__down_write(struct rw_semaphore * sem)58 static inline void __down_write(struct rw_semaphore *sem)
59 {
60 __down_write_nested(sem, 0);
61 }
62
__down_write_trylock(struct rw_semaphore * sem)63 static inline int __down_write_trylock(struct rw_semaphore *sem)
64 {
65 long tmp;
66
67 tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
68 RWSEM_ACTIVE_WRITE_BIAS);
69 return tmp == RWSEM_UNLOCKED_VALUE;
70 }
71
72 /*
73 * unlock after reading
74 */
__up_read(struct rw_semaphore * sem)75 static inline void __up_read(struct rw_semaphore *sem)
76 {
77 long tmp;
78
79 tmp = atomic64_dec_return((atomic64_t *)(&sem->count));
80 if (unlikely(tmp < -1L && (tmp & RWSEM_ACTIVE_MASK) == 0L))
81 rwsem_wake(sem);
82 }
83
84 /*
85 * unlock after writing
86 */
__up_write(struct rw_semaphore * sem)87 static inline void __up_write(struct rw_semaphore *sem)
88 {
89 if (unlikely(atomic64_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
90 (atomic64_t *)(&sem->count)) < 0L))
91 rwsem_wake(sem);
92 }
93
94 /*
95 * implement atomic add functionality
96 */
rwsem_atomic_add(long delta,struct rw_semaphore * sem)97 static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)
98 {
99 atomic64_add(delta, (atomic64_t *)(&sem->count));
100 }
101
102 /*
103 * downgrade write lock to read lock
104 */
__downgrade_write(struct rw_semaphore * sem)105 static inline void __downgrade_write(struct rw_semaphore *sem)
106 {
107 long tmp;
108
109 tmp = atomic64_add_return(-RWSEM_WAITING_BIAS, (atomic64_t *)(&sem->count));
110 if (tmp < 0L)
111 rwsem_downgrade_wake(sem);
112 }
113
114 /*
115 * implement exchange and add functionality
116 */
rwsem_atomic_update(long delta,struct rw_semaphore * sem)117 static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
118 {
119 return atomic64_add_return(delta, (atomic64_t *)(&sem->count));
120 }
121
122 #endif /* __KERNEL__ */
123
124 #endif /* _SPARC64_RWSEM_H */
125