1#ifndef _ASM_GENERIC_RWSEM_H
2#define _ASM_GENERIC_RWSEM_H
3
4#ifndef _LINUX_RWSEM_H
5#error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
6#endif
7
8#ifdef __KERNEL__
9
10/*
11 * R/W semaphores originally for PPC using the stuff in lib/rwsem.c.
12 * Adapted largely from include/asm-i386/rwsem.h
13 * by Paul Mackerras <paulus@samba.org>.
14 */
15
16/*
17 * the semaphore definition
18 */
19#ifdef CONFIG_64BIT
20# define RWSEM_ACTIVE_MASK		0xffffffffL
21#else
22# define RWSEM_ACTIVE_MASK		0x0000ffffL
23#endif
24
25#define RWSEM_UNLOCKED_VALUE		0x00000000L
26#define RWSEM_ACTIVE_BIAS		0x00000001L
27#define RWSEM_WAITING_BIAS		(-RWSEM_ACTIVE_MASK-1)
28#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
29#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
30
31/*
32 * lock for reading
33 */
34static inline void __down_read(struct rw_semaphore *sem)
35{
36	if (unlikely(atomic_long_inc_return((atomic_long_t *)&sem->count) <= 0))
37		rwsem_down_read_failed(sem);
38}
39
40static inline int __down_read_trylock(struct rw_semaphore *sem)
41{
42	long tmp;
43
44	while ((tmp = sem->count) >= 0) {
45		if (tmp == cmpxchg(&sem->count, tmp,
46				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
47			return 1;
48		}
49	}
50	return 0;
51}
52
53/*
54 * lock for writing
55 */
56static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
57{
58	long tmp;
59
60	tmp = atomic_long_add_return(RWSEM_ACTIVE_WRITE_BIAS,
61				     (atomic_long_t *)&sem->count);
62	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
63		rwsem_down_write_failed(sem);
64}
65
66static inline void __down_write(struct rw_semaphore *sem)
67{
68	__down_write_nested(sem, 0);
69}
70
71static inline int __down_write_trylock(struct rw_semaphore *sem)
72{
73	long tmp;
74
75	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
76		      RWSEM_ACTIVE_WRITE_BIAS);
77	return tmp == RWSEM_UNLOCKED_VALUE;
78}
79
80/*
81 * unlock after reading
82 */
83static inline void __up_read(struct rw_semaphore *sem)
84{
85	long tmp;
86
87	tmp = atomic_long_dec_return((atomic_long_t *)&sem->count);
88	if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
89		rwsem_wake(sem);
90}
91
92/*
93 * unlock after writing
94 */
95static inline void __up_write(struct rw_semaphore *sem)
96{
97	if (unlikely(atomic_long_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
98				 (atomic_long_t *)&sem->count) < 0))
99		rwsem_wake(sem);
100}
101
102/*
103 * implement atomic add functionality
104 */
105static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)
106{
107	atomic_long_add(delta, (atomic_long_t *)&sem->count);
108}
109
110/*
111 * downgrade write lock to read lock
112 */
113static inline void __downgrade_write(struct rw_semaphore *sem)
114{
115	long tmp;
116
117	tmp = atomic_long_add_return(-RWSEM_WAITING_BIAS,
118				     (atomic_long_t *)&sem->count);
119	if (tmp < 0)
120		rwsem_downgrade_wake(sem);
121}
122
123/*
124 * implement exchange and add functionality
125 */
126static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
127{
128	return atomic_long_add_return(delta, (atomic_long_t *)&sem->count);
129}
130
131#endif	/* __KERNEL__ */
132#endif	/* _ASM_GENERIC_RWSEM_H */
133