1/*
2 * include/asm-sh/rwsem.h: R/W semaphores for SH using the stuff
3 * in lib/rwsem.c.
4 */
5
6#ifndef _ASM_SH_RWSEM_H
7#define _ASM_SH_RWSEM_H
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#define RWSEM_UNLOCKED_VALUE		0x00000000
16#define RWSEM_ACTIVE_BIAS		0x00000001
17#define RWSEM_ACTIVE_MASK		0x0000ffff
18#define RWSEM_WAITING_BIAS		(-0x00010000)
19#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
20#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
21
22/*
23 * lock for reading
24 */
25static inline void __down_read(struct rw_semaphore *sem)
26{
27	if (atomic_inc_return((atomic_t *)(&sem->count)) > 0)
28		smp_wmb();
29	else
30		rwsem_down_read_failed(sem);
31}
32
33static inline int __down_read_trylock(struct rw_semaphore *sem)
34{
35	int tmp;
36
37	while ((tmp = sem->count) >= 0) {
38		if (tmp == cmpxchg(&sem->count, tmp,
39				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
40			smp_wmb();
41			return 1;
42		}
43	}
44	return 0;
45}
46
47/*
48 * lock for writing
49 */
50static inline void __down_write(struct rw_semaphore *sem)
51{
52	int tmp;
53
54	tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
55				(atomic_t *)(&sem->count));
56	if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
57		smp_wmb();
58	else
59		rwsem_down_write_failed(sem);
60}
61
62static inline int __down_write_trylock(struct rw_semaphore *sem)
63{
64	int tmp;
65
66	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
67		      RWSEM_ACTIVE_WRITE_BIAS);
68	smp_wmb();
69	return tmp == RWSEM_UNLOCKED_VALUE;
70}
71
72/*
73 * unlock after reading
74 */
75static inline void __up_read(struct rw_semaphore *sem)
76{
77	int tmp;
78
79	smp_wmb();
80	tmp = atomic_dec_return((atomic_t *)(&sem->count));
81	if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
82		rwsem_wake(sem);
83}
84
85/*
86 * unlock after writing
87 */
88static inline void __up_write(struct rw_semaphore *sem)
89{
90	smp_wmb();
91	if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
92			      (atomic_t *)(&sem->count)) < 0)
93		rwsem_wake(sem);
94}
95
96/*
97 * implement atomic add functionality
98 */
99static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
100{
101	atomic_add(delta, (atomic_t *)(&sem->count));
102}
103
104/*
105 * downgrade write lock to read lock
106 */
107static inline void __downgrade_write(struct rw_semaphore *sem)
108{
109	int tmp;
110
111	smp_wmb();
112	tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
113	if (tmp < 0)
114		rwsem_downgrade_wake(sem);
115}
116
117static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
118{
119	__down_write(sem);
120}
121
122/*
123 * implement exchange and add functionality
124 */
125static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
126{
127	smp_mb();
128	return atomic_add_return(delta, (atomic_t *)(&sem->count));
129}
130
131#endif /* __KERNEL__ */
132#endif /* _ASM_SH_RWSEM_H */
133