1/*
2 * include/asm-xtensa/rwsem.h
3 *
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
6 * for more details.
7 *
8 * Largely copied from include/asm-ppc/rwsem.h
9 *
10 * Copyright (C) 2001 - 2005 Tensilica Inc.
11 */
12
13#ifndef _XTENSA_RWSEM_H
14#define _XTENSA_RWSEM_H
15
16#ifndef _LINUX_RWSEM_H
17#error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
18#endif
19
20#define RWSEM_UNLOCKED_VALUE		0x00000000
21#define RWSEM_ACTIVE_BIAS		0x00000001
22#define RWSEM_ACTIVE_MASK		0x0000ffff
23#define RWSEM_WAITING_BIAS		(-0x00010000)
24#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
25#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
26
27/*
28 * lock for reading
29 */
30static inline void __down_read(struct rw_semaphore *sem)
31{
32	if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0)
33		smp_wmb();
34	else
35		rwsem_down_read_failed(sem);
36}
37
38static inline int __down_read_trylock(struct rw_semaphore *sem)
39{
40	int tmp;
41
42	while ((tmp = sem->count) >= 0) {
43		if (tmp == cmpxchg(&sem->count, tmp,
44				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
45			smp_wmb();
46			return 1;
47		}
48	}
49	return 0;
50}
51
52/*
53 * lock for writing
54 */
55static inline void __down_write(struct rw_semaphore *sem)
56{
57	int tmp;
58
59	tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
60				(atomic_t *)(&sem->count));
61	if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
62		smp_wmb();
63	else
64		rwsem_down_write_failed(sem);
65}
66
67static inline int __down_write_trylock(struct rw_semaphore *sem)
68{
69	int tmp;
70
71	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
72		      RWSEM_ACTIVE_WRITE_BIAS);
73	smp_wmb();
74	return tmp == RWSEM_UNLOCKED_VALUE;
75}
76
77/*
78 * unlock after reading
79 */
80static inline void __up_read(struct rw_semaphore *sem)
81{
82	int tmp;
83
84	smp_wmb();
85	tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
86	if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
87		rwsem_wake(sem);
88}
89
90/*
91 * unlock after writing
92 */
93static inline void __up_write(struct rw_semaphore *sem)
94{
95	smp_wmb();
96	if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
97			      (atomic_t *)(&sem->count)) < 0)
98		rwsem_wake(sem);
99}
100
101/*
102 * implement atomic add functionality
103 */
104static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
105{
106	atomic_add(delta, (atomic_t *)(&sem->count));
107}
108
109/*
110 * downgrade write lock to read lock
111 */
112static inline void __downgrade_write(struct rw_semaphore *sem)
113{
114	int tmp;
115
116	smp_wmb();
117	tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
118	if (tmp < 0)
119		rwsem_downgrade_wake(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	/* _XTENSA_RWSEM_H */
132