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rwsem.h
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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  */
30 static 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
36 }
37 
38 static 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  */
55 static inline void __down_write(struct rw_semaphore *sem)
56 {
57  int tmp;
58 
60  (atomic_t *)(&sem->count));
61  if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
62  smp_wmb();
63  else
65 }
66 
67 static inline int __down_write_trylock(struct rw_semaphore *sem)
68 {
69  int tmp;
70 
71  tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
73  smp_wmb();
74  return tmp == RWSEM_UNLOCKED_VALUE;
75 }
76 
77 /*
78  * unlock after reading
79  */
80 static 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  */
93 static inline void __up_write(struct rw_semaphore *sem)
94 {
95  smp_wmb();
97  (atomic_t *)(&sem->count)) < 0)
98  rwsem_wake(sem);
99 }
100 
101 /*
102  * implement atomic add functionality
103  */
104 static 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  */
112 static inline void __downgrade_write(struct rw_semaphore *sem)
113 {
114  int tmp;
115 
116  smp_wmb();
118  if (tmp < 0)
120 }
121 
122 /*
123  * implement exchange and add functionality
124  */
125 static 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 */