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39
40
41
42
43
44
45
46 /**
47 * @file
48 *
49 * This file provides reader/writer locks.
50 *
51 * <hr>$Revision: 70030 $<hr>
52 *
53 *
54 */
55
56
57 #ifndef __CVMX_RWLOCK_H__
58 #define __CVMX_RWLOCK_H__
59
60 /* include to get atomic compare and store */
61 #include "cvmx-atomic.h"
62
63 #ifdef __cplusplus
64 extern "C" {
65 #endif
66
67 /* Flags for lock value in rw lock structure */
68 #define CVMX_RWLOCK_WRITE_FLAG 0x1
69 #define CVMX_RWLOCK_READ_INC 0x2
70
71
72 /* Writer preference locks (wp). Can be starved by writers. When a writer
73 * is waiting, no readers are given the lock until all writers are done.
74 */
75 typedef struct
76 {
77 volatile uint32_t lock;
78 volatile uint32_t write_req;
79 volatile uint32_t write_comp;
80 } cvmx_rwlock_wp_lock_t;
81
82 /**
83 * Initialize a reader/writer lock. This must be done
84 * by a single core before used.
85 *
86 * @param lock pointer to rwlock structure
87 */
cvmx_rwlock_wp_init(cvmx_rwlock_wp_lock_t * lock)88 static inline void cvmx_rwlock_wp_init(cvmx_rwlock_wp_lock_t *lock)
89 {
90 lock->lock = 0;
91 lock->write_req = 0;
92 lock->write_comp = 0;
93 }
94
95 /**
96 * Perform a reader lock. If a writer is pending, this
97 * will wait for that writer to complete before locking.
98 *
99 * NOTE: Each thread/process must only lock any rwlock
100 * once, or else a deadlock may result.
101 *
102 * @param lock pointer to rwlock structure
103 */
cvmx_rwlock_wp_read_lock(cvmx_rwlock_wp_lock_t * lock)104 static inline void cvmx_rwlock_wp_read_lock(cvmx_rwlock_wp_lock_t *lock)
105 {
106
107 /* Wait for outstanding write requests to be serviced */
108 while (lock->write_req != lock->write_comp)
109 ;
110 /* Add ourselves to interested reader count */
111 cvmx_atomic_add32_nosync((int32_t *)&(lock->lock), CVMX_RWLOCK_READ_INC);
112 /* Wait for writer to finish. No writer will start again
113 ** until after we are done since we have already incremented
114 ** the reader count
115 */
116 while (lock->lock & CVMX_RWLOCK_WRITE_FLAG)
117 ;
118
119 }
120
121 /**
122 * Perform a reader unlock.
123 *
124 * @param lock pointer to rwlock structure
125 */
cvmx_rwlock_wp_read_unlock(cvmx_rwlock_wp_lock_t * lock)126 static inline void cvmx_rwlock_wp_read_unlock(cvmx_rwlock_wp_lock_t *lock)
127 {
128 /* Remove ourselves to reader count */
129 cvmx_atomic_add32_nosync((int32_t *)&(lock->lock), -CVMX_RWLOCK_READ_INC);
130 }
131
132 /**
133 * Perform a writer lock. Any readers that attempt
134 * to get a lock while there are any pending write locks
135 * will wait until all writers have completed. Starvation
136 * of readers by writers is possible and must be avoided
137 * by the application.
138 *
139 * @param lock pointer to rwlock structure
140 */
cvmx_rwlock_wp_write_lock(cvmx_rwlock_wp_lock_t * lock)141 static inline void cvmx_rwlock_wp_write_lock(cvmx_rwlock_wp_lock_t *lock)
142 {
143 /* Get previous value of write requests */
144 uint32_t prev_writers = ((uint32_t)cvmx_atomic_fetch_and_add32((int32_t *)&(lock->write_req), 1));
145 /* Spin until our turn */
146 while (prev_writers != lock->write_comp)
147 ;
148 /* Spin until no other readers or writers, then set write flag */
149 while (!cvmx_atomic_compare_and_store32((uint32_t *)&(lock->lock), 0, CVMX_RWLOCK_WRITE_FLAG))
150 ;
151
152 }
153 /**
154 * Perform a writer unlock.
155 *
156 * @param lock pointer to rwlock structure
157 */
cvmx_rwlock_wp_write_unlock(cvmx_rwlock_wp_lock_t * lock)158 static inline void cvmx_rwlock_wp_write_unlock(cvmx_rwlock_wp_lock_t *lock)
159 {
160 /* Remove our writer flag */
161 CVMX_SYNCWS; /* Make sure all writes in protected region are visible before unlock */
162 cvmx_atomic_add32_nosync((int32_t *)&(lock->lock), -CVMX_RWLOCK_WRITE_FLAG);
163 cvmx_atomic_add32_nosync((int32_t *)&(lock->write_comp), 1);
164 CVMX_SYNCWS; /* push unlock writes out, but don't stall */
165 }
166
167 #ifdef __cplusplus
168 }
169 #endif
170
171 #endif /* __CVMX_RWLOCK_H__ */
172