/arch/xtensa/include/asm/rwsem.h

  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#include <linux/list.h>
 21#include <linux/spinlock.h>
 22#include <asm/atomic.h>
 23#include <asm/system.h>
 24
 25/*
 26 * the semaphore definition
 27 */
 28struct rw_semaphore {
 29	signed long		count;
 30#define RWSEM_UNLOCKED_VALUE		0x00000000
 31#define RWSEM_ACTIVE_BIAS		0x00000001
 32#define RWSEM_ACTIVE_MASK		0x0000ffff
 33#define RWSEM_WAITING_BIAS		(-0x00010000)
 34#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
 35#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
 36	spinlock_t		wait_lock;
 37	struct list_head	wait_list;
 38};
 39
 40#define __RWSEM_INITIALIZER(name) \
 41	{ RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
 42	  LIST_HEAD_INIT((name).wait_list) }
 43
 44#define DECLARE_RWSEM(name)		\
 45	struct rw_semaphore name = __RWSEM_INITIALIZER(name)
 46
 47extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
 48extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
 49extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
 50extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
 51
 52static inline void init_rwsem(struct rw_semaphore *sem)
 53{
 54	sem->count = RWSEM_UNLOCKED_VALUE;
 55	spin_lock_init(&sem->wait_lock);
 56	INIT_LIST_HEAD(&sem->wait_list);
 57}
 58
 59/*
 60 * lock for reading
 61 */
 62static inline void __down_read(struct rw_semaphore *sem)
 63{
 64	if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0)
 65		smp_wmb();
 66	else
 67		rwsem_down_read_failed(sem);
 68}
 69
 70static inline int __down_read_trylock(struct rw_semaphore *sem)
 71{
 72	int tmp;
 73
 74	while ((tmp = sem->count) >= 0) {
 75		if (tmp == cmpxchg(&sem->count, tmp,
 76				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
 77			smp_wmb();
 78			return 1;
 79		}
 80	}
 81	return 0;
 82}
 83
 84/*
 85 * lock for writing
 86 */
 87static inline void __down_write(struct rw_semaphore *sem)
 88{
 89	int tmp;
 90
 91	tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
 92				(atomic_t *)(&sem->count));
 93	if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
 94		smp_wmb();
 95	else
 96		rwsem_down_write_failed(sem);
 97}
 98
 99static inline int __down_write_trylock(struct rw_semaphore *sem)
100{
101	int tmp;
102
103	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
104		      RWSEM_ACTIVE_WRITE_BIAS);
105	smp_wmb();
106	return tmp == RWSEM_UNLOCKED_VALUE;
107}
108
109/*
110 * unlock after reading
111 */
112static inline void __up_read(struct rw_semaphore *sem)
113{
114	int tmp;
115
116	smp_wmb();
117	tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
118	if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
119		rwsem_wake(sem);
120}
121
122/*
123 * unlock after writing
124 */
125static inline void __up_write(struct rw_semaphore *sem)
126{
127	smp_wmb();
128	if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
129			      (atomic_t *)(&sem->count)) < 0)
130		rwsem_wake(sem);
131}
132
133/*
134 * implement atomic add functionality
135 */
136static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
137{
138	atomic_add(delta, (atomic_t *)(&sem->count));
139}
140
141/*
142 * downgrade write lock to read lock
143 */
144static inline void __downgrade_write(struct rw_semaphore *sem)
145{
146	int tmp;
147
148	smp_wmb();
149	tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
150	if (tmp < 0)
151		rwsem_downgrade_wake(sem);
152}
153
154/*
155 * implement exchange and add functionality
156 */
157static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
158{
159	smp_mb();
160	return atomic_add_return(delta, (atomic_t *)(&sem->count));
161}
162
163static inline int rwsem_is_locked(struct rw_semaphore *sem)
164{
165	return (sem->count != 0);
166}
167
168#endif	/* _XTENSA_RWSEM_H */