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#include <linux/list.h> 17#include <linux/spinlock.h> 18#include <asm/atomic.h> 19#include <asm/system.h> 20 21/* 22 * the semaphore definition 23 */ 24struct rw_semaphore { 25 signed long count; 26#define RWSEM_UNLOCKED_VALUE 0x00000000 27#define RWSEM_ACTIVE_BIAS 0x00000001 28#define RWSEM_ACTIVE_MASK 0x0000ffff 29#define RWSEM_WAITING_BIAS (-0x00010000) 30#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS 31#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS) 32 spinlock_t wait_lock; 33 struct list_head wait_list; 34}; 35 36#define __RWSEM_INITIALIZER(name) \ 37 { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \ 38 LIST_HEAD_INIT((name).wait_list) } 39 40#define DECLARE_RWSEM(name) \ 41 struct rw_semaphore name = __RWSEM_INITIALIZER(name) 42 43extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem); 44extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem); 45extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem); 46extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem); 47 48static inline void init_rwsem(struct rw_semaphore *sem) 49{ 50 sem->count = RWSEM_UNLOCKED_VALUE; 51 spin_lock_init(&sem->wait_lock); 52 INIT_LIST_HEAD(&sem->wait_list); 53} 54 55/* 56 * lock for reading 57 */ 58static inline void __down_read(struct rw_semaphore *sem) 59{ 60 if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0) 61 smp_wmb(); 62 else 63 rwsem_down_read_failed(sem); 64} 65 66static inline int __down_read_trylock(struct rw_semaphore *sem) 67{ 68 int tmp; 69 70 while ((tmp = sem->count) >= 0) { 71 if (tmp == cmpxchg(&sem->count, tmp, 72 tmp + RWSEM_ACTIVE_READ_BIAS)) { 73 smp_wmb(); 74 return 1; 75 } 76 } 77 return 0; 78} 79 80/* 81 * lock for writing 82 */ 83static inline void __down_write(struct rw_semaphore *sem) 84{ 85 int tmp; 86 87 tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS, 88 (atomic_t *)(&sem->count)); 89 if (tmp == RWSEM_ACTIVE_WRITE_BIAS) 90 smp_wmb(); 91 else 92 rwsem_down_write_failed(sem); 93} 94 95static inline int __down_write_trylock(struct rw_semaphore *sem) 96{ 97 int tmp; 98 99 tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE, 100 RWSEM_ACTIVE_WRITE_BIAS); 101 smp_wmb(); 102 return tmp == RWSEM_UNLOCKED_VALUE; 103} 104 105/* 106 * unlock after reading 107 */ 108static inline void __up_read(struct rw_semaphore *sem) 109{ 110 int tmp; 111 112 smp_wmb(); 113 tmp = atomic_sub_return(1,(atomic_t *)(&sem->count)); 114 if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0) 115 rwsem_wake(sem); 116} 117 118/* 119 * unlock after writing 120 */ 121static inline void __up_write(struct rw_semaphore *sem) 122{ 123 smp_wmb(); 124 if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS, 125 (atomic_t *)(&sem->count)) < 0) 126 rwsem_wake(sem); 127} 128 129/* 130 * implement atomic add functionality 131 */ 132static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem) 133{ 134 atomic_add(delta, (atomic_t *)(&sem->count)); 135} 136 137/* 138 * downgrade write lock to read lock 139 */ 140static inline void __downgrade_write(struct rw_semaphore *sem) 141{ 142 int tmp; 143 144 smp_wmb(); 145 tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count)); 146 if (tmp < 0) 147 rwsem_downgrade_wake(sem); 148} 149 150/* 151 * implement exchange and add functionality 152 */ 153static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem) 154{ 155 smp_mb(); 156 return atomic_add_return(delta, (atomic_t *)(&sem->count)); 157} 158 159static inline int rwsem_is_locked(struct rw_semaphore *sem) 160{ 161 return (sem->count != 0); 162} 163 164#endif /* _XTENSA_RWSEM_H */ 165