LXR linux/arch/powerpc/include/asm/rwsem.h

   1#ifndef _ASM_POWERPC_RWSEM_H
   2#define _ASM_POWERPC_RWSEM_H
   3
   4#ifndef _LINUX_RWSEM_H
   5#error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
   6#endif
   7
   8#ifdef __KERNEL__
   9
  10/*
  11 * R/W semaphores for PPC using the stuff in lib/rwsem.c.
  12 * Adapted largely from include/asm-i386/rwsem.h
  13 * by Paul Mackerras <paulus@samba.org>.
  14 */
  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 */
  24#ifdef CONFIG_PPC64
  25# define RWSEM_ACTIVE_MASK              0xffffffffL
  26#else
  27# define RWSEM_ACTIVE_MASK              0x0000ffffL
  28#endif
  29
  30#define RWSEM_UNLOCKED_VALUE            0x00000000L
  31#define RWSEM_ACTIVE_BIAS               0x00000001L
  32#define RWSEM_WAITING_BIAS              (-RWSEM_ACTIVE_MASK-1)
  33#define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  34#define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  35
  36struct rw_semaphore {
  37        long                    count;
  38        spinlock_t              wait_lock;
  39        struct list_head        wait_list;
  40#ifdef CONFIG_DEBUG_LOCK_ALLOC
  41        struct lockdep_map      dep_map;
  42#endif
  43};
  44
  45#ifdef CONFIG_DEBUG_LOCK_ALLOC
  46# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
  47#else
  48# define __RWSEM_DEP_MAP_INIT(lockname)
  49#endif
  50
  51#define __RWSEM_INITIALIZER(name)                               \
  52{                                                               \
  53        RWSEM_UNLOCKED_VALUE,                                   \
  54        __SPIN_LOCK_UNLOCKED((name).wait_lock),                 \
  55        LIST_HEAD_INIT((name).wait_list)                        \
  56        __RWSEM_DEP_MAP_INIT(name)                              \
  57}
  58
  59#define DECLARE_RWSEM(name)             \
  60        struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  61
  62extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  63extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  64extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
  65extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  66
  67extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
  68                         struct lock_class_key *key);
  69
  70#define init_rwsem(sem)                                 \
  71        do {                                            \
  72                static struct lock_class_key __key;     \
  73                                                        \
  74                __init_rwsem((sem), #sem, &__key);      \
  75        } while (0)
  76
  77/*
  78 * lock for reading
  79 */
  80static inline void __down_read(struct rw_semaphore *sem)
  81{
  82        if (unlikely(atomic_long_inc_return((atomic_long_t *)&sem->count) <= 0))
  83                rwsem_down_read_failed(sem);
  84}
  85
  86static inline int __down_read_trylock(struct rw_semaphore *sem)
  87{
  88        long tmp;
  89
  90        while ((tmp = sem->count) >= 0) {
  91                if (tmp == cmpxchg(&sem->count, tmp,
  92                                   tmp + RWSEM_ACTIVE_READ_BIAS)) {
  93                        return 1;
  94                }
  95        }
  96        return 0;
  97}
  98
  99/*
 100 * lock for writing
 101 */
 102static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
 103{
 104        long tmp;
 105
 106        tmp = atomic_long_add_return(RWSEM_ACTIVE_WRITE_BIAS,
 107                                     (atomic_long_t *)&sem->count);
 108        if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
 109                rwsem_down_write_failed(sem);
 110}
 111
 112static inline void __down_write(struct rw_semaphore *sem)
 113{
 114        __down_write_nested(sem, 0);
 115}
 116
 117static inline int __down_write_trylock(struct rw_semaphore *sem)
 118{
 119        long tmp;
 120
 121        tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
 122                      RWSEM_ACTIVE_WRITE_BIAS);
 123        return tmp == RWSEM_UNLOCKED_VALUE;
 124}
 125
 126/*
 127 * unlock after reading
 128 */
 129static inline void __up_read(struct rw_semaphore *sem)
 130{
 131        long tmp;
 132
 133        tmp = atomic_long_dec_return((atomic_long_t *)&sem->count);
 134        if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
 135                rwsem_wake(sem);
 136}
 137
 138/*
 139 * unlock after writing
 140 */
 141static inline void __up_write(struct rw_semaphore *sem)
 142{
 143        if (unlikely(atomic_long_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
 144                                 (atomic_long_t *)&sem->count) < 0))
 145                rwsem_wake(sem);
 146}
 147
 148/*
 149 * implement atomic add functionality
 150 */
 151static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)
 152{
 153        atomic_long_add(delta, (atomic_long_t *)&sem->count);
 154}
 155
 156/*
 157 * downgrade write lock to read lock
 158 */
 159static inline void __downgrade_write(struct rw_semaphore *sem)
 160{
 161        long tmp;
 162
 163        tmp = atomic_long_add_return(-RWSEM_WAITING_BIAS,
 164                                     (atomic_long_t *)&sem->count);
 165        if (tmp < 0)
 166                rwsem_downgrade_wake(sem);
 167}
 168
 169/*
 170 * implement exchange and add functionality
 171 */
 172static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
 173{
 174        return atomic_long_add_return(delta, (atomic_long_t *)&sem->count);
 175}
 176
 177static inline int rwsem_is_locked(struct rw_semaphore *sem)
 178{
 179        return sem->count != 0;
 180}
 181
 182#endif  /* __KERNEL__ */
 183#endif  /* _ASM_POWERPC_RWSEM_H */
 184