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
  36 struct 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
  62 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  63 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  64 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
  65 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  66
  67 extern 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  */
  80 static 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
  86 static 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  */
 102 static 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
 112 static inline void __down_write(struct rw_semaphore *sem)
 113 {
 114         __down_write_nested(sem, 0);
 115 }
 116
 117 static 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  */
 129 static 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  */
 141 static 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  */
 151 static 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  */
 159 static 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  */
 172 static 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
 177 static 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 */