arch/ia64/include/asm/rwsem.h

   1 /*
   2  * R/W semaphores for ia64
   3  *
   4  * Copyright (C) 2003 Ken Chen <kenneth.w.chen@intel.com>
   5  * Copyright (C) 2003 Asit Mallick <asit.k.mallick@intel.com>
   6  * Copyright (C) 2005 Christoph Lameter <clameter@sgi.com>
   7  *
   8  * Based on asm-i386/rwsem.h and other architecture implementation.
   9  *
  10  * The MSW of the count is the negated number of active writers and
  11  * waiting lockers, and the LSW is the total number of active locks.
  12  *
  13  * The lock count is initialized to 0 (no active and no waiting lockers).
  14  *
  15  * When a writer subtracts WRITE_BIAS, it'll get 0xffffffff00000001 for
  16  * the case of an uncontended lock. Readers increment by 1 and see a positive
  17  * value when uncontended, negative if there are writers (and maybe) readers
  18  * waiting (in which case it goes to sleep).
  19  */
  20
  21 #ifndef _ASM_IA64_RWSEM_H
  22 #define _ASM_IA64_RWSEM_H
  23
  24 #ifndef _LINUX_RWSEM_H
  25 #error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
  26 #endif
  27
  28 #include <linux/list.h>
  29 #include <linux/spinlock.h>
  30
  31 #include <asm/intrinsics.h>
  32
  33 /*
  34  * the semaphore definition
  35  */
  36 struct rw_semaphore {
  37         signed long             count;
  38         spinlock_t              wait_lock;
  39         struct list_head        wait_list;
  40 };
  41
  42 #define RWSEM_UNLOCKED_VALUE            __IA64_UL_CONST(0x0000000000000000)
  43 #define RWSEM_ACTIVE_BIAS               (1L)
  44 #define RWSEM_ACTIVE_MASK               (0xffffffffL)
  45 #define RWSEM_WAITING_BIAS              (-0x100000000L)
  46 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  47 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  48
  49 #define __RWSEM_INITIALIZER(name) \
  50         { RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED((name).wait_lock), \
  51           LIST_HEAD_INIT((name).wait_list) }
  52
  53 #define DECLARE_RWSEM(name) \
  54         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  55
  56 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  57 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  58 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
  59 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  60
  61 static inline void
  62 init_rwsem (struct rw_semaphore *sem)
  63 {
  64         sem->count = RWSEM_UNLOCKED_VALUE;
  65         spin_lock_init(&sem->wait_lock);
  66         INIT_LIST_HEAD(&sem->wait_list);
  67 }
  68
  69 /*
  70  * lock for reading
  71  */
  72 static inline void
  73 __down_read (struct rw_semaphore *sem)
  74 {
  75         long result = ia64_fetchadd8_acq((unsigned long *)&sem->count, 1);
  76
  77         if (result < 0)
  78                 rwsem_down_read_failed(sem);
  79 }
  80
  81 /*
  82  * lock for writing
  83  */
  84 static inline void
  85 __down_write (struct rw_semaphore *sem)
  86 {
  87         long old, new;
  88
  89         do {
  90                 old = sem->count;
  91                 new = old + RWSEM_ACTIVE_WRITE_BIAS;
  92         } while (cmpxchg_acq(&sem->count, old, new) != old);
  93
  94         if (old != 0)
  95                 rwsem_down_write_failed(sem);
  96 }
  97
  98 /*
  99  * unlock after reading
 100  */
 101 static inline void
 102 __up_read (struct rw_semaphore *sem)
 103 {
 104         long result = ia64_fetchadd8_rel((unsigned long *)&sem->count, -1);
 105
 106         if (result < 0 && (--result & RWSEM_ACTIVE_MASK) == 0)
 107                 rwsem_wake(sem);
 108 }
 109
 110 /*
 111  * unlock after writing
 112  */
 113 static inline void
 114 __up_write (struct rw_semaphore *sem)
 115 {
 116         long old, new;
 117
 118         do {
 119                 old = sem->count;
 120                 new = old - RWSEM_ACTIVE_WRITE_BIAS;
 121         } while (cmpxchg_rel(&sem->count, old, new) != old);
 122
 123         if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0)
 124                 rwsem_wake(sem);
 125 }
 126
 127 /*
 128  * trylock for reading -- returns 1 if successful, 0 if contention
 129  */
 130 static inline int
 131 __down_read_trylock (struct rw_semaphore *sem)
 132 {
 133         long tmp;
 134         while ((tmp = sem->count) >= 0) {
 135                 if (tmp == cmpxchg_acq(&sem->count, tmp, tmp+1)) {
 136                         return 1;
 137                 }
 138         }
 139         return 0;
 140 }
 141
 142 /*
 143  * trylock for writing -- returns 1 if successful, 0 if contention
 144  */
 145 static inline int
 146 __down_write_trylock (struct rw_semaphore *sem)
 147 {
 148         long tmp = cmpxchg_acq(&sem->count, RWSEM_UNLOCKED_VALUE,
 149                               RWSEM_ACTIVE_WRITE_BIAS);
 150         return tmp == RWSEM_UNLOCKED_VALUE;
 151 }
 152
 153 /*
 154  * downgrade write lock to read lock
 155  */
 156 static inline void
 157 __downgrade_write (struct rw_semaphore *sem)
 158 {
 159         long old, new;
 160
 161         do {
 162                 old = sem->count;
 163                 new = old - RWSEM_WAITING_BIAS;
 164         } while (cmpxchg_rel(&sem->count, old, new) != old);
 165
 166         if (old < 0)
 167                 rwsem_downgrade_wake(sem);
 168 }
 169
 170 /*
 171  * Implement atomic add functionality.  These used to be "inline" functions, but GCC v3.1
 172  * doesn't quite optimize this stuff right and ends up with bad calls to fetchandadd.
 173  */
 174 #define rwsem_atomic_add(delta, sem)    atomic64_add(delta, (atomic64_t *)(&(sem)->count))
 175 #define rwsem_atomic_update(delta, sem) atomic64_add_return(delta, (atomic64_t *)(&(sem)->count))
 176
 177 static inline int rwsem_is_locked(struct rw_semaphore *sem)
 178 {
 179         return (sem->count != 0);
 180 }
 181
 182 #endif /* _ASM_IA64_RWSEM_H */