include/asm-ia64/rwsem.h

   1 /*
   2  * asm-ia64/rwsem.h: 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 #include <linux/list.h>
  25 #include <linux/spinlock.h>
  26
  27 #include <asm/intrinsics.h>
  28
  29 /*
  30  * the semaphore definition
  31  */
  32 struct rw_semaphore {
  33         signed long             count;
  34         spinlock_t              wait_lock;
  35         struct list_head        wait_list;
  36 };
  37
  38 #define RWSEM_UNLOCKED_VALUE            __IA64_UL_CONST(0x0000000000000000)
  39 #define RWSEM_ACTIVE_BIAS               __IA64_UL_CONST(0x0000000000000001)
  40 #define RWSEM_ACTIVE_MASK               __IA64_UL_CONST(0x00000000ffffffff)
  41 #define RWSEM_WAITING_BIAS              -__IA64_UL_CONST(0x0000000100000000)
  42 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  43 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  44
  45 #define __RWSEM_INITIALIZER(name) \
  46         { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
  47           LIST_HEAD_INIT((name).wait_list) }
  48
  49 #define DECLARE_RWSEM(name) \
  50         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  51
  52 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  53 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  54 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
  55 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  56
  57 static inline void
  58 init_rwsem (struct rw_semaphore *sem)
  59 {
  60         sem->count = RWSEM_UNLOCKED_VALUE;
  61         spin_lock_init(&sem->wait_lock);
  62         INIT_LIST_HEAD(&sem->wait_list);
  63 }
  64
  65 /*
  66  * lock for reading
  67  */
  68 static inline void
  69 __down_read (struct rw_semaphore *sem)
  70 {
  71         long result = ia64_fetchadd8_acq((unsigned long *)&sem->count, 1);
  72
  73         if (result < 0)
  74                 rwsem_down_read_failed(sem);
  75 }
  76
  77 /*
  78  * lock for writing
  79  */
  80 static inline void
  81 __down_write (struct rw_semaphore *sem)
  82 {
  83         long old, new;
  84
  85         do {
  86                 old = sem->count;
  87                 new = old + RWSEM_ACTIVE_WRITE_BIAS;
  88         } while (cmpxchg_acq(&sem->count, old, new) != old);
  89
  90         if (old != 0)
  91                 rwsem_down_write_failed(sem);
  92 }
  93
  94 /*
  95  * unlock after reading
  96  */
  97 static inline void
  98 __up_read (struct rw_semaphore *sem)
  99 {
 100         long result = ia64_fetchadd8_rel((unsigned long *)&sem->count, -1);
 101
 102         if (result < 0 && (--result & RWSEM_ACTIVE_MASK) == 0)
 103                 rwsem_wake(sem);
 104 }
 105
 106 /*
 107  * unlock after writing
 108  */
 109 static inline void
 110 __up_write (struct rw_semaphore *sem)
 111 {
 112         long old, new;
 113
 114         do {
 115                 old = sem->count;
 116                 new = old - RWSEM_ACTIVE_WRITE_BIAS;
 117         } while (cmpxchg_rel(&sem->count, old, new) != old);
 118
 119         if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0)
 120                 rwsem_wake(sem);
 121 }
 122
 123 /*
 124  * trylock for reading -- returns 1 if successful, 0 if contention
 125  */
 126 static inline int
 127 __down_read_trylock (struct rw_semaphore *sem)
 128 {
 129         long tmp;
 130         while ((tmp = sem->count) >= 0) {
 131                 if (tmp == cmpxchg_acq(&sem->count, tmp, tmp+1)) {
 132                         return 1;
 133                 }
 134         }
 135         return 0;
 136 }
 137
 138 /*
 139  * trylock for writing -- returns 1 if successful, 0 if contention
 140  */
 141 static inline int
 142 __down_write_trylock (struct rw_semaphore *sem)
 143 {
 144         long tmp = cmpxchg_acq(&sem->count, RWSEM_UNLOCKED_VALUE,
 145                               RWSEM_ACTIVE_WRITE_BIAS);
 146         return tmp == RWSEM_UNLOCKED_VALUE;
 147 }
 148
 149 /*
 150  * downgrade write lock to read lock
 151  */
 152 static inline void
 153 __downgrade_write (struct rw_semaphore *sem)
 154 {
 155         long old, new;
 156
 157         do {
 158                 old = sem->count;
 159                 new = old - RWSEM_WAITING_BIAS;
 160         } while (cmpxchg_rel(&sem->count, old, new) != old);
 161
 162         if (old < 0)
 163                 rwsem_downgrade_wake(sem);
 164 }
 165
 166 /*
 167  * Implement atomic add functionality.  These used to be "inline" functions, but GCC v3.1
 168  * doesn't quite optimize this stuff right and ends up with bad calls to fetchandadd.
 169  */
 170 #define rwsem_atomic_add(delta, sem)    atomic64_add(delta, (atomic64_t *)(&(sem)->count))
 171 #define rwsem_atomic_update(delta, sem) atomic64_add_return(delta, (atomic64_t *)(&(sem)->count))
 172
 173 static inline int rwsem_is_locked(struct rw_semaphore *sem)
 174 {
 175         return (sem->count != 0);
 176 }
 177
 178 #endif /* _ASM_IA64_RWSEM_H */