include/asm-mips64/semaphore.h

   1 /*
   2  * License.  See the file "COPYING" in the main directory of this archive
   3  * for more details.
   4  *
   5  * Copyright (C) 1996  Linus Torvalds
   6  * Copyright (C) 1998, 1999, 2000  Ralf Baechle
   7  * Copyright (C) 1999, 2000  Silicon Graphics, Inc.
   8  */
   9 #ifndef _ASM_SEMAPHORE_H
  10 #define _ASM_SEMAPHORE_H
  11
  12 #include <asm/system.h>
  13 #include <asm/atomic.h>
  14 #include <linux/spinlock.h>
  15 #include <linux/wait.h>
  16
  17 struct semaphore {
  18 #ifdef __MIPSEB__
  19         atomic_t count;
  20         atomic_t waking;
  21 #else
  22         atomic_t waking;
  23         atomic_t count;
  24 #endif
  25         wait_queue_head_t wait;
  26 #if WAITQUEUE_DEBUG
  27         long __magic;
  28 #endif
  29 };
  30
  31 #if WAITQUEUE_DEBUG
  32 # define __SEM_DEBUG_INIT(name) \
  33                 , (long)&(name).__magic
  34 #else
  35 # define __SEM_DEBUG_INIT(name)
  36 #endif
  37
  38 #ifdef __MIPSEB__
  39 #define __SEMAPHORE_INITIALIZER(name,count) \
  40 { ATOMIC_INIT(count), ATOMIC_INIT(0), __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
  41         __SEM_DEBUG_INIT(name) }
  42 #else
  43 #define __SEMAPHORE_INITIALIZER(name,count) \
  44 { ATOMIC_INIT(0), ATOMIC_INIT(count), __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
  45         __SEM_DEBUG_INIT(name) }
  46 #endif
  47
  48 #define __MUTEX_INITIALIZER(name) \
  49         __SEMAPHORE_INITIALIZER(name,1)
  50
  51 #define __DECLARE_SEMAPHORE_GENERIC(name,count) \
  52         struct semaphore name = __SEMAPHORE_INITIALIZER(name,count)
  53
  54 #define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1)
  55 #define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0)
  56
  57 static inline void sema_init (struct semaphore *sem, int val)
  58 {
  59         atomic_set(&sem->count, val);
  60         atomic_set(&sem->waking, 0);
  61         init_waitqueue_head(&sem->wait);
  62 #if WAITQUEUE_DEBUG
  63         sem->__magic = (long)&sem->__magic;
  64 #endif
  65 }
  66
  67 static inline void init_MUTEX (struct semaphore *sem)
  68 {
  69         sema_init(sem, 1);
  70 }
  71
  72 static inline void init_MUTEX_LOCKED (struct semaphore *sem)
  73 {
  74         sema_init(sem, 0);
  75 }
  76
  77 asmlinkage void __down(struct semaphore * sem);
  78 asmlinkage int  __down_interruptible(struct semaphore * sem);
  79 asmlinkage int __down_trylock(struct semaphore * sem);
  80 asmlinkage void __up(struct semaphore * sem);
  81
  82 static inline void down(struct semaphore * sem)
  83 {
  84 #if WAITQUEUE_DEBUG
  85         CHECK_MAGIC(sem->__magic);
  86 #endif
  87         if (atomic_dec_return(&sem->count) < 0)
  88                 __down(sem);
  89 }
  90
  91 static inline int down_interruptible(struct semaphore * sem)
  92 {
  93         int ret = 0;
  94
  95 #if WAITQUEUE_DEBUG
  96         CHECK_MAGIC(sem->__magic);
  97 #endif
  98         if (atomic_dec_return(&sem->count) < 0)
  99                 ret = __down_interruptible(sem);
 100         return ret;
 101 }
 102
 103 /*
 104  * down_trylock returns 0 on success, 1 if we failed to get the lock.
 105  *
 106  * We must manipulate count and waking simultaneously and atomically.
 107  * Here, we this by using ll/sc on the pair of 32-bit words.
 108  *
 109  * Pseudocode:
 110  *
 111  *   Decrement(sem->count)
 112  *   If(sem->count >=0) {
 113  *      Return(SUCCESS)                 // resource is free
 114  *   } else {
 115  *      If(sem->waking <= 0) {          // if no wakeup pending
 116  *         Increment(sem->count)        // undo decrement
 117  *         Return(FAILURE)
 118  *      } else {
 119  *         Decrement(sem->waking)       // otherwise "steal" wakeup
 120  *         Return(SUCCESS)
 121  *      }
 122  *   }
 123  */
 124 static inline int down_trylock(struct semaphore * sem)
 125 {
 126         long ret, tmp, tmp2, sub;
 127
 128 #if WAITQUEUE_DEBUG
 129         CHECK_MAGIC(sem->__magic);
 130 #endif
 131
 132         __asm__ __volatile__("
 133                         .set    mips3
 134
 135                 0:      lld     %1, %4
 136                         dli     %3, 0x0000000100000000
 137                         dsubu   %1, %3
 138                         li      %0, 0
 139                         bgez    %1, 2f
 140                         sll     %2, %1, 0
 141                         blez    %2, 1f
 142                         daddiu  %1, %1, -1
 143                         b       2f
 144                 1:
 145                         daddu   %1, %1, %3
 146                         li      %0, 1
 147                 2:
 148                         scd     %1, %4
 149                         beqz    %1, 0b
 150
 151                         .set    mips0"
 152                 : "=&r"(ret), "=&r"(tmp), "=&r"(tmp2), "=&r"(sub)
 153                 : "m"(*sem)
 154                 : "memory");
 155
 156         return ret;
 157 }
 158
 159 /*
 160  * Note! This is subtle. We jump to wake people up only if
 161  * the semaphore was negative (== somebody was waiting on it).
 162  */
 163 static inline void up(struct semaphore * sem)
 164 {
 165 #if WAITQUEUE_DEBUG
 166         CHECK_MAGIC(sem->__magic);
 167 #endif
 168         if (atomic_inc_return(&sem->count) <= 0)
 169                 __up(sem);
 170 }
 171
 172 /*
 173  * rw mutexes (should that be mutices? =) -- throw rw spinlocks and
 174  * semaphores together, and this is what we end up with...
 175  *
 176  * The lock is initialized to BIAS.  This way, a writer subtracts BIAS ands
 177  * gets 0 for the case of an uncontended lock.  Readers decrement by 1 and
 178  * see a positive value when uncontended, negative if there are writers
 179  * waiting (in which case it goes to sleep).
 180  *
 181  * The value 0x01000000 supports up to 128 processors and lots of processes.
 182  * BIAS must be chosen such that subtracting BIAS once per CPU will result
 183  * in the int remaining negative.  In terms of fairness, this should result
 184  * in the lock flopping back and forth between readers and writers under
 185  * heavy use.
 186  *
 187  * Once we start supporting machines with more than 128 CPUs, we should go
 188  * for using a 64bit atomic type instead of 32bit as counter. We shall
 189  * probably go for bias 0x80000000 then, so that single sethi can set it.
 190  * */
 191
 192 #define RW_LOCK_BIAS            0x01000000
 193
 194 struct rw_semaphore {
 195         atomic_t                count;
 196         /* bit 0 means read bias granted;
 197            bit 1 means write bias granted.  */
 198         unsigned long           granted;
 199         wait_queue_head_t       wait;
 200         wait_queue_head_t       write_bias_wait;
 201 #if WAITQUEUE_DEBUG
 202         long                    __magic;
 203         atomic_t                readers;
 204         atomic_t                writers;
 205 #endif
 206 };
 207
 208 #if WAITQUEUE_DEBUG
 209 #define __RWSEM_DEBUG_INIT      , ATOMIC_INIT(0), ATOMIC_INIT(0)
 210 #else
 211 #define __RWSEM_DEBUG_INIT      /* */
 212 #endif
 213
 214 #define __RWSEM_INITIALIZER(name,count)                                 \
 215         { ATOMIC_INIT(count), 0,                                        \
 216           __WAIT_QUEUE_HEAD_INITIALIZER((name).wait),                   \
 217           __WAIT_QUEUE_HEAD_INITIALIZER((name).write_bias_wait)         \
 218           __SEM_DEBUG_INIT(name) __RWSEM_DEBUG_INIT }
 219
 220 #define __DECLARE_RWSEM_GENERIC(name,count) \
 221         struct rw_semaphore name = __RWSEM_INITIALIZER(name,count)
 222
 223 #define DECLARE_RWSEM(name) \
 224         __DECLARE_RWSEM_GENERIC(name, RW_LOCK_BIAS)
 225 #define DECLARE_RWSEM_READ_LOCKED(name) \
 226         __DECLARE_RWSEM_GENERIC(name, RW_LOCK_BIAS-1)
 227 #define DECLARE_RWSEM_WRITE_LOCKED(name) \
 228         __DECLARE_RWSEM_GENERIC(name, 0)
 229
 230 static inline void init_rwsem(struct rw_semaphore *sem)
 231 {
 232         atomic_set(&sem->count, RW_LOCK_BIAS);
 233         sem->granted = 0;
 234         init_waitqueue_head(&sem->wait);
 235         init_waitqueue_head(&sem->write_bias_wait);
 236 #if WAITQUEUE_DEBUG
 237         sem->__magic = (long)&sem->__magic;
 238         atomic_set(&sem->readers, 0);
 239         atomic_set(&sem->writers, 0);
 240 #endif
 241 }
 242
 243 /* The expensive part is outlined.  */
 244 extern void __down_read(struct rw_semaphore *sem, int count);
 245 extern void __down_write(struct rw_semaphore *sem, int count);
 246 extern void __rwsem_wake(struct rw_semaphore *sem, unsigned long readers);
 247
 248 static inline void down_read(struct rw_semaphore *sem)
 249 {
 250         int count;
 251
 252 #if WAITQUEUE_DEBUG
 253         CHECK_MAGIC(sem->__magic);
 254 #endif
 255
 256         count = atomic_dec_return(&sem->count);
 257         if (count < 0) {
 258                 __down_read(sem, count);
 259         }
 260         mb();
 261
 262 #if WAITQUEUE_DEBUG
 263         if (sem->granted & 2)
 264                 BUG();
 265         if (atomic_read(&sem->writers))
 266                 BUG();
 267         atomic_inc(&sem->readers);
 268 #endif
 269 }
 270
 271 static inline void down_write(struct rw_semaphore *sem)
 272 {
 273         int count;
 274
 275 #if WAITQUEUE_DEBUG
 276         CHECK_MAGIC(sem->__magic);
 277 #endif
 278
 279         count = atomic_sub_return(RW_LOCK_BIAS, &sem->count);
 280         if (count) {
 281                 __down_write(sem, count);
 282         }
 283         mb();
 284
 285 #if WAITQUEUE_DEBUG
 286         if (atomic_read(&sem->writers))
 287                 BUG();
 288         if (atomic_read(&sem->readers))
 289                 BUG();
 290         if (sem->granted & 3)
 291                 BUG();
 292         atomic_inc(&sem->writers);
 293 #endif
 294 }
 295
 296 /* When a reader does a release, the only significant case is when
 297    there was a writer waiting, and we've bumped the count to 0: we must
 298    wake the writer up.  */
 299
 300 static inline void up_read(struct rw_semaphore *sem)
 301 {
 302         int count;
 303
 304 #if WAITQUEUE_DEBUG
 305         CHECK_MAGIC(sem->__magic);
 306         if (sem->granted & 2)
 307                 BUG();
 308         if (atomic_read(&sem->writers))
 309                 BUG();
 310         atomic_dec(&sem->readers);
 311 #endif
 312
 313         mb();
 314         count = atomic_inc_return(&sem->count);
 315         if (count == 0) {
 316                 __rwsem_wake(sem, 0);
 317         }
 318 }
 319
 320 /*
 321  * Releasing the writer is easy -- just release it and wake up any sleepers.
 322  */
 323 static inline void up_write(struct rw_semaphore *sem)
 324 {
 325         int count;
 326
 327 #if WAITQUEUE_DEBUG
 328         CHECK_MAGIC(sem->__magic);
 329         if (sem->granted & 3)
 330                 BUG();
 331         if (atomic_read(&sem->readers))
 332                 BUG();
 333         if (atomic_read(&sem->writers) != 1)
 334                 BUG();
 335         atomic_dec(&sem->writers);
 336 #endif
 337
 338         mb();
 339         count = atomic_add_return(RW_LOCK_BIAS, &sem->count);
 340         if (count - RW_LOCK_BIAS < 0 && count >= 0) {
 341                 /* Only do the wake if we're no longer negative.  */
 342                 __rwsem_wake(sem, count);
 343         }
 344 }
 345
 346 #endif /* _ASM_SEMAPHORE_H */