arch/arc/include/asm/spinlock.h

   1 /*
   2  * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  */
   8
   9 #ifndef __ASM_SPINLOCK_H
  10 #define __ASM_SPINLOCK_H
  11
  12 #include <asm/spinlock_types.h>
  13 #include <asm/processor.h>
  14 #include <asm/barrier.h>
  15
  16 #define arch_spin_is_locked(x)  ((x)->slock != __ARCH_SPIN_LOCK_UNLOCKED__)
  17 #define arch_spin_lock_flags(lock, flags)       arch_spin_lock(lock)
  18
  19 #ifdef CONFIG_ARC_HAS_LLSC
  20
  21 static inline void arch_spin_lock(arch_spinlock_t *lock)
  22 {
  23         unsigned int val;
  24
  25         smp_mb();
  26
  27         __asm__ __volatile__(
  28         "1:     llock   %[val], [%[slock]]      \n"
  29         "       breq    %[val], %[LOCKED], 1b   \n"     /* spin while LOCKED */
  30         "       scond   %[LOCKED], [%[slock]]   \n"     /* acquire */
  31         "       bnz     1b                      \n"
  32         "                                       \n"
  33         : [val]         "=&r"   (val)
  34         : [slock]       "r"     (&(lock->slock)),
  35           [LOCKED]      "r"     (__ARCH_SPIN_LOCK_LOCKED__)
  36         : "memory", "cc");
  37
  38         smp_mb();
  39 }
  40
  41 /* 1 - lock taken successfully */
  42 static inline int arch_spin_trylock(arch_spinlock_t *lock)
  43 {
  44         unsigned int val, got_it = 0;
  45
  46         smp_mb();
  47
  48         __asm__ __volatile__(
  49         "1:     llock   %[val], [%[slock]]      \n"
  50         "       breq    %[val], %[LOCKED], 4f   \n"     /* already LOCKED, just bail */
  51         "       scond   %[LOCKED], [%[slock]]   \n"     /* acquire */
  52         "       bnz     1b                      \n"
  53         "       mov     %[got_it], 1            \n"
  54         "4:                                     \n"
  55         "                                       \n"
  56         : [val]         "=&r"   (val),
  57           [got_it]      "+&r"   (got_it)
  58         : [slock]       "r"     (&(lock->slock)),
  59           [LOCKED]      "r"     (__ARCH_SPIN_LOCK_LOCKED__)
  60         : "memory", "cc");
  61
  62         smp_mb();
  63
  64         return got_it;
  65 }
  66
  67 static inline void arch_spin_unlock(arch_spinlock_t *lock)
  68 {
  69         smp_mb();
  70
  71         lock->slock = __ARCH_SPIN_LOCK_UNLOCKED__;
  72
  73         smp_mb();
  74 }
  75
  76 /*
  77  * Read-write spinlocks, allowing multiple readers but only one writer.
  78  * Unfair locking as Writers could be starved indefinitely by Reader(s)
  79  */
  80
  81 static inline void arch_read_lock(arch_rwlock_t *rw)
  82 {
  83         unsigned int val;
  84
  85         smp_mb();
  86
  87         /*
  88          * zero means writer holds the lock exclusively, deny Reader.
  89          * Otherwise grant lock to first/subseq reader
  90          *
  91          *      if (rw->counter > 0) {
  92          *              rw->counter--;
  93          *              ret = 1;
  94          *      }
  95          */
  96
  97         __asm__ __volatile__(
  98         "1:     llock   %[val], [%[rwlock]]     \n"
  99         "       brls    %[val], %[WR_LOCKED], 1b\n"     /* <= 0: spin while write locked */
 100         "       sub     %[val], %[val], 1       \n"     /* reader lock */
 101         "       scond   %[val], [%[rwlock]]     \n"
 102         "       bnz     1b                      \n"
 103         "                                       \n"
 104         : [val]         "=&r"   (val)
 105         : [rwlock]      "r"     (&(rw->counter)),
 106           [WR_LOCKED]   "ir"    (0)
 107         : "memory", "cc");
 108
 109         smp_mb();
 110 }
 111
 112 /* 1 - lock taken successfully */
 113 static inline int arch_read_trylock(arch_rwlock_t *rw)
 114 {
 115         unsigned int val, got_it = 0;
 116
 117         smp_mb();
 118
 119         __asm__ __volatile__(
 120         "1:     llock   %[val], [%[rwlock]]     \n"
 121         "       brls    %[val], %[WR_LOCKED], 4f\n"     /* <= 0: already write locked, bail */
 122         "       sub     %[val], %[val], 1       \n"     /* counter-- */
 123         "       scond   %[val], [%[rwlock]]     \n"
 124         "       bnz     1b                      \n"     /* retry if collided with someone */
 125         "       mov     %[got_it], 1            \n"
 126         "                                       \n"
 127         "4: ; --- done ---                      \n"
 128
 129         : [val]         "=&r"   (val),
 130           [got_it]      "+&r"   (got_it)
 131         : [rwlock]      "r"     (&(rw->counter)),
 132           [WR_LOCKED]   "ir"    (0)
 133         : "memory", "cc");
 134
 135         smp_mb();
 136
 137         return got_it;
 138 }
 139
 140 static inline void arch_write_lock(arch_rwlock_t *rw)
 141 {
 142         unsigned int val;
 143
 144         smp_mb();
 145
 146         /*
 147          * If reader(s) hold lock (lock < __ARCH_RW_LOCK_UNLOCKED__),
 148          * deny writer. Otherwise if unlocked grant to writer
 149          * Hence the claim that Linux rwlocks are unfair to writers.
 150          * (can be starved for an indefinite time by readers).
 151          *
 152          *      if (rw->counter == __ARCH_RW_LOCK_UNLOCKED__) {
 153          *              rw->counter = 0;
 154          *              ret = 1;
 155          *      }
 156          */
 157
 158         __asm__ __volatile__(
 159         "1:     llock   %[val], [%[rwlock]]     \n"
 160         "       brne    %[val], %[UNLOCKED], 1b \n"     /* while !UNLOCKED spin */
 161         "       mov     %[val], %[WR_LOCKED]    \n"
 162         "       scond   %[val], [%[rwlock]]     \n"
 163         "       bnz     1b                      \n"
 164         "                                       \n"
 165         : [val]         "=&r"   (val)
 166         : [rwlock]      "r"     (&(rw->counter)),
 167           [UNLOCKED]    "ir"    (__ARCH_RW_LOCK_UNLOCKED__),
 168           [WR_LOCKED]   "ir"    (0)
 169         : "memory", "cc");
 170
 171         smp_mb();
 172 }
 173
 174 /* 1 - lock taken successfully */
 175 static inline int arch_write_trylock(arch_rwlock_t *rw)
 176 {
 177         unsigned int val, got_it = 0;
 178
 179         smp_mb();
 180
 181         __asm__ __volatile__(
 182         "1:     llock   %[val], [%[rwlock]]     \n"
 183         "       brne    %[val], %[UNLOCKED], 4f \n"     /* !UNLOCKED, bail */
 184         "       mov     %[val], %[WR_LOCKED]    \n"
 185         "       scond   %[val], [%[rwlock]]     \n"
 186         "       bnz     1b                      \n"     /* retry if collided with someone */
 187         "       mov     %[got_it], 1            \n"
 188         "                                       \n"
 189         "4: ; --- done ---                      \n"
 190
 191         : [val]         "=&r"   (val),
 192           [got_it]      "+&r"   (got_it)
 193         : [rwlock]      "r"     (&(rw->counter)),
 194           [UNLOCKED]    "ir"    (__ARCH_RW_LOCK_UNLOCKED__),
 195           [WR_LOCKED]   "ir"    (0)
 196         : "memory", "cc");
 197
 198         smp_mb();
 199
 200         return got_it;
 201 }
 202
 203 static inline void arch_read_unlock(arch_rwlock_t *rw)
 204 {
 205         unsigned int val;
 206
 207         smp_mb();
 208
 209         /*
 210          * rw->counter++;
 211          */
 212         __asm__ __volatile__(
 213         "1:     llock   %[val], [%[rwlock]]     \n"
 214         "       add     %[val], %[val], 1       \n"
 215         "       scond   %[val], [%[rwlock]]     \n"
 216         "       bnz     1b                      \n"
 217         "                                       \n"
 218         : [val]         "=&r"   (val)
 219         : [rwlock]      "r"     (&(rw->counter))
 220         : "memory", "cc");
 221
 222         smp_mb();
 223 }
 224
 225 static inline void arch_write_unlock(arch_rwlock_t *rw)
 226 {
 227         smp_mb();
 228
 229         rw->counter = __ARCH_RW_LOCK_UNLOCKED__;
 230
 231         smp_mb();
 232 }
 233
 234 #else   /* !CONFIG_ARC_HAS_LLSC */
 235
 236 static inline void arch_spin_lock(arch_spinlock_t *lock)
 237 {
 238         unsigned int val = __ARCH_SPIN_LOCK_LOCKED__;
 239
 240         /*
 241          * This smp_mb() is technically superfluous, we only need the one
 242          * after the lock for providing the ACQUIRE semantics.
 243          * However doing the "right" thing was regressing hackbench
 244          * so keeping this, pending further investigation
 245          */
 246         smp_mb();
 247
 248         __asm__ __volatile__(
 249         "1:     ex  %0, [%1]            \n"
 250 #ifdef CONFIG_EZNPS_MTM_EXT
 251         "       .word %3                \n"
 252 #endif
 253         "       breq  %0, %2, 1b        \n"
 254         : "+&r" (val)
 255         : "r"(&(lock->slock)), "ir"(__ARCH_SPIN_LOCK_LOCKED__)
 256 #ifdef CONFIG_EZNPS_MTM_EXT
 257         , "i"(CTOP_INST_SCHD_RW)
 258 #endif
 259         : "memory");
 260
 261         /*
 262          * ACQUIRE barrier to ensure load/store after taking the lock
 263          * don't "bleed-up" out of the critical section (leak-in is allowed)
 264          * http://www.spinics.net/lists/kernel/msg2010409.html
 265          *
 266          * ARCv2 only has load-load, store-store and all-all barrier
 267          * thus need the full all-all barrier
 268          */
 269         smp_mb();
 270 }
 271
 272 /* 1 - lock taken successfully */
 273 static inline int arch_spin_trylock(arch_spinlock_t *lock)
 274 {
 275         unsigned int val = __ARCH_SPIN_LOCK_LOCKED__;
 276
 277         smp_mb();
 278
 279         __asm__ __volatile__(
 280         "1:     ex  %0, [%1]            \n"
 281         : "+r" (val)
 282         : "r"(&(lock->slock))
 283         : "memory");
 284
 285         smp_mb();
 286
 287         return (val == __ARCH_SPIN_LOCK_UNLOCKED__);
 288 }
 289
 290 static inline void arch_spin_unlock(arch_spinlock_t *lock)
 291 {
 292         unsigned int val = __ARCH_SPIN_LOCK_UNLOCKED__;
 293
 294         /*
 295          * RELEASE barrier: given the instructions avail on ARCv2, full barrier
 296          * is the only option
 297          */
 298         smp_mb();
 299
 300         /*
 301          * EX is not really required here, a simple STore of 0 suffices.
 302          * However this causes tasklist livelocks in SystemC based SMP virtual
 303          * platforms where the systemc core scheduler uses EX as a cue for
 304          * moving to next core. Do a git log of this file for details
 305          */
 306         __asm__ __volatile__(
 307         "       ex  %0, [%1]            \n"
 308         : "+r" (val)
 309         : "r"(&(lock->slock))
 310         : "memory");
 311
 312         /*
 313          * superfluous, but keeping for now - see pairing version in
 314          * arch_spin_lock above
 315          */
 316         smp_mb();
 317 }
 318
 319 /*
 320  * Read-write spinlocks, allowing multiple readers but only one writer.
 321  * Unfair locking as Writers could be starved indefinitely by Reader(s)
 322  *
 323  * The spinlock itself is contained in @counter and access to it is
 324  * serialized with @lock_mutex.
 325  */
 326
 327 /* 1 - lock taken successfully */
 328 static inline int arch_read_trylock(arch_rwlock_t *rw)
 329 {
 330         int ret = 0;
 331         unsigned long flags;
 332
 333         local_irq_save(flags);
 334         arch_spin_lock(&(rw->lock_mutex));
 335
 336         /*
 337          * zero means writer holds the lock exclusively, deny Reader.
 338          * Otherwise grant lock to first/subseq reader
 339          */
 340         if (rw->counter > 0) {
 341                 rw->counter--;
 342                 ret = 1;
 343         }
 344
 345         arch_spin_unlock(&(rw->lock_mutex));
 346         local_irq_restore(flags);
 347
 348         smp_mb();
 349         return ret;
 350 }
 351
 352 /* 1 - lock taken successfully */
 353 static inline int arch_write_trylock(arch_rwlock_t *rw)
 354 {
 355         int ret = 0;
 356         unsigned long flags;
 357
 358         local_irq_save(flags);
 359         arch_spin_lock(&(rw->lock_mutex));
 360
 361         /*
 362          * If reader(s) hold lock (lock < __ARCH_RW_LOCK_UNLOCKED__),
 363          * deny writer. Otherwise if unlocked grant to writer
 364          * Hence the claim that Linux rwlocks are unfair to writers.
 365          * (can be starved for an indefinite time by readers).
 366          */
 367         if (rw->counter == __ARCH_RW_LOCK_UNLOCKED__) {
 368                 rw->counter = 0;
 369                 ret = 1;
 370         }
 371         arch_spin_unlock(&(rw->lock_mutex));
 372         local_irq_restore(flags);
 373
 374         return ret;
 375 }
 376
 377 static inline void arch_read_lock(arch_rwlock_t *rw)
 378 {
 379         while (!arch_read_trylock(rw))
 380                 cpu_relax();
 381 }
 382
 383 static inline void arch_write_lock(arch_rwlock_t *rw)
 384 {
 385         while (!arch_write_trylock(rw))
 386                 cpu_relax();
 387 }
 388
 389 static inline void arch_read_unlock(arch_rwlock_t *rw)
 390 {
 391         unsigned long flags;
 392
 393         local_irq_save(flags);
 394         arch_spin_lock(&(rw->lock_mutex));
 395         rw->counter++;
 396         arch_spin_unlock(&(rw->lock_mutex));
 397         local_irq_restore(flags);
 398 }
 399
 400 static inline void arch_write_unlock(arch_rwlock_t *rw)
 401 {
 402         unsigned long flags;
 403
 404         local_irq_save(flags);
 405         arch_spin_lock(&(rw->lock_mutex));
 406         rw->counter = __ARCH_RW_LOCK_UNLOCKED__;
 407         arch_spin_unlock(&(rw->lock_mutex));
 408         local_irq_restore(flags);
 409 }
 410
 411 #endif
 412
 413 #define arch_read_can_lock(x)   ((x)->counter > 0)
 414 #define arch_write_can_lock(x)  ((x)->counter == __ARCH_RW_LOCK_UNLOCKED__)
 415
 416 #define arch_read_lock_flags(lock, flags)       arch_read_lock(lock)
 417 #define arch_write_lock_flags(lock, flags)      arch_write_lock(lock)
 418
 419 #define arch_spin_relax(lock)   cpu_relax()
 420 #define arch_read_relax(lock)   cpu_relax()
 421 #define arch_write_relax(lock)  cpu_relax()
 422
 423 #endif /* __ASM_SPINLOCK_H */