target/linux/ubicom32/files/arch/ubicom32/include/asm/spinlock.h

   1 /*
   2  * arch/ubicom32/include/asm/spinlock.h
   3  *   Spinlock related definitions for Ubicom32 architecture.
   4  *
   5  * (C) Copyright 2009, Ubicom, Inc.
   6  *
   7  * This file is part of the Ubicom32 Linux Kernel Port.
   8  *
   9  * The Ubicom32 Linux Kernel Port is free software: you can redistribute
  10  * it and/or modify it under the terms of the GNU General Public License
  11  * as published by the Free Software Foundation, either version 2 of the
  12  * License, or (at your option) any later version.
  13  *
  14  * The Ubicom32 Linux Kernel Port is distributed in the hope that it
  15  * will be useful, but WITHOUT ANY WARRANTY; without even the implied
  16  * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
  17  * the GNU General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU General Public License
  20  * along with the Ubicom32 Linux Kernel Port.  If not,
  21  * see <http://www.gnu.org/licenses/>.
  22  *
  23  * Ubicom32 implementation derived from (with many thanks):
  24  *   arch/m68knommu
  25  *   arch/blackfin
  26  *   arch/parisc
  27  */
  28 #ifndef _ASM_UBICOM32_SPINLOCK_H
  29 #define _ASM_UBICOM32_SPINLOCK_H
  30
  31 #include <asm/system.h>
  32 #include <asm/processor.h>
  33 #include <asm/spinlock_types.h>
  34
  35 /*
  36  * __raw_spin_lock()
  37  *      Lock the lock.
  38  */
  39 static inline void __raw_spin_lock(raw_spinlock_t *x)
  40 {
  41         asm volatile (
  42         "1:     bset    %0, %0, #0      \n\t"
  43         "       jmpne.f 1b              \n\t"
  44                 : "+U4" (x->lock)
  45                 :
  46                 : "memory", "cc"
  47         );
  48 }
  49
  50 /*
  51  * __raw_spin_unlock()
  52  *      Unlock the lock.
  53  */
  54 static inline void __raw_spin_unlock(raw_spinlock_t *x)
  55 {
  56         asm volatile (
  57         "       bclr    %0, %0, #0      \n\t"
  58                 : "+U4" (x->lock)
  59                 :
  60                 : "memory", "cc"
  61         );
  62 }
  63
  64 /*
  65  * __raw_spin_is_locked()
  66  *      Test if the lock is locked.
  67  */
  68 static inline int __raw_spin_is_locked(raw_spinlock_t *x)
  69 {
  70         return x->lock;
  71 }
  72
  73 /*
  74  * __raw_spin_unlock_wait()
  75  *      Wait for the lock to be unlocked.
  76  *
  77  * Note: the caller has not guarantee that the lock will not
  78  * be acquired before they get to it.
  79  */
  80 static inline void __raw_spin_unlock_wait(raw_spinlock_t *x)
  81 {
  82         do {
  83                 cpu_relax();
  84         } while (__raw_spin_is_locked(x));
  85 }
  86
  87 /*
  88  * __raw_spin_trylock()
  89  *      Try the lock, return 0 on failure, 1 on success.
  90  */
  91 static inline int __raw_spin_trylock(raw_spinlock_t *x)
  92 {
  93         int ret = 0;
  94
  95         asm volatile (
  96         "       bset    %1, %1, #0      \n\t"
  97         "       jmpne.f 1f              \n\t"
  98         "       move.4  %0, #1          \n\t"
  99         "1:                             \n\t"
 100                 : "+r" (ret), "+U4" (x->lock)
 101                 :
 102                 : "memory", "cc"
 103         );
 104
 105         return ret;
 106 }
 107
 108 /*
 109  * __raw_spin_lock_flags()
 110  *      Spin waiting for the lock (enabling IRQ(s))
 111  */
 112 static inline void __raw_spin_lock_flags(raw_spinlock_t *x, unsigned long flags)
 113 {
 114         mb();
 115         while (!__raw_spin_trylock(x)) {
 116                 /*
 117                  * If the flags from the IRQ are set, interrupts are disabled and we
 118                  * need to re-enable them.
 119                  */
 120                 if (!flags) {
 121                         cpu_relax();
 122                 } else {
 123                         raw_local_irq_enable();
 124                         cpu_relax();
 125                         raw_local_irq_disable();
 126                 }
 127         }
 128         mb();
 129 }
 130
 131 /*
 132  * Read-write spinlocks, allowing multiple readers but only one writer.
 133  * Linux rwlocks are unfair to writers; they can be starved for an indefinite
 134  * time by readers.  With care, they can also be taken in interrupt context.
 135  *
 136  * In Ubicom32 architecture implementation, we have a spinlock and a counter.
 137  * Readers use the lock to serialise their access to the counter (which
 138  * records how many readers currently hold the lock).
 139  * Writers hold the spinlock, preventing any readers or other writers from
 140  * grabbing the rwlock.
 141  */
 142
 143 /*
 144  * __raw_read_lock()
 145  *      Increment the counter in the rwlock.
 146  *
 147  * Note that we have to ensure interrupts are disabled in case we're
 148  * interrupted by some other code that wants to grab the same read lock
 149  */
 150 static inline void __raw_read_lock(raw_rwlock_t *rw)
 151 {
 152         unsigned long flags;
 153         raw_local_irq_save(flags);
 154         __raw_spin_lock_flags(&rw->lock, flags);
 155         rw->counter++;
 156         __raw_spin_unlock(&rw->lock);
 157         raw_local_irq_restore(flags);
 158 }
 159
 160 /*
 161  * __raw_read_unlock()
 162  *      Decrement the counter.
 163  *
 164  * Note that we have to ensure interrupts are disabled in case we're
 165  * interrupted by some other code that wants to grab the same read lock
 166  */
 167 static inline void __raw_read_unlock(raw_rwlock_t *rw)
 168 {
 169         unsigned long flags;
 170         raw_local_irq_save(flags);
 171         __raw_spin_lock_flags(&rw->lock, flags);
 172         rw->counter--;
 173         __raw_spin_unlock(&rw->lock);
 174         raw_local_irq_restore(flags);
 175 }
 176
 177 /*
 178  * __raw_read_trylock()
 179  *      Increment the counter if we can.
 180  *
 181  * Note that we have to ensure interrupts are disabled in case we're
 182  * interrupted by some other code that wants to grab the same read lock
 183  */
 184 static inline int __raw_read_trylock(raw_rwlock_t *rw)
 185 {
 186         unsigned long flags;
 187  retry:
 188         raw_local_irq_save(flags);
 189         if (__raw_spin_trylock(&rw->lock)) {
 190                 rw->counter++;
 191                 __raw_spin_unlock(&rw->lock);
 192                 raw_local_irq_restore(flags);
 193                 return 1;
 194         }
 195
 196         raw_local_irq_restore(flags);
 197
 198         /*
 199          * If write-locked, we fail to acquire the lock
 200          */
 201         if (rw->counter < 0) {
 202                 return 0;
 203         }
 204
 205         /*
 206          * Wait until we have a realistic chance at the lock
 207          */
 208         while (__raw_spin_is_locked(&rw->lock) && rw->counter >= 0) {
 209                 cpu_relax();
 210         }
 211
 212         goto retry;
 213 }
 214
 215 /*
 216  * __raw_write_lock()
 217  *
 218  * Note that we have to ensure interrupts are disabled in case we're
 219  * interrupted by some other code that wants to read_trylock() this lock
 220  */
 221 static inline void __raw_write_lock(raw_rwlock_t *rw)
 222 {
 223         unsigned long flags;
 224 retry:
 225         raw_local_irq_save(flags);
 226         __raw_spin_lock_flags(&rw->lock, flags);
 227
 228         if (rw->counter != 0) {
 229                 __raw_spin_unlock(&rw->lock);
 230                 raw_local_irq_restore(flags);
 231
 232                 while (rw->counter != 0)
 233                         cpu_relax();
 234
 235                 goto retry;
 236         }
 237
 238         rw->counter = -1; /* mark as write-locked */
 239         mb();
 240         raw_local_irq_restore(flags);
 241 }
 242
 243 static inline void __raw_write_unlock(raw_rwlock_t *rw)
 244 {
 245         rw->counter = 0;
 246         __raw_spin_unlock(&rw->lock);
 247 }
 248
 249 /* Note that we have to ensure interrupts are disabled in case we're
 250  * interrupted by some other code that wants to read_trylock() this lock */
 251 static inline int __raw_write_trylock(raw_rwlock_t *rw)
 252 {
 253         unsigned long flags;
 254         int result = 0;
 255
 256         raw_local_irq_save(flags);
 257         if (__raw_spin_trylock(&rw->lock)) {
 258                 if (rw->counter == 0) {
 259                         rw->counter = -1;
 260                         result = 1;
 261                 } else {
 262                         /* Read-locked.  Oh well. */
 263                         __raw_spin_unlock(&rw->lock);
 264                 }
 265         }
 266         raw_local_irq_restore(flags);
 267
 268         return result;
 269 }
 270
 271 /*
 272  * read_can_lock - would read_trylock() succeed?
 273  * @lock: the rwlock in question.
 274  */
 275 static inline int __raw_read_can_lock(raw_rwlock_t *rw)
 276 {
 277         return rw->counter >= 0;
 278 }
 279
 280 /*
 281  * write_can_lock - would write_trylock() succeed?
 282  * @lock: the rwlock in question.
 283  */
 284 static inline int __raw_write_can_lock(raw_rwlock_t *rw)
 285 {
 286         return !rw->counter;
 287 }
 288
 289 #define __raw_read_lock_flags(lock, flags) __raw_read_lock(lock)
 290 #define __raw_write_lock_flags(lock, flags) __raw_write_lock(lock)
 291
 292 #define _raw_spin_relax(lock)   cpu_relax()
 293 #define _raw_read_relax(lock)   cpu_relax()
 294 #define _raw_write_relax(lock)  cpu_relax()
 295
 296 #endif /* _ASM_UBICOM32_SPINLOCK_H */