include/asm-i386/spinlock.h

   1 #ifndef __ASM_SPINLOCK_H
   2 #define __ASM_SPINLOCK_H
   3
   4 #include <asm/atomic.h>
   5 #include <asm/rwlock.h>
   6 #include <asm/page.h>
   7 #include <asm/processor.h>
   8 #include <linux/compiler.h>
   9
  10 #ifdef CONFIG_PARAVIRT
  11 #include <asm/paravirt.h>
  12 #else
  13 #define CLI_STRING      "cli"
  14 #define STI_STRING      "sti"
  15 #define CLI_STI_CLOBBERS
  16 #define CLI_STI_INPUT_ARGS
  17 #endif /* CONFIG_PARAVIRT */
  18
  19 /*
  20  * Your basic SMP spinlocks, allowing only a single CPU anywhere
  21  *
  22  * Simple spin lock operations.  There are two variants, one clears IRQ's
  23  * on the local processor, one does not.
  24  *
  25  * We make no fairness assumptions. They have a cost.
  26  *
  27  * (the type definitions are in asm/spinlock_types.h)
  28  */
  29
  30 static inline int __raw_spin_is_locked(raw_spinlock_t *x)
  31 {
  32         return *(volatile signed char *)(&(x)->slock) <= 0;
  33 }
  34
  35 static inline void __raw_spin_lock(raw_spinlock_t *lock)
  36 {
  37         asm volatile("\n1:\t"
  38                      LOCK_PREFIX " ; decb %0\n\t"
  39                      "jns 3f\n"
  40                      "2:\t"
  41                      "rep;nop\n\t"
  42                      "cmpb $0,%0\n\t"
  43                      "jle 2b\n\t"
  44                      "jmp 1b\n"
  45                      "3:\n\t"
  46                      : "+m" (lock->slock) : : "memory");
  47 }
  48
  49 /*
  50  * It is easier for the lock validator if interrupts are not re-enabled
  51  * in the middle of a lock-acquire. This is a performance feature anyway
  52  * so we turn it off:
  53  *
  54  * NOTE: there's an irqs-on section here, which normally would have to be
  55  * irq-traced, but on CONFIG_TRACE_IRQFLAGS we never use this variant.
  56  */
  57 #ifndef CONFIG_PROVE_LOCKING
  58 static inline void __raw_spin_lock_flags(raw_spinlock_t *lock, unsigned long flags)
  59 {
  60         asm volatile(
  61                 "\n1:\t"
  62                 LOCK_PREFIX " ; decb %[slock]\n\t"
  63                 "jns 5f\n"
  64                 "2:\t"
  65                 "testl $0x200, %[flags]\n\t"
  66                 "jz 4f\n\t"
  67                 STI_STRING "\n"
  68                 "3:\t"
  69                 "rep;nop\n\t"
  70                 "cmpb $0, %[slock]\n\t"
  71                 "jle 3b\n\t"
  72                 CLI_STRING "\n\t"
  73                 "jmp 1b\n"
  74                 "4:\t"
  75                 "rep;nop\n\t"
  76                 "cmpb $0, %[slock]\n\t"
  77                 "jg 1b\n\t"
  78                 "jmp 4b\n"
  79                 "5:\n\t"
  80                 : [slock] "+m" (lock->slock)
  81                 : [flags] "r" (flags)
  82                   CLI_STI_INPUT_ARGS
  83                 : "memory" CLI_STI_CLOBBERS);
  84 }
  85 #endif
  86
  87 static inline int __raw_spin_trylock(raw_spinlock_t *lock)
  88 {
  89         char oldval;
  90         asm volatile(
  91                 "xchgb %b0,%1"
  92                 :"=q" (oldval), "+m" (lock->slock)
  93                 :"0" (0) : "memory");
  94         return oldval > 0;
  95 }
  96
  97 /*
  98  * __raw_spin_unlock based on writing $1 to the low byte.
  99  * This method works. Despite all the confusion.
 100  * (except on PPro SMP or if we are using OOSTORE, so we use xchgb there)
 101  * (PPro errata 66, 92)
 102  */
 103
 104 #if !defined(CONFIG_X86_OOSTORE) && !defined(CONFIG_X86_PPRO_FENCE)
 105
 106 static inline void __raw_spin_unlock(raw_spinlock_t *lock)
 107 {
 108         asm volatile("movb $1,%0" : "+m" (lock->slock) :: "memory");
 109 }
 110
 111 #else
 112
 113 static inline void __raw_spin_unlock(raw_spinlock_t *lock)
 114 {
 115         char oldval = 1;
 116
 117         asm volatile("xchgb %b0, %1"
 118                      : "=q" (oldval), "+m" (lock->slock)
 119                      : "0" (oldval) : "memory");
 120 }
 121
 122 #endif
 123
 124 static inline void __raw_spin_unlock_wait(raw_spinlock_t *lock)
 125 {
 126         while (__raw_spin_is_locked(lock))
 127                 cpu_relax();
 128 }
 129
 130 /*
 131  * Read-write spinlocks, allowing multiple readers
 132  * but only one writer.
 133  *
 134  * NOTE! it is quite common to have readers in interrupts
 135  * but no interrupt writers. For those circumstances we
 136  * can "mix" irq-safe locks - any writer needs to get a
 137  * irq-safe write-lock, but readers can get non-irqsafe
 138  * read-locks.
 139  *
 140  * On x86, we implement read-write locks as a 32-bit counter
 141  * with the high bit (sign) being the "contended" bit.
 142  *
 143  * The inline assembly is non-obvious. Think about it.
 144  *
 145  * Changed to use the same technique as rw semaphores.  See
 146  * semaphore.h for details.  -ben
 147  *
 148  * the helpers are in arch/i386/kernel/semaphore.c
 149  */
 150
 151 /**
 152  * read_can_lock - would read_trylock() succeed?
 153  * @lock: the rwlock in question.
 154  */
 155 static inline int __raw_read_can_lock(raw_rwlock_t *x)
 156 {
 157         return (int)(x)->lock > 0;
 158 }
 159
 160 /**
 161  * write_can_lock - would write_trylock() succeed?
 162  * @lock: the rwlock in question.
 163  */
 164 static inline int __raw_write_can_lock(raw_rwlock_t *x)
 165 {
 166         return (x)->lock == RW_LOCK_BIAS;
 167 }
 168
 169 static inline void __raw_read_lock(raw_rwlock_t *rw)
 170 {
 171         asm volatile(LOCK_PREFIX " subl $1,(%0)\n\t"
 172                      "jns 1f\n"
 173                      "call __read_lock_failed\n\t"
 174                      "1:\n"
 175                      ::"a" (rw) : "memory");
 176 }
 177
 178 static inline void __raw_write_lock(raw_rwlock_t *rw)
 179 {
 180         asm volatile(LOCK_PREFIX " subl $" RW_LOCK_BIAS_STR ",(%0)\n\t"
 181                      "jz 1f\n"
 182                      "call __write_lock_failed\n\t"
 183                      "1:\n"
 184                      ::"a" (rw) : "memory");
 185 }
 186
 187 static inline int __raw_read_trylock(raw_rwlock_t *lock)
 188 {
 189         atomic_t *count = (atomic_t *)lock;
 190         atomic_dec(count);
 191         if (atomic_read(count) >= 0)
 192                 return 1;
 193         atomic_inc(count);
 194         return 0;
 195 }
 196
 197 static inline int __raw_write_trylock(raw_rwlock_t *lock)
 198 {
 199         atomic_t *count = (atomic_t *)lock;
 200         if (atomic_sub_and_test(RW_LOCK_BIAS, count))
 201                 return 1;
 202         atomic_add(RW_LOCK_BIAS, count);
 203         return 0;
 204 }
 205
 206 static inline void __raw_read_unlock(raw_rwlock_t *rw)
 207 {
 208         asm volatile(LOCK_PREFIX "incl %0" :"+m" (rw->lock) : : "memory");
 209 }
 210
 211 static inline void __raw_write_unlock(raw_rwlock_t *rw)
 212 {
 213         asm volatile(LOCK_PREFIX "addl $" RW_LOCK_BIAS_STR ", %0"
 214                                  : "+m" (rw->lock) : : "memory");
 215 }
 216
 217 #define _raw_spin_relax(lock)   cpu_relax()
 218 #define _raw_read_relax(lock)   cpu_relax()
 219 #define _raw_write_relax(lock)  cpu_relax()
 220
 221 #endif /* __ASM_SPINLOCK_H */