include/asm-arm/spinlock.h

   1 #ifndef __ASM_SPINLOCK_H
   2 #define __ASM_SPINLOCK_H
   3
   4 #if __LINUX_ARM_ARCH__ < 6
   5 #error SMP not supported on pre-ARMv6 CPUs
   6 #endif
   7
   8 /*
   9  * ARMv6 Spin-locking.
  10  *
  11  * We (exclusively) read the old value, and decrement it.  If it
  12  * hits zero, we may have won the lock, so we try (exclusively)
  13  * storing it.
  14  *
  15  * Unlocked value: 0
  16  * Locked value: 1
  17  */
  18 typedef struct {
  19         volatile unsigned int lock;
  20 #ifdef CONFIG_PREEMPT
  21         unsigned int break_lock;
  22 #endif
  23 } spinlock_t;
  24
  25 #define SPIN_LOCK_UNLOCKED      (spinlock_t) { 0 }
  26
  27 #define spin_lock_init(x)       do { *(x) = SPIN_LOCK_UNLOCKED; } while (0)
  28 #define spin_is_locked(x)       ((x)->lock != 0)
  29 #define spin_unlock_wait(x)     do { barrier(); } while (spin_is_locked(x))
  30 #define _raw_spin_lock_flags(lock, flags) _raw_spin_lock(lock)
  31
  32 static inline void _raw_spin_lock(spinlock_t *lock)
  33 {
  34         unsigned long tmp;
  35
  36         __asm__ __volatile__(
  37 "1:     ldrex   %0, [%1]\n"
  38 "       teq     %0, #0\n"
  39 "       strexeq %0, %2, [%1]\n"
  40 "       teqeq   %0, #0\n"
  41 "       bne     1b"
  42         : "=&r" (tmp)
  43         : "r" (&lock->lock), "r" (1)
  44         : "cc", "memory");
  45 }
  46
  47 static inline int _raw_spin_trylock(spinlock_t *lock)
  48 {
  49         unsigned long tmp;
  50
  51         __asm__ __volatile__(
  52 "       ldrex   %0, [%1]\n"
  53 "       teq     %0, #0\n"
  54 "       strexeq %0, %2, [%1]"
  55         : "=&r" (tmp)
  56         : "r" (&lock->lock), "r" (1)
  57         : "cc", "memory");
  58
  59         return tmp == 0;
  60 }
  61
  62 static inline void _raw_spin_unlock(spinlock_t *lock)
  63 {
  64         __asm__ __volatile__(
  65 "       str     %1, [%0]"
  66         :
  67         : "r" (&lock->lock), "r" (0)
  68         : "cc", "memory");
  69 }
  70
  71 /*
  72  * RWLOCKS
  73  */
  74 typedef struct {
  75         volatile unsigned int lock;
  76 #ifdef CONFIG_PREEMPT
  77         unsigned int break_lock;
  78 #endif
  79 } rwlock_t;
  80
  81 #define RW_LOCK_UNLOCKED        (rwlock_t) { 0 }
  82 #define rwlock_init(x)          do { *(x) = RW_LOCK_UNLOCKED; } while (0)
  83 #define rwlock_is_locked(x)     (*((volatile unsigned int *)(x)) != 0)
  84
  85 /*
  86  * Write locks are easy - we just set bit 31.  When unlocking, we can
  87  * just write zero since the lock is exclusively held.
  88  */
  89 static inline void _raw_write_lock(rwlock_t *rw)
  90 {
  91         unsigned long tmp;
  92
  93         __asm__ __volatile__(
  94 "1:     ldrex   %0, [%1]\n"
  95 "       teq     %0, #0\n"
  96 "       strexeq %0, %2, [%1]\n"
  97 "       teq     %0, #0\n"
  98 "       bne     1b"
  99         : "=&r" (tmp)
 100         : "r" (&rw->lock), "r" (0x80000000)
 101         : "cc", "memory");
 102 }
 103
 104 static inline int _raw_write_trylock(rwlock_t *rw)
 105 {
 106         unsigned long tmp;
 107
 108         __asm__ __volatile__(
 109 "1:     ldrex   %0, [%1]\n"
 110 "       teq     %0, #0\n"
 111 "       strexeq %0, %2, [%1]"
 112         : "=&r" (tmp)
 113         : "r" (&rw->lock), "r" (0x80000000)
 114         : "cc", "memory");
 115
 116         return tmp == 0;
 117 }
 118
 119 static inline void _raw_write_unlock(rwlock_t *rw)
 120 {
 121         __asm__ __volatile__(
 122         "str    %1, [%0]"
 123         :
 124         : "r" (&rw->lock), "r" (0)
 125         : "cc", "memory");
 126 }
 127
 128 /*
 129  * Read locks are a bit more hairy:
 130  *  - Exclusively load the lock value.
 131  *  - Increment it.
 132  *  - Store new lock value if positive, and we still own this location.
 133  *    If the value is negative, we've already failed.
 134  *  - If we failed to store the value, we want a negative result.
 135  *  - If we failed, try again.
 136  * Unlocking is similarly hairy.  We may have multiple read locks
 137  * currently active.  However, we know we won't have any write
 138  * locks.
 139  */
 140 static inline void _raw_read_lock(rwlock_t *rw)
 141 {
 142         unsigned long tmp, tmp2;
 143
 144         __asm__ __volatile__(
 145 "1:     ldrex   %0, [%2]\n"
 146 "       adds    %0, %0, #1\n"
 147 "       strexpl %1, %0, [%2]\n"
 148 "       rsbpls  %0, %1, #0\n"
 149 "       bmi     1b"
 150         : "=&r" (tmp), "=&r" (tmp2)
 151         : "r" (&rw->lock)
 152         : "cc", "memory");
 153 }
 154
 155 static inline void _raw_read_unlock(rwlock_t *rw)
 156 {
 157         unsigned long tmp, tmp2;
 158
 159         __asm__ __volatile__(
 160 "1:     ldrex   %0, [%2]\n"
 161 "       sub     %0, %0, #1\n"
 162 "       strex   %1, %0, [%2]\n"
 163 "       teq     %1, #0\n"
 164 "       bne     1b"
 165         : "=&r" (tmp), "=&r" (tmp2)
 166         : "r" (&rw->lock)
 167         : "cc", "memory");
 168 }
 169
 170 #define _raw_read_trylock(lock) generic_raw_read_trylock(lock)
 171
 172 #endif /* __ASM_SPINLOCK_H */