arch/arm/include/asm/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.  If it is zero, we may have
  12  * won the lock, so we try exclusively storing it.  A memory barrier
  13  * is required after we get a lock, and before we release it, because
  14  * V6 CPUs are assumed to have weakly ordered memory.
  15  *
  16  * Unlocked value: 0
  17  * Locked value: 1
  18  */
  19
  20 #define __raw_spin_is_locked(x)         ((x)->lock != 0)
  21 #define __raw_spin_unlock_wait(lock) \
  22         do { while (__raw_spin_is_locked(lock)) cpu_relax(); } while (0)
  23
  24 #define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
  25
  26 static inline void __raw_spin_lock(raw_spinlock_t *lock)
  27 {
  28         unsigned long tmp;
  29
  30         __asm__ __volatile__(
  31 "1:     ldrex   %0, [%1]\n"
  32 "       teq     %0, #0\n"
  33 #ifdef CONFIG_CPU_32v6K
  34 "       wfene\n"
  35 #endif
  36 "       strexeq %0, %2, [%1]\n"
  37 "       teqeq   %0, #0\n"
  38 "       bne     1b"
  39         : "=&r" (tmp)
  40         : "r" (&lock->lock), "r" (1)
  41         : "cc");
  42
  43         smp_mb();
  44 }
  45
  46 static inline int __raw_spin_trylock(raw_spinlock_t *lock)
  47 {
  48         unsigned long tmp;
  49
  50         __asm__ __volatile__(
  51 "       ldrex   %0, [%1]\n"
  52 "       teq     %0, #0\n"
  53 "       strexeq %0, %2, [%1]"
  54         : "=&r" (tmp)
  55         : "r" (&lock->lock), "r" (1)
  56         : "cc");
  57
  58         if (tmp == 0) {
  59                 smp_mb();
  60                 return 1;
  61         } else {
  62                 return 0;
  63         }
  64 }
  65
  66 static inline void __raw_spin_unlock(raw_spinlock_t *lock)
  67 {
  68         smp_mb();
  69
  70         __asm__ __volatile__(
  71 "       str     %1, [%0]\n"
  72 #ifdef CONFIG_CPU_32v6K
  73 "       mcr     p15, 0, %1, c7, c10, 4\n" /* DSB */
  74 "       sev"
  75 #endif
  76         :
  77         : "r" (&lock->lock), "r" (0)
  78         : "cc");
  79 }
  80
  81 /*
  82  * RWLOCKS
  83  *
  84  *
  85  * Write locks are easy - we just set bit 31.  When unlocking, we can
  86  * just write zero since the lock is exclusively held.
  87  */
  88
  89 static inline void __raw_write_lock(raw_rwlock_t *rw)
  90 {
  91         unsigned long tmp;
  92
  93         __asm__ __volatile__(
  94 "1:     ldrex   %0, [%1]\n"
  95 "       teq     %0, #0\n"
  96 #ifdef CONFIG_CPU_32v6K
  97 "       wfene\n"
  98 #endif
  99 "       strexeq %0, %2, [%1]\n"
 100 "       teq     %0, #0\n"
 101 "       bne     1b"
 102         : "=&r" (tmp)
 103         : "r" (&rw->lock), "r" (0x80000000)
 104         : "cc");
 105
 106         smp_mb();
 107 }
 108
 109 static inline int __raw_write_trylock(raw_rwlock_t *rw)
 110 {
 111         unsigned long tmp;
 112
 113         __asm__ __volatile__(
 114 "1:     ldrex   %0, [%1]\n"
 115 "       teq     %0, #0\n"
 116 "       strexeq %0, %2, [%1]"
 117         : "=&r" (tmp)
 118         : "r" (&rw->lock), "r" (0x80000000)
 119         : "cc");
 120
 121         if (tmp == 0) {
 122                 smp_mb();
 123                 return 1;
 124         } else {
 125                 return 0;
 126         }
 127 }
 128
 129 static inline void __raw_write_unlock(raw_rwlock_t *rw)
 130 {
 131         smp_mb();
 132
 133         __asm__ __volatile__(
 134         "str    %1, [%0]\n"
 135 #ifdef CONFIG_CPU_32v6K
 136 "       mcr     p15, 0, %1, c7, c10, 4\n" /* DSB */
 137 "       sev\n"
 138 #endif
 139         :
 140         : "r" (&rw->lock), "r" (0)
 141         : "cc");
 142 }
 143
 144 /* write_can_lock - would write_trylock() succeed? */
 145 #define __raw_write_can_lock(x)         ((x)->lock == 0)
 146
 147 /*
 148  * Read locks are a bit more hairy:
 149  *  - Exclusively load the lock value.
 150  *  - Increment it.
 151  *  - Store new lock value if positive, and we still own this location.
 152  *    If the value is negative, we've already failed.
 153  *  - If we failed to store the value, we want a negative result.
 154  *  - If we failed, try again.
 155  * Unlocking is similarly hairy.  We may have multiple read locks
 156  * currently active.  However, we know we won't have any write
 157  * locks.
 158  */
 159 static inline void __raw_read_lock(raw_rwlock_t *rw)
 160 {
 161         unsigned long tmp, tmp2;
 162
 163         __asm__ __volatile__(
 164 "1:     ldrex   %0, [%2]\n"
 165 "       adds    %0, %0, #1\n"
 166 "       strexpl %1, %0, [%2]\n"
 167 #ifdef CONFIG_CPU_32v6K
 168 "       wfemi\n"
 169 #endif
 170 "       rsbpls  %0, %1, #0\n"
 171 "       bmi     1b"
 172         : "=&r" (tmp), "=&r" (tmp2)
 173         : "r" (&rw->lock)
 174         : "cc");
 175
 176         smp_mb();
 177 }
 178
 179 static inline void __raw_read_unlock(raw_rwlock_t *rw)
 180 {
 181         unsigned long tmp, tmp2;
 182
 183         smp_mb();
 184
 185         __asm__ __volatile__(
 186 "1:     ldrex   %0, [%2]\n"
 187 "       sub     %0, %0, #1\n"
 188 "       strex   %1, %0, [%2]\n"
 189 "       teq     %1, #0\n"
 190 "       bne     1b"
 191 #ifdef CONFIG_CPU_32v6K
 192 "\n     cmp     %0, #0\n"
 193 "       mcreq   p15, 0, %0, c7, c10, 4\n"
 194 "       seveq"
 195 #endif
 196         : "=&r" (tmp), "=&r" (tmp2)
 197         : "r" (&rw->lock)
 198         : "cc");
 199 }
 200
 201 static inline int __raw_read_trylock(raw_rwlock_t *rw)
 202 {
 203         unsigned long tmp, tmp2 = 1;
 204
 205         __asm__ __volatile__(
 206 "1:     ldrex   %0, [%2]\n"
 207 "       adds    %0, %0, #1\n"
 208 "       strexpl %1, %0, [%2]\n"
 209         : "=&r" (tmp), "+r" (tmp2)
 210         : "r" (&rw->lock)
 211         : "cc");
 212
 213         smp_mb();
 214         return tmp2 == 0;
 215 }
 216
 217 /* read_can_lock - would read_trylock() succeed? */
 218 #define __raw_read_can_lock(x)          ((x)->lock < 0x80000000)
 219
 220 #define __raw_read_lock_flags(lock, flags) __raw_read_lock(lock)
 221 #define __raw_write_lock_flags(lock, flags) __raw_write_lock(lock)
 222
 223 #define _raw_spin_relax(lock)   cpu_relax()
 224 #define _raw_read_relax(lock)   cpu_relax()
 225 #define _raw_write_relax(lock)  cpu_relax()
 226
 227 #endif /* __ASM_SPINLOCK_H */