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.  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 #define rwlock_is_locked(x)     (*((volatile unsigned int *)(x)) != 0)
  89
  90 static inline void __raw_write_lock(raw_rwlock_t *rw)
  91 {
  92         unsigned long tmp;
  93
  94         __asm__ __volatile__(
  95 "1:     ldrex   %0, [%1]\n"
  96 "       teq     %0, #0\n"
  97 #ifdef CONFIG_CPU_32v6K
  98 "       wfene\n"
  99 #endif
 100 "       strexeq %0, %2, [%1]\n"
 101 "       teq     %0, #0\n"
 102 "       bne     1b"
 103         : "=&r" (tmp)
 104         : "r" (&rw->lock), "r" (0x80000000)
 105         : "cc");
 106
 107         smp_mb();
 108 }
 109
 110 static inline int __raw_write_trylock(raw_rwlock_t *rw)
 111 {
 112         unsigned long tmp;
 113
 114         __asm__ __volatile__(
 115 "1:     ldrex   %0, [%1]\n"
 116 "       teq     %0, #0\n"
 117 "       strexeq %0, %2, [%1]"
 118         : "=&r" (tmp)
 119         : "r" (&rw->lock), "r" (0x80000000)
 120         : "cc");
 121
 122         if (tmp == 0) {
 123                 smp_mb();
 124                 return 1;
 125         } else {
 126                 return 0;
 127         }
 128 }
 129
 130 static inline void __raw_write_unlock(raw_rwlock_t *rw)
 131 {
 132         smp_mb();
 133
 134         __asm__ __volatile__(
 135         "str    %1, [%0]\n"
 136 #ifdef CONFIG_CPU_32v6K
 137 "       mcr     p15, 0, %1, c7, c10, 4\n" /* DSB */
 138 "       sev\n"
 139 #endif
 140         :
 141         : "r" (&rw->lock), "r" (0)
 142         : "cc");
 143 }
 144
 145 /* write_can_lock - would write_trylock() succeed? */
 146 #define __raw_write_can_lock(x)         ((x)->lock == 0x80000000)
 147
 148 /*
 149  * Read locks are a bit more hairy:
 150  *  - Exclusively load the lock value.
 151  *  - Increment it.
 152  *  - Store new lock value if positive, and we still own this location.
 153  *    If the value is negative, we've already failed.
 154  *  - If we failed to store the value, we want a negative result.
 155  *  - If we failed, try again.
 156  * Unlocking is similarly hairy.  We may have multiple read locks
 157  * currently active.  However, we know we won't have any write
 158  * locks.
 159  */
 160 static inline void __raw_read_lock(raw_rwlock_t *rw)
 161 {
 162         unsigned long tmp, tmp2;
 163
 164         __asm__ __volatile__(
 165 "1:     ldrex   %0, [%2]\n"
 166 "       adds    %0, %0, #1\n"
 167 "       strexpl %1, %0, [%2]\n"
 168 #ifdef CONFIG_CPU_32v6K
 169 "       wfemi\n"
 170 #endif
 171 "       rsbpls  %0, %1, #0\n"
 172 "       bmi     1b"
 173         : "=&r" (tmp), "=&r" (tmp2)
 174         : "r" (&rw->lock)
 175         : "cc");
 176
 177         smp_mb();
 178 }
 179
 180 static inline void __raw_read_unlock(raw_rwlock_t *rw)
 181 {
 182         unsigned long tmp, tmp2;
 183
 184         smp_mb();
 185
 186         __asm__ __volatile__(
 187 "1:     ldrex   %0, [%2]\n"
 188 "       sub     %0, %0, #1\n"
 189 "       strex   %1, %0, [%2]\n"
 190 "       teq     %1, #0\n"
 191 "       bne     1b"
 192 #ifdef CONFIG_CPU_32v6K
 193 "\n     cmp     %0, #0\n"
 194 "       mcreq   p15, 0, %0, c7, c10, 4\n"
 195 "       seveq"
 196 #endif
 197         : "=&r" (tmp), "=&r" (tmp2)
 198         : "r" (&rw->lock)
 199         : "cc");
 200 }
 201
 202 static inline int __raw_read_trylock(raw_rwlock_t *rw)
 203 {
 204         unsigned long tmp, tmp2 = 1;
 205
 206         __asm__ __volatile__(
 207 "1:     ldrex   %0, [%2]\n"
 208 "       adds    %0, %0, #1\n"
 209 "       strexpl %1, %0, [%2]\n"
 210         : "=&r" (tmp), "+r" (tmp2)
 211         : "r" (&rw->lock)
 212         : "cc");
 213
 214         smp_mb();
 215         return tmp2 == 0;
 216 }
 217
 218 /* read_can_lock - would read_trylock() succeed? */
 219 #define __raw_read_can_lock(x)          ((x)->lock < 0x80000000)
 220
 221 #define _raw_spin_relax(lock)   cpu_relax()
 222 #define _raw_read_relax(lock)   cpu_relax()
 223 #define _raw_write_relax(lock)  cpu_relax()
 224
 225 #endif /* __ASM_SPINLOCK_H */