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 #include <asm/processor.h>
   9
  10 /*
  11  * sev and wfe are ARMv6K extensions.  Uniprocessor ARMv6 may not have the K
  12  * extensions, so when running on UP, we have to patch these instructions away.
  13  */
  14 #define ALT_SMP(smp, up)                                        \
  15         "9998:  " smp "\n"                                      \
  16         "       .pushsection \".alt.smp.init\", \"a\"\n"        \
  17         "       .long   9998b\n"                                \
  18         "       " up "\n"                                       \
  19         "       .popsection\n"
  20
  21 #ifdef CONFIG_THUMB2_KERNEL
  22 #define SEV             ALT_SMP("sev.w", "nop.w")
  23 /*
  24  * For Thumb-2, special care is needed to ensure that the conditional WFE
  25  * instruction really does assemble to exactly 4 bytes (as required by
  26  * the SMP_ON_UP fixup code).   By itself "wfene" might cause the
  27  * assembler to insert a extra (16-bit) IT instruction, depending on the
  28  * presence or absence of neighbouring conditional instructions.
  29  *
  30  * To avoid this unpredictableness, an approprite IT is inserted explicitly:
  31  * the assembler won't change IT instructions which are explicitly present
  32  * in the input.
  33  */
  34 #define WFE(cond)       ALT_SMP(                \
  35         "it " cond "\n\t"                       \
  36         "wfe" cond ".n",                        \
  37                                                 \
  38         "nop.w"                                 \
  39 )
  40 #else
  41 #define SEV             ALT_SMP("sev", "nop")
  42 #define WFE(cond)       ALT_SMP("wfe" cond, "nop")
  43 #endif
  44
  45 static inline void dsb_sev(void)
  46 {
  47 #if __LINUX_ARM_ARCH__ >= 7
  48         __asm__ __volatile__ (
  49                 "dsb\n"
  50                 SEV
  51         );
  52 #else
  53         __asm__ __volatile__ (
  54                 "mcr p15, 0, %0, c7, c10, 4\n"
  55                 SEV
  56                 : : "r" (0)
  57         );
  58 #endif
  59 }
  60
  61 /*
  62  * ARMv6 ticket-based spin-locking.
  63  *
  64  * A memory barrier is required after we get a lock, and before we
  65  * release it, because V6 CPUs are assumed to have weakly ordered
  66  * memory.
  67  */
  68
  69 #define arch_spin_unlock_wait(lock) \
  70         do { while (arch_spin_is_locked(lock)) cpu_relax(); } while (0)
  71
  72 #define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
  73
  74 static inline void arch_spin_lock(arch_spinlock_t *lock)
  75 {
  76         unsigned long tmp;
  77         u32 newval;
  78         arch_spinlock_t lockval;
  79
  80         __asm__ __volatile__(
  81 "1:     ldrex   %0, [%3]\n"
  82 "       add     %1, %0, %4\n"
  83 "       strex   %2, %1, [%3]\n"
  84 "       teq     %2, #0\n"
  85 "       bne     1b"
  86         : "=&r" (lockval), "=&r" (newval), "=&r" (tmp)
  87         : "r" (&lock->slock), "I" (1 << TICKET_SHIFT)
  88         : "cc");
  89
  90         while (lockval.tickets.next != lockval.tickets.owner) {
  91                 wfe();
  92                 lockval.tickets.owner = ACCESS_ONCE(lock->tickets.owner);
  93         }
  94
  95         smp_mb();
  96 }
  97
  98 static inline int arch_spin_trylock(arch_spinlock_t *lock)
  99 {
 100         unsigned long contended, res;
 101         u32 slock;
 102
 103         do {
 104                 __asm__ __volatile__(
 105                 "       ldrex   %0, [%3]\n"
 106                 "       mov     %2, #0\n"
 107                 "       subs    %1, %0, %0, ror #16\n"
 108                 "       addeq   %0, %0, %4\n"
 109                 "       strexeq %2, %0, [%3]"
 110                 : "=&r" (slock), "=&r" (contended), "=&r" (res)
 111                 : "r" (&lock->slock), "I" (1 << TICKET_SHIFT)
 112                 : "cc");
 113         } while (res);
 114
 115         if (!contended) {
 116                 smp_mb();
 117                 return 1;
 118         } else {
 119                 return 0;
 120         }
 121 }
 122
 123 static inline void arch_spin_unlock(arch_spinlock_t *lock)
 124 {
 125         smp_mb();
 126         lock->tickets.owner++;
 127         dsb_sev();
 128 }
 129
 130 static inline int arch_spin_is_locked(arch_spinlock_t *lock)
 131 {
 132         struct __raw_tickets tickets = ACCESS_ONCE(lock->tickets);
 133         return tickets.owner != tickets.next;
 134 }
 135
 136 static inline int arch_spin_is_contended(arch_spinlock_t *lock)
 137 {
 138         struct __raw_tickets tickets = ACCESS_ONCE(lock->tickets);
 139         return (tickets.next - tickets.owner) > 1;
 140 }
 141 #define arch_spin_is_contended  arch_spin_is_contended
 142
 143 /*
 144  * RWLOCKS
 145  *
 146  *
 147  * Write locks are easy - we just set bit 31.  When unlocking, we can
 148  * just write zero since the lock is exclusively held.
 149  */
 150
 151 static inline void arch_write_lock(arch_rwlock_t *rw)
 152 {
 153         unsigned long tmp;
 154
 155         __asm__ __volatile__(
 156 "1:     ldrex   %0, [%1]\n"
 157 "       teq     %0, #0\n"
 158         WFE("ne")
 159 "       strexeq %0, %2, [%1]\n"
 160 "       teq     %0, #0\n"
 161 "       bne     1b"
 162         : "=&r" (tmp)
 163         : "r" (&rw->lock), "r" (0x80000000)
 164         : "cc");
 165
 166         smp_mb();
 167 }
 168
 169 static inline int arch_write_trylock(arch_rwlock_t *rw)
 170 {
 171         unsigned long contended, res;
 172
 173         do {
 174                 __asm__ __volatile__(
 175                 "       ldrex   %0, [%2]\n"
 176                 "       mov     %1, #0\n"
 177                 "       teq     %0, #0\n"
 178                 "       strexeq %1, %3, [%2]"
 179                 : "=&r" (contended), "=&r" (res)
 180                 : "r" (&rw->lock), "r" (0x80000000)
 181                 : "cc");
 182         } while (res);
 183
 184         if (!contended) {
 185                 smp_mb();
 186                 return 1;
 187         } else {
 188                 return 0;
 189         }
 190 }
 191
 192 static inline void arch_write_unlock(arch_rwlock_t *rw)
 193 {
 194         smp_mb();
 195
 196         __asm__ __volatile__(
 197         "str    %1, [%0]\n"
 198         :
 199         : "r" (&rw->lock), "r" (0)
 200         : "cc");
 201
 202         dsb_sev();
 203 }
 204
 205 /* write_can_lock - would write_trylock() succeed? */
 206 #define arch_write_can_lock(x)          ((x)->lock == 0)
 207
 208 /*
 209  * Read locks are a bit more hairy:
 210  *  - Exclusively load the lock value.
 211  *  - Increment it.
 212  *  - Store new lock value if positive, and we still own this location.
 213  *    If the value is negative, we've already failed.
 214  *  - If we failed to store the value, we want a negative result.
 215  *  - If we failed, try again.
 216  * Unlocking is similarly hairy.  We may have multiple read locks
 217  * currently active.  However, we know we won't have any write
 218  * locks.
 219  */
 220 static inline void arch_read_lock(arch_rwlock_t *rw)
 221 {
 222         unsigned long tmp, tmp2;
 223
 224         __asm__ __volatile__(
 225 "1:     ldrex   %0, [%2]\n"
 226 "       adds    %0, %0, #1\n"
 227 "       strexpl %1, %0, [%2]\n"
 228         WFE("mi")
 229 "       rsbpls  %0, %1, #0\n"
 230 "       bmi     1b"
 231         : "=&r" (tmp), "=&r" (tmp2)
 232         : "r" (&rw->lock)
 233         : "cc");
 234
 235         smp_mb();
 236 }
 237
 238 static inline void arch_read_unlock(arch_rwlock_t *rw)
 239 {
 240         unsigned long tmp, tmp2;
 241
 242         smp_mb();
 243
 244         __asm__ __volatile__(
 245 "1:     ldrex   %0, [%2]\n"
 246 "       sub     %0, %0, #1\n"
 247 "       strex   %1, %0, [%2]\n"
 248 "       teq     %1, #0\n"
 249 "       bne     1b"
 250         : "=&r" (tmp), "=&r" (tmp2)
 251         : "r" (&rw->lock)
 252         : "cc");
 253
 254         if (tmp == 0)
 255                 dsb_sev();
 256 }
 257
 258 static inline int arch_read_trylock(arch_rwlock_t *rw)
 259 {
 260         unsigned long contended, res;
 261
 262         do {
 263                 __asm__ __volatile__(
 264                 "       ldrex   %0, [%2]\n"
 265                 "       mov     %1, #0\n"
 266                 "       adds    %0, %0, #1\n"
 267                 "       strexpl %1, %0, [%2]"
 268                 : "=&r" (contended), "=&r" (res)
 269                 : "r" (&rw->lock)
 270                 : "cc");
 271         } while (res);
 272
 273         /* If the lock is negative, then it is already held for write. */
 274         if (contended < 0x80000000) {
 275                 smp_mb();
 276                 return 1;
 277         } else {
 278                 return 0;
 279         }
 280 }
 281
 282 /* read_can_lock - would read_trylock() succeed? */
 283 #define arch_read_can_lock(x)           ((x)->lock < 0x80000000)
 284
 285 #define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
 286 #define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
 287
 288 #define arch_spin_relax(lock)   cpu_relax()
 289 #define arch_read_relax(lock)   cpu_relax()
 290 #define arch_write_relax(lock)  cpu_relax()
 291
 292 #endif /* __ASM_SPINLOCK_H */