arch/arc/include/asm/cmpxchg.h

   1 /*
   2  * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  */
   8
   9 #ifndef __ASM_ARC_CMPXCHG_H
  10 #define __ASM_ARC_CMPXCHG_H
  11
  12 #include <linux/types.h>
  13
  14 #include <asm/barrier.h>
  15 #include <asm/smp.h>
  16
  17 #ifdef CONFIG_ARC_HAS_LLSC
  18
  19 static inline unsigned long
  20 __cmpxchg(volatile void *ptr, unsigned long expected, unsigned long new)
  21 {
  22         unsigned long prev;
  23
  24         /*
  25          * Explicit full memory barrier needed before/after as
  26          * LLOCK/SCOND thmeselves don't provide any such semantics
  27          */
  28         smp_mb();
  29
  30         __asm__ __volatile__(
  31         "1:     llock   %0, [%1]        \n"
  32         "       brne    %0, %2, 2f      \n"
  33         "       scond   %3, [%1]        \n"
  34         "       bnz     1b              \n"
  35         "2:                             \n"
  36         : "=&r"(prev)   /* Early clobber, to prevent reg reuse */
  37         : "r"(ptr),     /* Not "m": llock only supports reg direct addr mode */
  38           "ir"(expected),
  39           "r"(new)      /* can't be "ir". scond can't take LIMM for "b" */
  40         : "cc", "memory"); /* so that gcc knows memory is being written here */
  41
  42         smp_mb();
  43
  44         return prev;
  45 }
  46
  47 #elif !defined(CONFIG_ARC_PLAT_EZNPS)
  48
  49 static inline unsigned long
  50 __cmpxchg(volatile void *ptr, unsigned long expected, unsigned long new)
  51 {
  52         unsigned long flags;
  53         int prev;
  54         volatile unsigned long *p = ptr;
  55
  56         /*
  57          * spin lock/unlock provide the needed smp_mb() before/after
  58          */
  59         atomic_ops_lock(flags);
  60         prev = *p;
  61         if (prev == expected)
  62                 *p = new;
  63         atomic_ops_unlock(flags);
  64         return prev;
  65 }
  66
  67 #else /* CONFIG_ARC_PLAT_EZNPS */
  68
  69 static inline unsigned long
  70 __cmpxchg(volatile void *ptr, unsigned long expected, unsigned long new)
  71 {
  72         /*
  73          * Explicit full memory barrier needed before/after
  74          */
  75         smp_mb();
  76
  77         write_aux_reg(CTOP_AUX_GPA1, expected);
  78
  79         __asm__ __volatile__(
  80         "       mov r2, %0\n"
  81         "       mov r3, %1\n"
  82         "       .word %2\n"
  83         "       mov %0, r2"
  84         : "+r"(new)
  85         : "r"(ptr), "i"(CTOP_INST_EXC_DI_R2_R2_R3)
  86         : "r2", "r3", "memory");
  87
  88         smp_mb();
  89
  90         return new;
  91 }
  92
  93 #endif /* CONFIG_ARC_HAS_LLSC */
  94
  95 #define cmpxchg(ptr, o, n) ((typeof(*(ptr)))__cmpxchg((ptr), \
  96                                 (unsigned long)(o), (unsigned long)(n)))
  97
  98 /*
  99  * atomic_cmpxchg is same as cmpxchg
 100  *   LLSC: only different in data-type, semantics are exactly same
 101  *  !LLSC: cmpxchg() has to use an external lock atomic_ops_lock to guarantee
 102  *         semantics, and this lock also happens to be used by atomic_*()
 103  */
 104 #define atomic_cmpxchg(v, o, n) ((int)cmpxchg(&((v)->counter), (o), (n)))
 105
 106
 107 #ifndef CONFIG_ARC_PLAT_EZNPS
 108
 109 /*
 110  * xchg (reg with memory) based on "Native atomic" EX insn
 111  */
 112 static inline unsigned long __xchg(unsigned long val, volatile void *ptr,
 113                                    int size)
 114 {
 115         extern unsigned long __xchg_bad_pointer(void);
 116
 117         switch (size) {
 118         case 4:
 119                 smp_mb();
 120
 121                 __asm__ __volatile__(
 122                 "       ex  %0, [%1]    \n"
 123                 : "+r"(val)
 124                 : "r"(ptr)
 125                 : "memory");
 126
 127                 smp_mb();
 128
 129                 return val;
 130         }
 131         return __xchg_bad_pointer();
 132 }
 133
 134 #define _xchg(ptr, with) ((typeof(*(ptr)))__xchg((unsigned long)(with), (ptr), \
 135                                                  sizeof(*(ptr))))
 136
 137 /*
 138  * xchg() maps directly to ARC EX instruction which guarantees atomicity.
 139  * However in !LLSC config, it also needs to be use @atomic_ops_lock spinlock
 140  * due to a subtle reason:
 141  *  - For !LLSC, cmpxchg() needs to use that lock (see above) and there is lot
 142  *    of  kernel code which calls xchg()/cmpxchg() on same data (see llist.h)
 143  *    Hence xchg() needs to follow same locking rules.
 144  *
 145  * Technically the lock is also needed for UP (boils down to irq save/restore)
 146  * but we can cheat a bit since cmpxchg() atomic_ops_lock() would cause irqs to
 147  * be disabled thus can't possibly be interrpted/preempted/clobbered by xchg()
 148  * Other way around, xchg is one instruction anyways, so can't be interrupted
 149  * as such
 150  */
 151
 152 #if !defined(CONFIG_ARC_HAS_LLSC) && defined(CONFIG_SMP)
 153
 154 #define xchg(ptr, with)                 \
 155 ({                                      \
 156         unsigned long flags;            \
 157         typeof(*(ptr)) old_val;         \
 158                                         \
 159         atomic_ops_lock(flags);         \
 160         old_val = _xchg(ptr, with);     \
 161         atomic_ops_unlock(flags);       \
 162         old_val;                        \
 163 })
 164
 165 #else
 166
 167 #define xchg(ptr, with)  _xchg(ptr, with)
 168
 169 #endif
 170
 171 #else /* CONFIG_ARC_PLAT_EZNPS */
 172
 173 static inline unsigned long __xchg(unsigned long val, volatile void *ptr,
 174                                    int size)
 175 {
 176         extern unsigned long __xchg_bad_pointer(void);
 177
 178         switch (size) {
 179         case 4:
 180                 /*
 181                  * Explicit full memory barrier needed before/after
 182                  */
 183                 smp_mb();
 184
 185                 __asm__ __volatile__(
 186                 "       mov r2, %0\n"
 187                 "       mov r3, %1\n"
 188                 "       .word %2\n"
 189                 "       mov %0, r2\n"
 190                 : "+r"(val)
 191                 : "r"(ptr), "i"(CTOP_INST_XEX_DI_R2_R2_R3)
 192                 : "r2", "r3", "memory");
 193
 194                 smp_mb();
 195
 196                 return val;
 197         }
 198         return __xchg_bad_pointer();
 199 }
 200
 201 #define xchg(ptr, with) ((typeof(*(ptr)))__xchg((unsigned long)(with), (ptr), \
 202                                                  sizeof(*(ptr))))
 203
 204 #endif /* CONFIG_ARC_PLAT_EZNPS */
 205
 206 /*
 207  * "atomic" variant of xchg()
 208  * REQ: It needs to follow the same serialization rules as other atomic_xxx()
 209  * Since xchg() doesn't always do that, it would seem that following defintion
 210  * is incorrect. But here's the rationale:
 211  *   SMP : Even xchg() takes the atomic_ops_lock, so OK.
 212  *   LLSC: atomic_ops_lock are not relevant at all (even if SMP, since LLSC
 213  *         is natively "SMP safe", no serialization required).
 214  *   UP  : other atomics disable IRQ, so no way a difft ctxt atomic_xchg()
 215  *         could clobber them. atomic_xchg() itself would be 1 insn, so it
 216  *         can't be clobbered by others. Thus no serialization required when
 217  *         atomic_xchg is involved.
 218  */
 219 #define atomic_xchg(v, new) (xchg(&((v)->counter), new))
 220
 221 #endif