arch/sparc/include/asm/barrier_64.h

   1 #ifndef __SPARC64_BARRIER_H
   2 #define __SPARC64_BARRIER_H
   3
   4 /* These are here in an effort to more fully work around Spitfire Errata
   5  * #51.  Essentially, if a memory barrier occurs soon after a mispredicted
   6  * branch, the chip can stop executing instructions until a trap occurs.
   7  * Therefore, if interrupts are disabled, the chip can hang forever.
   8  *
   9  * It used to be believed that the memory barrier had to be right in the
  10  * delay slot, but a case has been traced recently wherein the memory barrier
  11  * was one instruction after the branch delay slot and the chip still hung.
  12  * The offending sequence was the following in sym_wakeup_done() of the
  13  * sym53c8xx_2 driver:
  14  *
  15  *      call    sym_ccb_from_dsa, 0
  16  *       movge  %icc, 0, %l0
  17  *      brz,pn  %o0, .LL1303
  18  *       mov    %o0, %l2
  19  *      membar  #LoadLoad
  20  *
  21  * The branch has to be mispredicted for the bug to occur.  Therefore, we put
  22  * the memory barrier explicitly into a "branch always, predicted taken"
  23  * delay slot to avoid the problem case.
  24  */
  25 #define membar_safe(type) \
  26 do {    __asm__ __volatile__("ba,pt     %%xcc, 1f\n\t" \
  27                              " membar   " type "\n" \
  28                              "1:\n" \
  29                              : : : "memory"); \
  30 } while (0)
  31
  32 /* The kernel always executes in TSO memory model these days,
  33  * and furthermore most sparc64 chips implement more stringent
  34  * memory ordering than required by the specifications.
  35  */
  36 #define mb()    membar_safe("#StoreLoad")
  37 #define rmb()   __asm__ __volatile__("":::"memory")
  38 #define wmb()   __asm__ __volatile__("":::"memory")
  39
  40 #define __smp_store_release(p, v)                                               \
  41 do {                                                                    \
  42         compiletime_assert_atomic_type(*p);                             \
  43         barrier();                                                      \
  44         WRITE_ONCE(*p, v);                                              \
  45 } while (0)
  46
  47 #define __smp_load_acquire(p)                                           \
  48 ({                                                                      \
  49         typeof(*p) ___p1 = READ_ONCE(*p);                               \
  50         compiletime_assert_atomic_type(*p);                             \
  51         barrier();                                                      \
  52         ___p1;                                                          \
  53 })
  54
  55 #define __smp_mb__before_atomic()       barrier()
  56 #define __smp_mb__after_atomic()        barrier()
  57
  58 #include <asm-generic/barrier.h>
  59
  60 #endif /* !(__SPARC64_BARRIER_H) */