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 read_barrier_depends()          do { } while(0)
  41 #define set_mb(__var, __value) \
  42         do { __var = __value; membar_safe("#StoreLoad"); } while(0)
  43
  44 #ifdef CONFIG_SMP
  45 #define smp_mb()        mb()
  46 #define smp_rmb()       rmb()
  47 #define smp_wmb()       wmb()
  48 #else
  49 #define smp_mb()        __asm__ __volatile__("":::"memory")
  50 #define smp_rmb()       __asm__ __volatile__("":::"memory")
  51 #define smp_wmb()       __asm__ __volatile__("":::"memory")
  52 #endif
  53
  54 #define smp_read_barrier_depends()      do { } while(0)
  55
  56 #endif /* !(__SPARC64_BARRIER_H) */