barrier_64.h

Go to the documentation of this file.

#ifndef __SPARC64_BARRIER_H
#define __SPARC64_BARRIER_H

/* These are here in an effort to more fully work around Spitfire Errata
 * #51.  Essentially, if a memory barrier occurs soon after a mispredicted
 * branch, the chip can stop executing instructions until a trap occurs.
 * Therefore, if interrupts are disabled, the chip can hang forever.
 *
 * It used to be believed that the memory barrier had to be right in the
 * delay slot, but a case has been traced recently wherein the memory barrier
 * was one instruction after the branch delay slot and the chip still hung.
 * The offending sequence was the following in sym_wakeup_done() of the
 * sym53c8xx_2 driver:
 *
 *  call    sym_ccb_from_dsa, 0
 *   movge  %icc, 0, %l0
 *  brz,pn  %o0, .LL1303
 *   mov    %o0, %l2
 *  membar  #LoadLoad
 *
 * The branch has to be mispredicted for the bug to occur.  Therefore, we put
 * the memory barrier explicitly into a "branch always, predicted taken"
 * delay slot to avoid the problem case.
 */
#define membar_safe(type) \
do {    __asm__ __volatile__("ba,pt %%xcc, 1f\n\t" \
                 " membar   " type "\n" \
                 "1:\n" \
                 : : : "memory"); \
} while (0)

/* The kernel always executes in TSO memory model these days,
 * and furthermore most sparc64 chips implement more stringent
 * memory ordering than required by the specifications.
 */
#define mb()    membar_safe("#StoreLoad")
#define rmb()   __asm__ __volatile__("":::"memory")
#define wmb()   __asm__ __volatile__("":::"memory")

#define read_barrier_depends()      do { } while(0)
#define set_mb(__var, __value) \
    do { __var = __value; membar_safe("#StoreLoad"); } while(0)

#ifdef CONFIG_SMP
#define smp_mb()    mb()
#define smp_rmb()   rmb()
#define smp_wmb()   wmb()
#else
#define smp_mb()    __asm__ __volatile__("":::"memory")
#define smp_rmb()   __asm__ __volatile__("":::"memory")
#define smp_wmb()   __asm__ __volatile__("":::"memory")
#endif

#define smp_read_barrier_depends()  do { } while(0)

#endif /* !(__SPARC64_BARRIER_H) */