arch/powerpc/include/asm/barrier.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu>
   4  */
   5 #ifndef _ASM_POWERPC_BARRIER_H
   6 #define _ASM_POWERPC_BARRIER_H
   7
   8 /*
   9  * Memory barrier.
  10  * The sync instruction guarantees that all memory accesses initiated
  11  * by this processor have been performed (with respect to all other
  12  * mechanisms that access memory).  The eieio instruction is a barrier
  13  * providing an ordering (separately) for (a) cacheable stores and (b)
  14  * loads and stores to non-cacheable memory (e.g. I/O devices).
  15  *
  16  * mb() prevents loads and stores being reordered across this point.
  17  * rmb() prevents loads being reordered across this point.
  18  * wmb() prevents stores being reordered across this point.
  19  * read_barrier_depends() prevents data-dependent loads being reordered
  20  *      across this point (nop on PPC).
  21  *
  22  * *mb() variants without smp_ prefix must order all types of memory
  23  * operations with one another. sync is the only instruction sufficient
  24  * to do this.
  25  *
  26  * For the smp_ barriers, ordering is for cacheable memory operations
  27  * only. We have to use the sync instruction for smp_mb(), since lwsync
  28  * doesn't order loads with respect to previous stores.  Lwsync can be
  29  * used for smp_rmb() and smp_wmb().
  30  *
  31  * However, on CPUs that don't support lwsync, lwsync actually maps to a
  32  * heavy-weight sync, so smp_wmb() can be a lighter-weight eieio.
  33  */
  34 #define mb()   __asm__ __volatile__ ("sync" : : : "memory")
  35 #define rmb()  __asm__ __volatile__ ("sync" : : : "memory")
  36 #define wmb()  __asm__ __volatile__ ("sync" : : : "memory")
  37
  38 /* The sub-arch has lwsync */
  39 #if defined(__powerpc64__) || defined(CONFIG_PPC_E500MC)
  40 #    define SMPWMB      LWSYNC
  41 #else
  42 #    define SMPWMB      eieio
  43 #endif
  44
  45 #define __lwsync()      __asm__ __volatile__ (stringify_in_c(LWSYNC) : : :"memory")
  46 #define dma_rmb()       __lwsync()
  47 #define dma_wmb()       __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
  48
  49 #define __smp_lwsync()  __lwsync()
  50
  51 #define __smp_mb()      mb()
  52 #define __smp_rmb()     __lwsync()
  53 #define __smp_wmb()     __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
  54
  55 /*
  56  * This is a barrier which prevents following instructions from being
  57  * started until the value of the argument x is known.  For example, if
  58  * x is a variable loaded from memory, this prevents following
  59  * instructions from being executed until the load has been performed.
  60  */
  61 #define data_barrier(x) \
  62         asm volatile("twi 0,%0,0; isync" : : "r" (x) : "memory");
  63
  64 #define __smp_store_release(p, v)                                               \
  65 do {                                                                    \
  66         compiletime_assert_atomic_type(*p);                             \
  67         __smp_lwsync();                                                 \
  68         WRITE_ONCE(*p, v);                                              \
  69 } while (0)
  70
  71 #define __smp_load_acquire(p)                                           \
  72 ({                                                                      \
  73         typeof(*p) ___p1 = READ_ONCE(*p);                               \
  74         compiletime_assert_atomic_type(*p);                             \
  75         __smp_lwsync();                                                 \
  76         ___p1;                                                          \
  77 })
  78
  79 #ifdef CONFIG_PPC_BARRIER_NOSPEC
  80 /*
  81  * Prevent execution of subsequent instructions until preceding branches have
  82  * been fully resolved and are no longer executing speculatively.
  83  */
  84 #define barrier_nospec_asm NOSPEC_BARRIER_FIXUP_SECTION; nop
  85
  86 // This also acts as a compiler barrier due to the memory clobber.
  87 #define barrier_nospec() asm (stringify_in_c(barrier_nospec_asm) ::: "memory")
  88
  89 #else /* !CONFIG_PPC_BARRIER_NOSPEC */
  90 #define barrier_nospec_asm
  91 #define barrier_nospec()
  92 #endif /* CONFIG_PPC_BARRIER_NOSPEC */
  93
  94 #include <asm-generic/barrier.h>
  95
  96 #endif /* _ASM_POWERPC_BARRIER_H */