LXR linux/include/asm-generic/mmiowb.h

   1/* SPDX-License-Identifier: GPL-2.0 */
   2#ifndef __ASM_GENERIC_MMIOWB_H
   3#define __ASM_GENERIC_MMIOWB_H
   4
   5/*
   6 * Generic implementation of mmiowb() tracking for spinlocks.
   7 *
   8 * If your architecture doesn't ensure that writes to an I/O peripheral
   9 * within two spinlocked sections on two different CPUs are seen by the
  10 * peripheral in the order corresponding to the lock handover, then you
  11 * need to follow these FIVE easy steps:
  12 *
  13 *      1. Implement mmiowb() (and arch_mmiowb_state() if you're fancy)
  14 *         in asm/mmiowb.h, then #include this file
  15 *      2. Ensure your I/O write accessors call mmiowb_set_pending()
  16 *      3. Select ARCH_HAS_MMIOWB
  17 *      4. Untangle the resulting mess of header files
  18 *      5. Complain to your architects
  19 */
  20#ifdef CONFIG_MMIOWB
  21
  22#include <linux/compiler.h>
  23#include <asm-generic/mmiowb_types.h>
  24
  25#ifndef arch_mmiowb_state
  26#include <asm/percpu.h>
  27#include <asm/smp.h>
  28
  29DECLARE_PER_CPU(struct mmiowb_state, __mmiowb_state);
  30#define __mmiowb_state()        this_cpu_ptr(&__mmiowb_state)
  31#else
  32#define __mmiowb_state()        arch_mmiowb_state()
  33#endif  /* arch_mmiowb_state */
  34
  35static inline void mmiowb_set_pending(void)
  36{
  37        struct mmiowb_state *ms = __mmiowb_state();
  38        ms->mmiowb_pending = ms->nesting_count;
  39}
  40
  41static inline void mmiowb_spin_lock(void)
  42{
  43        struct mmiowb_state *ms = __mmiowb_state();
  44        ms->nesting_count++;
  45}
  46
  47static inline void mmiowb_spin_unlock(void)
  48{
  49        struct mmiowb_state *ms = __mmiowb_state();
  50
  51        if (unlikely(ms->mmiowb_pending)) {
  52                ms->mmiowb_pending = 0;
  53                mmiowb();
  54        }
  55
  56        ms->nesting_count--;
  57}
  58#else
  59#define mmiowb_set_pending()            do { } while (0)
  60#define mmiowb_spin_lock()              do { } while (0)
  61#define mmiowb_spin_unlock()            do { } while (0)
  62#endif  /* CONFIG_MMIOWB */
  63#endif  /* __ASM_GENERIC_MMIOWB_H */
  64