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
  29 DECLARE_PER_CPU(struct mmiowb_state, __mmiowb_state);
  30 #define __mmiowb_state()        raw_cpu_ptr(&__mmiowb_state)
  31 #else
  32 #define __mmiowb_state()        arch_mmiowb_state()
  33 #endif  /* arch_mmiowb_state */
  34
  35 static inline void mmiowb_set_pending(void)
  36 {
  37         struct mmiowb_state *ms = __mmiowb_state();
  38
  39         if (likely(ms->nesting_count))
  40                 ms->mmiowb_pending = ms->nesting_count;
  41 }
  42
  43 static inline void mmiowb_spin_lock(void)
  44 {
  45         struct mmiowb_state *ms = __mmiowb_state();
  46         ms->nesting_count++;
  47 }
  48
  49 static inline void mmiowb_spin_unlock(void)
  50 {
  51         struct mmiowb_state *ms = __mmiowb_state();
  52
  53         if (unlikely(ms->mmiowb_pending)) {
  54                 ms->mmiowb_pending = 0;
  55                 mmiowb();
  56         }
  57
  58         ms->nesting_count--;
  59 }
  60 #else
  61 #define mmiowb_set_pending()            do { } while (0)
  62 #define mmiowb_spin_lock()              do { } while (0)
  63 #define mmiowb_spin_unlock()            do { } while (0)
  64 #endif  /* CONFIG_MMIOWB */
  65 #endif  /* __ASM_GENERIC_MMIOWB_H */