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Linux/include/asm-generic/mmiowb.h

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  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 */
 66 

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