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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