xref: /linux/include/asm-generic/mmiowb.h (revision bd024e82)
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 
mmiowb_set_pending(void)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 
mmiowb_spin_lock(void)43 static inline void mmiowb_spin_lock(void)
44 {
45 	struct mmiowb_state *ms = __mmiowb_state();
46 	ms->nesting_count++;
47 }
48 
mmiowb_spin_unlock(void)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