1/* SPDX-License-Identifier: GPL-2.0 */
 2/*
 3 * Copyright (C) 2019 Google LLC.
 4 */
 5#ifndef __ASM_RWONCE_H
 6#define __ASM_RWONCE_H
 7
 8#ifdef CONFIG_SMP
 9
10#include <asm/barrier.h>
11
12/*
13 * Alpha is apparently daft enough to reorder address-dependent loads
14 * on some CPU implementations. Knock some common sense into it with
15 * a memory barrier in READ_ONCE().
16 *
17 * For the curious, more information about this unusual reordering is
18 * available in chapter 15 of the "perfbook":
19 *
20 *  https://kernel.org/pub/linux/kernel/people/paulmck/perfbook/perfbook.html
21 *
22 */
23#define __READ_ONCE(x)							\
24({									\
25	__unqual_scalar_typeof(x) __x =					\
26		(*(volatile typeof(__x) *)(&(x)));			\
27	mb();								\
28	(typeof(x))__x;							\
29})
30
31#endif /* CONFIG_SMP */
32
33#include <asm-generic/rwonce.h>
34
35#endif /* __ASM_RWONCE_H */