1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef __ASM_SH_CMPXCHG_XCHG_H
3#define __ASM_SH_CMPXCHG_XCHG_H
4
5/*
6 * Copyright (C) 2016 Red Hat, Inc.
7 * Author: Michael S. Tsirkin <mst@redhat.com>
8 */
9#include <linux/bits.h>
10#include <linux/compiler.h>
11#include <asm/byteorder.h>
12
13/*
14 * Portable implementations of 1 and 2 byte xchg using a 4 byte cmpxchg.
15 * Note: this header isn't self-contained: before including it, __cmpxchg_u32
16 * must be defined first.
17 */
18static inline u32 __xchg_cmpxchg(volatile void *ptr, u32 x, int size)
19{
20	int off = (unsigned long)ptr % sizeof(u32);
21	volatile u32 *p = ptr - off;
22#ifdef __BIG_ENDIAN
23	int bitoff = (sizeof(u32) - size - off) * BITS_PER_BYTE;
24#else
25	int bitoff = off * BITS_PER_BYTE;
26#endif
27	u32 bitmask = ((0x1 << size * BITS_PER_BYTE) - 1) << bitoff;
28	u32 oldv, newv;
29	u32 ret;
30
31	do {
32		oldv = READ_ONCE(*p);
33		ret = (oldv & bitmask) >> bitoff;
34		newv = (oldv & ~bitmask) | (x << bitoff);
35	} while (__cmpxchg_u32(p, oldv, newv) != oldv);
36
37	return ret;
38}
39
40static inline unsigned long xchg_u16(volatile u16 *m, unsigned long val)
41{
42	return __xchg_cmpxchg(m, val, sizeof *m);
43}
44
45static inline unsigned long xchg_u8(volatile u8 *m, unsigned long val)
46{
47	return __xchg_cmpxchg(m, val, sizeof *m);
48}
49
50#endif /* __ASM_SH_CMPXCHG_XCHG_H */
51