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