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 */
18 static 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
40 static inline unsigned long xchg_u16(volatile u16 *m, unsigned long val)
41 {
42 return __xchg_cmpxchg(m, val, sizeof *m);
43 }
44
45 static 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
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