root/arch/sh/include/asm/cmpxchg-xchg.h

INCLUDED FROM

DEFINITIONS

1. __xchg_cmpxchg
2. xchg_u16
3. xchg_u8

   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 */