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

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