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