Linux Kernel  3.7.1
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cmpxchg.h
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1 /*
2  * Generic UP xchg and cmpxchg using interrupt disablement. Does not
3  * support SMP.
4  */
5 
6 #ifndef __ASM_GENERIC_CMPXCHG_H
7 #define __ASM_GENERIC_CMPXCHG_H
8 
9 #ifdef CONFIG_SMP
10 #error "Cannot use generic cmpxchg on SMP"
11 #endif
12 
13 #include <linux/types.h>
14 #include <linux/irqflags.h>
15 
16 #ifndef xchg
17 
18 /*
19  * This function doesn't exist, so you'll get a linker error if
20  * something tries to do an invalidly-sized xchg().
21  */
22 extern void __xchg_called_with_bad_pointer(void);
23 
24 static inline
25 unsigned long __xchg(unsigned long x, volatile void *ptr, int size)
26 {
27  unsigned long ret, flags;
28 
29  switch (size) {
30  case 1:
31 #ifdef __xchg_u8
32  return __xchg_u8(x, ptr);
33 #else
34  local_irq_save(flags);
35  ret = *(volatile u8 *)ptr;
36  *(volatile u8 *)ptr = x;
37  local_irq_restore(flags);
38  return ret;
39 #endif /* __xchg_u8 */
40 
41  case 2:
42 #ifdef __xchg_u16
43  return __xchg_u16(x, ptr);
44 #else
45  local_irq_save(flags);
46  ret = *(volatile u16 *)ptr;
47  *(volatile u16 *)ptr = x;
48  local_irq_restore(flags);
49  return ret;
50 #endif /* __xchg_u16 */
51 
52  case 4:
53 #ifdef __xchg_u32
54  return __xchg_u32(x, ptr);
55 #else
56  local_irq_save(flags);
57  ret = *(volatile u32 *)ptr;
58  *(volatile u32 *)ptr = x;
59  local_irq_restore(flags);
60  return ret;
61 #endif /* __xchg_u32 */
62 
63 #ifdef CONFIG_64BIT
64  case 8:
65 #ifdef __xchg_u64
66  return __xchg_u64(x, ptr);
67 #else
68  local_irq_save(flags);
69  ret = *(volatile u64 *)ptr;
70  *(volatile u64 *)ptr = x;
71  local_irq_restore(flags);
72  return ret;
73 #endif /* __xchg_u64 */
74 #endif /* CONFIG_64BIT */
75 
76  default:
78  return x;
79  }
80 }
81 
82 #define xchg(ptr, x) \
83  ((__typeof__(*(ptr))) __xchg((unsigned long)(x), (ptr), sizeof(*(ptr))))
84 
85 #endif /* xchg */
86 
87 /*
88  * Atomic compare and exchange.
89  *
90  * Do not define __HAVE_ARCH_CMPXCHG because we want to use it to check whether
91  * a cmpxchg primitive faster than repeated local irq save/restore exists.
92  */
94 
95 #define cmpxchg(ptr, o, n) cmpxchg_local((ptr), (o), (n))
96 #define cmpxchg64(ptr, o, n) cmpxchg64_local((ptr), (o), (n))
97 
98 #endif /* __ASM_GENERIC_CMPXCHG_H */