diff options
Diffstat (limited to 'arch/arm/include/asm/cnt32_to_63.h')
-rw-r--r-- | arch/arm/include/asm/cnt32_to_63.h | 78 |
1 files changed, 0 insertions, 78 deletions
diff --git a/arch/arm/include/asm/cnt32_to_63.h b/arch/arm/include/asm/cnt32_to_63.h deleted file mode 100644 index 480c873fa746..000000000000 --- a/arch/arm/include/asm/cnt32_to_63.h +++ /dev/null | |||
@@ -1,78 +0,0 @@ | |||
1 | /* | ||
2 | * include/asm/cnt32_to_63.h -- extend a 32-bit counter to 63 bits | ||
3 | * | ||
4 | * Author: Nicolas Pitre | ||
5 | * Created: December 3, 2006 | ||
6 | * Copyright: MontaVista Software, Inc. | ||
7 | * | ||
8 | * This program is free software; you can redistribute it and/or modify | ||
9 | * it under the terms of the GNU General Public License version 2 | ||
10 | * as published by the Free Software Foundation. | ||
11 | */ | ||
12 | |||
13 | #ifndef __INCLUDE_CNT32_TO_63_H__ | ||
14 | #define __INCLUDE_CNT32_TO_63_H__ | ||
15 | |||
16 | #include <linux/compiler.h> | ||
17 | #include <asm/types.h> | ||
18 | #include <asm/byteorder.h> | ||
19 | |||
20 | /* | ||
21 | * Prototype: u64 cnt32_to_63(u32 cnt) | ||
22 | * Many hardware clock counters are only 32 bits wide and therefore have | ||
23 | * a relatively short period making wrap-arounds rather frequent. This | ||
24 | * is a problem when implementing sched_clock() for example, where a 64-bit | ||
25 | * non-wrapping monotonic value is expected to be returned. | ||
26 | * | ||
27 | * To overcome that limitation, let's extend a 32-bit counter to 63 bits | ||
28 | * in a completely lock free fashion. Bits 0 to 31 of the clock are provided | ||
29 | * by the hardware while bits 32 to 62 are stored in memory. The top bit in | ||
30 | * memory is used to synchronize with the hardware clock half-period. When | ||
31 | * the top bit of both counters (hardware and in memory) differ then the | ||
32 | * memory is updated with a new value, incrementing it when the hardware | ||
33 | * counter wraps around. | ||
34 | * | ||
35 | * Because a word store in memory is atomic then the incremented value will | ||
36 | * always be in synch with the top bit indicating to any potential concurrent | ||
37 | * reader if the value in memory is up to date or not with regards to the | ||
38 | * needed increment. And any race in updating the value in memory is harmless | ||
39 | * as the same value would simply be stored more than once. | ||
40 | * | ||
41 | * The only restriction for the algorithm to work properly is that this | ||
42 | * code must be executed at least once per each half period of the 32-bit | ||
43 | * counter to properly update the state bit in memory. This is usually not a | ||
44 | * problem in practice, but if it is then a kernel timer could be scheduled | ||
45 | * to manage for this code to be executed often enough. | ||
46 | * | ||
47 | * Note that the top bit (bit 63) in the returned value should be considered | ||
48 | * as garbage. It is not cleared here because callers are likely to use a | ||
49 | * multiplier on the returned value which can get rid of the top bit | ||
50 | * implicitly by making the multiplier even, therefore saving on a runtime | ||
51 | * clear-bit instruction. Otherwise caller must remember to clear the top | ||
52 | * bit explicitly. | ||
53 | */ | ||
54 | |||
55 | /* this is used only to give gcc a clue about good code generation */ | ||
56 | typedef union { | ||
57 | struct { | ||
58 | #if defined(__LITTLE_ENDIAN) | ||
59 | u32 lo, hi; | ||
60 | #elif defined(__BIG_ENDIAN) | ||
61 | u32 hi, lo; | ||
62 | #endif | ||
63 | }; | ||
64 | u64 val; | ||
65 | } cnt32_to_63_t; | ||
66 | |||
67 | #define cnt32_to_63(cnt_lo) \ | ||
68 | ({ \ | ||
69 | static volatile u32 __m_cnt_hi = 0; \ | ||
70 | cnt32_to_63_t __x; \ | ||
71 | __x.hi = __m_cnt_hi; \ | ||
72 | __x.lo = (cnt_lo); \ | ||
73 | if (unlikely((s32)(__x.hi ^ __x.lo) < 0)) \ | ||
74 | __m_cnt_hi = __x.hi = (__x.hi ^ 0x80000000) + (__x.hi >> 31); \ | ||
75 | __x.val; \ | ||
76 | }) | ||
77 | |||
78 | #endif | ||