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| -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 @@ -/* - * include/asm/cnt32_to_63.h -- extend a 32-bit counter to 63 bits - * - * Author: Nicolas Pitre - * Created: December 3, 2006 - * Copyright: MontaVista Software, Inc. - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - */ - -#ifndef __INCLUDE_CNT32_TO_63_H__ -#define __INCLUDE_CNT32_TO_63_H__ - -#include <linux/compiler.h> -#include <asm/types.h> -#include <asm/byteorder.h> - -/* - * Prototype: u64 cnt32_to_63(u32 cnt) - * Many hardware clock counters are only 32 bits wide and therefore have - * a relatively short period making wrap-arounds rather frequent. This - * is a problem when implementing sched_clock() for example, where a 64-bit - * non-wrapping monotonic value is expected to be returned. - * - * To overcome that limitation, let's extend a 32-bit counter to 63 bits - * in a completely lock free fashion. Bits 0 to 31 of the clock are provided - * by the hardware while bits 32 to 62 are stored in memory. The top bit in - * memory is used to synchronize with the hardware clock half-period. When - * the top bit of both counters (hardware and in memory) differ then the - * memory is updated with a new value, incrementing it when the hardware - * counter wraps around. - * - * Because a word store in memory is atomic then the incremented value will - * always be in synch with the top bit indicating to any potential concurrent - * reader if the value in memory is up to date or not with regards to the - * needed increment. And any race in updating the value in memory is harmless - * as the same value would simply be stored more than once. - * - * The only restriction for the algorithm to work properly is that this - * code must be executed at least once per each half period of the 32-bit - * counter to properly update the state bit in memory. This is usually not a - * problem in practice, but if it is then a kernel timer could be scheduled - * to manage for this code to be executed often enough. - * - * Note that the top bit (bit 63) in the returned value should be considered - * as garbage. It is not cleared here because callers are likely to use a - * multiplier on the returned value which can get rid of the top bit - * implicitly by making the multiplier even, therefore saving on a runtime - * clear-bit instruction. Otherwise caller must remember to clear the top - * bit explicitly. - */ - -/* this is used only to give gcc a clue about good code generation */ -typedef union { - struct { -#if defined(__LITTLE_ENDIAN) - u32 lo, hi; -#elif defined(__BIG_ENDIAN) - u32 hi, lo; -#endif - }; - u64 val; -} cnt32_to_63_t; - -#define cnt32_to_63(cnt_lo) \ -({ \ - static volatile u32 __m_cnt_hi = 0; \ - cnt32_to_63_t __x; \ - __x.hi = __m_cnt_hi; \ - __x.lo = (cnt_lo); \ - if (unlikely((s32)(__x.hi ^ __x.lo) < 0)) \ - __m_cnt_hi = __x.hi = (__x.hi ^ 0x80000000) + (__x.hi >> 31); \ - __x.val; \ -}) - -#endif |