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[ARM] 3980/1: extend the ARM Versatile sched_clock implementation from 32 to 63 bit
period This provides a 63 bit clock counter guaranteed to be monotonic over a period of 35583 days instead of a clock wrap every 179 seconds, as long as sched_clock() is called at least once every 89 seconds. This should not be a problem in practice, although a kernel timer could be scheduled every 80 seconds for example simply to call sched_clock() making sure top bits are always synchronized if need be. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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1 changed files with 10 additions and 4 deletions
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@ -27,6 +27,7 @@
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#include <linux/amba/bus.h>
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#include <linux/amba/clcd.h>
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#include <asm/cnt32_to_63.h>
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#include <asm/system.h>
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#include <asm/hardware.h>
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#include <asm/io.h>
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@ -228,14 +229,19 @@ void __init versatile_map_io(void)
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/*
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* This is the Versatile sched_clock implementation. This has
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* a resolution of 41.7ns, and a maximum value of about 179s.
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* a resolution of 41.7ns, and a maximum value of about 35583 days.
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*
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* The return value is guaranteed to be monotonic in that range as
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* long as there is always less than 89 seconds between successive
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* calls to this function.
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*/
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unsigned long long sched_clock(void)
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{
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unsigned long long v;
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unsigned long long v = cnt32_to_63(readl(VERSATILE_REFCOUNTER));
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v = (unsigned long long)readl(VERSATILE_REFCOUNTER) * 125;
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do_div(v, 3);
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/* the <<1 gets rid of the cnt_32_to_63 top bit saving on a bic insn */
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v *= 125<<1;
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do_div(v, 3<<1);
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return v;
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}
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