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1337173148
The current implementations of __ndelay and __udelay call a hypervisor service to delay, but the hypervisor service isn't actually implemented very well, and the consensus is that Linux should handle figuring this out natively and not use a hypervisor service. By converting nanoseconds to cycles, and then spinning until the cycle counter reaches the desired cycle, we get several benefits: first, we are sensitive to the actual clock speed; second, we use less power by issuing a slow SPR read once every six cycles while we delay; and third, we properly handle the case of an interrupt by exiting at the target time rather than after some number of cycles. Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
45 lines
1.2 KiB
C
45 lines
1.2 KiB
C
/*
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* Copyright 2010 Tilera Corporation. All Rights Reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation, version 2.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
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* NON INFRINGEMENT. See the GNU General Public License for
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* more details.
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*/
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#include <linux/module.h>
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#include <linux/delay.h>
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#include <linux/thread_info.h>
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#include <asm/timex.h>
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void __udelay(unsigned long usecs)
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{
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if (usecs > ULONG_MAX / 1000) {
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WARN_ON_ONCE(usecs > ULONG_MAX / 1000);
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usecs = ULONG_MAX / 1000;
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}
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__ndelay(usecs * 1000);
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}
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EXPORT_SYMBOL(__udelay);
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void __ndelay(unsigned long nsecs)
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{
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cycles_t target = get_cycles();
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target += ns2cycles(nsecs);
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while (get_cycles() < target)
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cpu_relax();
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}
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EXPORT_SYMBOL(__ndelay);
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void __delay(unsigned long cycles)
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{
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cycles_t target = get_cycles() + cycles;
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while (get_cycles() < target)
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cpu_relax();
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}
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EXPORT_SYMBOL(__delay);
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