9f8197980d
There seems to be some misunderstanding that udelay() and friends will always guarantee the specified delay. This is a false understanding. When udelay() is based on CPU cycles, it can return early for many reasons which are detailed by Linus' reply to me in a thread in 2011: http://lists.openwall.net/linux-kernel/2011/01/12/372 However, a udelay test module was created in 2014 which allows udelay() to only be 0.5% fast, which is outside of the CPU-cycles udelay() results I measured back in 2011, which were deemed to be in the "we don't care" region. test_udelay() should be fixed to reflect the real allowable tolerance on udelay(), rather than 0.5%. Cc: David Riley <davidriley@chromium.org> Cc: John Stultz <john.stultz@linaro.org> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk> Signed-off-by: John Stultz <john.stultz@linaro.org>
67 lines
1.8 KiB
C
67 lines
1.8 KiB
C
#ifndef _LINUX_DELAY_H
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#define _LINUX_DELAY_H
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/*
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* Copyright (C) 1993 Linus Torvalds
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*
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* Delay routines, using a pre-computed "loops_per_jiffy" value.
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*
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* Please note that ndelay(), udelay() and mdelay() may return early for
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* several reasons:
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* 1. computed loops_per_jiffy too low (due to the time taken to
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* execute the timer interrupt.)
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* 2. cache behaviour affecting the time it takes to execute the
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* loop function.
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* 3. CPU clock rate changes.
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*
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* Please see this thread:
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* http://lists.openwall.net/linux-kernel/2011/01/09/56
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*/
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#include <linux/kernel.h>
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extern unsigned long loops_per_jiffy;
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#include <asm/delay.h>
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/*
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* Using udelay() for intervals greater than a few milliseconds can
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* risk overflow for high loops_per_jiffy (high bogomips) machines. The
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* mdelay() provides a wrapper to prevent this. For delays greater
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* than MAX_UDELAY_MS milliseconds, the wrapper is used. Architecture
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* specific values can be defined in asm-???/delay.h as an override.
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* The 2nd mdelay() definition ensures GCC will optimize away the
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* while loop for the common cases where n <= MAX_UDELAY_MS -- Paul G.
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*/
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#ifndef MAX_UDELAY_MS
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#define MAX_UDELAY_MS 5
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#endif
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#ifndef mdelay
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#define mdelay(n) (\
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(__builtin_constant_p(n) && (n)<=MAX_UDELAY_MS) ? udelay((n)*1000) : \
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({unsigned long __ms=(n); while (__ms--) udelay(1000);}))
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#endif
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#ifndef ndelay
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static inline void ndelay(unsigned long x)
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{
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udelay(DIV_ROUND_UP(x, 1000));
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}
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#define ndelay(x) ndelay(x)
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#endif
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extern unsigned long lpj_fine;
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void calibrate_delay(void);
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void msleep(unsigned int msecs);
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unsigned long msleep_interruptible(unsigned int msecs);
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void usleep_range(unsigned long min, unsigned long max);
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static inline void ssleep(unsigned int seconds)
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{
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msleep(seconds * 1000);
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}
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#endif /* defined(_LINUX_DELAY_H) */
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