mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-11-25 11:30:54 +07:00
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
|
|
#define _LINUX_DELAY_H
|
|
|
|
/*
|
|
* Copyright (C) 1993 Linus Torvalds
|
|
*
|
|
* Delay routines, using a pre-computed "loops_per_jiffy" value.
|
|
*
|
|
* Please note that ndelay(), udelay() and mdelay() may return early for
|
|
* several reasons:
|
|
* 1. computed loops_per_jiffy too low (due to the time taken to
|
|
* execute the timer interrupt.)
|
|
* 2. cache behaviour affecting the time it takes to execute the
|
|
* loop function.
|
|
* 3. CPU clock rate changes.
|
|
*
|
|
* Please see this thread:
|
|
* http://lists.openwall.net/linux-kernel/2011/01/09/56
|
|
*/
|
|
|
|
#include <linux/kernel.h>
|
|
|
|
extern unsigned long loops_per_jiffy;
|
|
|
|
#include <asm/delay.h>
|
|
|
|
/*
|
|
* Using udelay() for intervals greater than a few milliseconds can
|
|
* risk overflow for high loops_per_jiffy (high bogomips) machines. The
|
|
* mdelay() provides a wrapper to prevent this. For delays greater
|
|
* than MAX_UDELAY_MS milliseconds, the wrapper is used. Architecture
|
|
* specific values can be defined in asm-???/delay.h as an override.
|
|
* The 2nd mdelay() definition ensures GCC will optimize away the
|
|
* while loop for the common cases where n <= MAX_UDELAY_MS -- Paul G.
|
|
*/
|
|
|
|
#ifndef MAX_UDELAY_MS
|
|
#define MAX_UDELAY_MS 5
|
|
#endif
|
|
|
|
#ifndef mdelay
|
|
#define mdelay(n) (\
|
|
(__builtin_constant_p(n) && (n)<=MAX_UDELAY_MS) ? udelay((n)*1000) : \
|
|
({unsigned long __ms=(n); while (__ms--) udelay(1000);}))
|
|
#endif
|
|
|
|
#ifndef ndelay
|
|
static inline void ndelay(unsigned long x)
|
|
{
|
|
udelay(DIV_ROUND_UP(x, 1000));
|
|
}
|
|
#define ndelay(x) ndelay(x)
|
|
#endif
|
|
|
|
extern unsigned long lpj_fine;
|
|
void calibrate_delay(void);
|
|
void msleep(unsigned int msecs);
|
|
unsigned long msleep_interruptible(unsigned int msecs);
|
|
void usleep_range(unsigned long min, unsigned long max);
|
|
|
|
static inline void ssleep(unsigned int seconds)
|
|
{
|
|
msleep(seconds * 1000);
|
|
}
|
|
|
|
#endif /* defined(_LINUX_DELAY_H) */
|