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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __ASM_GENERIC_DELAY_H
#define __ASM_GENERIC_DELAY_H
#include <linux/math.h>
#include <vdso/time64.h>
/* Undefined functions to get compile-time errors */
extern void __bad_udelay(void);
extern void __bad_ndelay(void);
extern void __udelay(unsigned long usecs);
extern void __ndelay(unsigned long nsecs);
extern void __const_udelay(unsigned long xloops);
extern void __delay(unsigned long loops);
/*
* The microseconds/nanosecond delay multiplicators are used to convert a
* constant microseconds/nanoseconds value to a value which can be used by the
* architectures specific implementation to transform it into loops.
*/
#define UDELAY_CONST_MULT ((unsigned long)DIV_ROUND_UP(1ULL << 32, USEC_PER_SEC))
#define NDELAY_CONST_MULT ((unsigned long)DIV_ROUND_UP(1ULL << 32, NSEC_PER_SEC))
/*
* The maximum constant udelay/ndelay value picked out of thin air to prevent
* too long constant udelays/ndelays.
*/
#define DELAY_CONST_MAX 20000
/**
* udelay - Inserting a delay based on microseconds with busy waiting
* @usec: requested delay in microseconds
*
* When delaying in an atomic context ndelay(), udelay() and mdelay() are the
* only valid variants of delaying/sleeping to go with.
*
* When inserting delays in non atomic context which are shorter than the time
* which is required to queue e.g. an hrtimer and to enter then the scheduler,
* it is also valuable to use udelay(). But it is not simple to specify a
* generic threshold for this which will fit for all systems. An approximation
* is a threshold for all delays up to 10 microseconds.
*
* When having a delay which is larger than the architecture specific
* %MAX_UDELAY_MS value, please make sure mdelay() is used. Otherwise a overflow
* risk is given.
*
* Please note that ndelay(), udelay() and mdelay() may return early for several
* reasons (https://lists.openwall.net/linux-kernel/2011/01/09/56):
*
* #. computed loops_per_jiffy too low (due to the time taken to execute the
* timer interrupt.)
* #. cache behaviour affecting the time it takes to execute the loop function.
* #. CPU clock rate changes.
*/
static __always_inline void udelay(unsigned long usec)
{
if (__builtin_constant_p(usec)) {
if (usec >= DELAY_CONST_MAX)
__bad_udelay();
else
__const_udelay(usec * UDELAY_CONST_MULT);
} else {
__udelay(usec);
}
}
/**
* ndelay - Inserting a delay based on nanoseconds with busy waiting
* @nsec: requested delay in nanoseconds
*
* See udelay() for basic information about ndelay() and it's variants.
*/
static __always_inline void ndelay(unsigned long nsec)
{
if (__builtin_constant_p(nsec)) {
if (nsec >= DELAY_CONST_MAX)
__bad_ndelay();
else
__const_udelay(nsec * NDELAY_CONST_MULT);
} else {
__ndelay(nsec);
}
}
#define ndelay(x) ndelay(x)
#endif /* __ASM_GENERIC_DELAY_H */
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