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f36eb17141
A lot of commonly used functions for inserting a sleep or delay lack a proper function description. Add function descriptions to all of them to have important information in a central place close to the code. No functional change. Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Link: https://lore.kernel.org/all/20241014-devel-anna-maria-b4-timers-flseep-v3-5-dc8b907cb62f@linutronix.de
79 lines
2.5 KiB
C
79 lines
2.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __ASM_GENERIC_DELAY_H
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#define __ASM_GENERIC_DELAY_H
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/* Undefined functions to get compile-time errors */
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extern void __bad_udelay(void);
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extern void __bad_ndelay(void);
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extern void __udelay(unsigned long usecs);
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extern void __ndelay(unsigned long nsecs);
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extern void __const_udelay(unsigned long xloops);
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extern void __delay(unsigned long loops);
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/*
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* Implementation details:
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*
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* * The weird n/20000 thing suppresses a "comparison is always false due to
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* limited range of data type" warning with non-const 8-bit arguments.
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* * 0x10c7 is 2**32 / 1000000 (rounded up) -> udelay
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* * 0x5 is 2**32 / 1000000000 (rounded up) -> ndelay
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*/
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/**
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* udelay - Inserting a delay based on microseconds with busy waiting
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* @usec: requested delay in microseconds
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*
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* When delaying in an atomic context ndelay(), udelay() and mdelay() are the
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* only valid variants of delaying/sleeping to go with.
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*
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* When inserting delays in non atomic context which are shorter than the time
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* which is required to queue e.g. an hrtimer and to enter then the scheduler,
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* it is also valuable to use udelay(). But it is not simple to specify a
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* generic threshold for this which will fit for all systems. An approximation
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* is a threshold for all delays up to 10 microseconds.
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*
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* When having a delay which is larger than the architecture specific
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* %MAX_UDELAY_MS value, please make sure mdelay() is used. Otherwise a overflow
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* risk is given.
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*
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* Please note that ndelay(), udelay() and mdelay() may return early for several
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* reasons (https://lists.openwall.net/linux-kernel/2011/01/09/56):
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*
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* #. computed loops_per_jiffy too low (due to the time taken to execute the
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* timer interrupt.)
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* #. cache behaviour affecting the time it takes to execute the loop function.
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* #. CPU clock rate changes.
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*/
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#define udelay(n) \
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({ \
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if (__builtin_constant_p(n)) { \
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if ((n) / 20000 >= 1) \
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__bad_udelay(); \
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else \
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__const_udelay((n) * 0x10c7ul); \
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} else { \
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__udelay(n); \
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} \
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})
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/**
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* ndelay - Inserting a delay based on nanoseconds with busy waiting
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* @nsec: requested delay in nanoseconds
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*
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* See udelay() for basic information about ndelay() and it's variants.
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*/
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#define ndelay(n) \
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({ \
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if (__builtin_constant_p(n)) { \
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if ((n) / 20000 >= 1) \
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__bad_ndelay(); \
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else \
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__const_udelay((n) * 5ul); \
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} else { \
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__ndelay(n); \
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} \
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})
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#endif /* __ASM_GENERIC_DELAY_H */
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