linux/arch/x86/lib/delay.c

// SPDX-License-Identifier: GPL-2.0
/*
 *	Precise Delay Loops for i386
 *
 *	Copyright (C) 1993 Linus Torvalds
 *	Copyright (C) 1997 Martin Mares <[email protected]>
 *	Copyright (C) 2008 Jiri Hladky <hladky _dot_ jiri _at_ gmail _dot_ com>
 *
 *	The __delay function must _NOT_ be inlined as its execution time
 *	depends wildly on alignment on many x86 processors. The additional
 *	jump magic is needed to get the timing stable on all the CPU's
 *	we have to worry about.
 */

#include <linux/export.h>
#include <linux/sched.h>
#include <linux/timex.h>
#include <linux/preempt.h>
#include <linux/delay.h>

#include <asm/processor.h>
#include <asm/delay.h>
#include <asm/timer.h>
#include <asm/mwait.h>

#ifdef CONFIG_SMP
# include <asm/smp.h>
#endif

static void delay_loop(u64 __loops);

/*
 * Calibration and selection of the delay mechanism happens only once
 * during boot.
 */
static void (*delay_fn)(u64) __ro_after_init = …;
static void (*delay_halt_fn)(u64 start, u64 cycles) __ro_after_init;

/* simple loop based delay: */
static void delay_loop(u64 __loops)
{ … }

/* TSC based delay: */
static void delay_tsc(u64 cycles)
{ … }

/*
 * On Intel the TPAUSE instruction waits until any of:
 * 1) the TSC counter exceeds the value provided in EDX:EAX
 * 2) global timeout in IA32_UMWAIT_CONTROL is exceeded
 * 3) an external interrupt occurs
 */
static void delay_halt_tpause(u64 start, u64 cycles)
{ … }

/*
 * On some AMD platforms, MWAITX has a configurable 32-bit timer, that
 * counts with TSC frequency. The input value is the number of TSC cycles
 * to wait. MWAITX will also exit when the timer expires.
 */
static void delay_halt_mwaitx(u64 unused, u64 cycles)
{ … }

/*
 * Call a vendor specific function to delay for a given amount of time. Because
 * these functions may return earlier than requested, check for actual elapsed
 * time and call again until done.
 */
static void delay_halt(u64 __cycles)
{ … }

void __init use_tsc_delay(void)
{ … }

void __init use_tpause_delay(void)
{ … }

void use_mwaitx_delay(void)
{ … }

int read_current_timer(unsigned long *timer_val)
{ … }

void __delay(unsigned long loops)
{ … }
EXPORT_SYMBOL(…);

noinline void __const_udelay(unsigned long xloops)
{ … }
EXPORT_SYMBOL(…);

void __udelay(unsigned long usecs)
{ … }
EXPORT_SYMBOL(…);

void __ndelay(unsigned long nsecs)
{ … }
EXPORT_SYMBOL(…);