arch/alpha/lib/udelay.c

Source file repositories/reference/linux-study-clean/arch/alpha/lib/udelay.c

File Facts

System
Linux kernel
Corpus path
arch/alpha/lib/udelay.c
Extension
.c
Size
1179 bytes
Lines
57
Domain
Architecture Layer
Bucket
arch/alpha
Inferred role
Architecture Layer: exported/initcall integration point
Status
integration implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 1993, 2000 Linus Torvalds
 *
 * Delay routines, using a pre-computed "loops_per_jiffy" value.
 */

#include <linux/module.h>
#include <linux/sched.h> /* for udelay's use of smp_processor_id */
#include <asm/param.h>
#include <asm/smp.h>
#include <linux/delay.h>

/*
 * Use only for very small delays (< 1 msec). 
 *
 * The active part of our cycle counter is only 32-bits wide, and
 * we're treating the difference between two marks as signed.  On
 * a 1GHz box, that's about 2 seconds.
 */

void
__delay(int loops)
{
	int tmp;
	__asm__ __volatile__(
		"	rpcc %0\n"
		"	addl %1,%0,%1\n"
		"1:	rpcc %0\n"
		"	subl %1,%0,%0\n"
		"	bgt %0,1b"
		: "=&r" (tmp), "=r" (loops) : "1"(loops));
}
EXPORT_SYMBOL(__delay);

#ifdef CONFIG_SMP
#define LPJ	 cpu_data[smp_processor_id()].loops_per_jiffy
#else
#define LPJ	 loops_per_jiffy
#endif

void
udelay(unsigned long usecs)
{
	usecs *= (((unsigned long)HZ << 32) / 1000000) * LPJ;
	__delay((long)usecs >> 32);
}
EXPORT_SYMBOL(udelay);

void
ndelay(unsigned long nsecs)
{
	nsecs *= (((unsigned long)HZ << 32) / 1000000000) * LPJ;
	__delay((long)nsecs >> 32);
}
EXPORT_SYMBOL(ndelay);

Annotation

Implementation Notes