delay.h

来自「linux 内核源代码」· C头文件 代码 · 共 96 行

/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (C) 1994 by Waldorf Electronics
 * Copyright (C) 1995 - 2000, 01, 03 by Ralf Baechle
 * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
 */
#ifndef _ASM_DELAY_H
#define _ASM_DELAY_H

#include <linux/param.h>
#include <linux/smp.h>
#include <asm/compiler.h>

static inline void __delay(unsigned long loops)
{
	if (sizeof(long) == 4)
		__asm__ __volatile__ (
		"	.set	noreorder				\n"
		"	.align	3					\n"
		"1:	bnez	%0, 1b					\n"
		"	subu	%0, 1					\n"
		"	.set	reorder					\n"
		: "=r" (loops)
		: "0" (loops));
	else if (sizeof(long) == 8)
		__asm__ __volatile__ (
		"	.set	noreorder				\n"
		"	.align	3					\n"
		"1:	bnez	%0, 1b					\n"
		"	dsubu	%0, 1					\n"
		"	.set	reorder					\n"
		: "=r" (loops)
		: "0" (loops));
}


/*
 * Division by multiplication: you don't have to worry about
 * loss of precision.
 *
 * Use only for very small delays ( < 1 msec).  Should probably use a
 * lookup table, really, as the multiplications take much too long with
 * short delays.  This is a "reasonable" implementation, though (and the
 * first constant multiplications gets optimized away if the delay is
 * a constant)
 */

static inline void __udelay(unsigned long usecs, unsigned long lpj)
{
	unsigned long lo;

	/*
	 * The rates of 128 is rounded wrongly by the catchall case
	 * for 64-bit.  Excessive precission?  Probably ...
	 */
#if defined(CONFIG_64BIT) && (HZ == 128)
	usecs *= 0x0008637bd05af6c7UL;		/* 2**64 / (1000000 / HZ) */
#elif defined(CONFIG_64BIT)
	usecs *= (0x8000000000000000UL / (500000 / HZ));
#else /* 32-bit junk follows here */
	usecs *= (unsigned long) (((0x8000000000000000ULL / (500000 / HZ)) +
	                           0x80000000ULL) >> 32);
#endif

	if (sizeof(long) == 4)
		__asm__("multu\t%2, %3"
		: "=h" (usecs), "=l" (lo)
		: "r" (usecs), "r" (lpj)
		: GCC_REG_ACCUM);
	else if (sizeof(long) == 8)
		__asm__("dmultu\t%2, %3"
		: "=h" (usecs), "=l" (lo)
		: "r" (usecs), "r" (lpj)
		: GCC_REG_ACCUM);

	__delay(usecs);
}

#define __udelay_val cpu_data[raw_smp_processor_id()].udelay_val

#define udelay(usecs) __udelay((usecs), __udelay_val)

/* make sure "usecs *= ..." in udelay do not overflow. */
#if HZ >= 1000
#define MAX_UDELAY_MS	1
#elif HZ <= 200
#define MAX_UDELAY_MS	5
#else
#define MAX_UDELAY_MS	(1000 / HZ)
#endif

#endif /* _ASM_DELAY_H */