Viewing file:  delay.h (2.83 KB) -rw-r--r--
Select action/file-type:
 (+) |  (+) |  (+) | Code (+) | Session (+) |  (+) | SDB (+) |  (+) |  (+) |  (+) |  (+) |  (+) |
/* SPDX-License-Identifier: GPL-2.0 */
/*
* Copyright (C) 1995-2004 Russell King
*
* Delay routines, using a pre-computed "loops_per_second" value.
*/
#ifndef __ASM_ARM_DELAY_H
#define __ASM_ARM_DELAY_H
#include <asm/memory.h>
#include <asm/param.h> /* HZ */
/*
* Loop (or tick) based delay:
*
* loops = loops_per_jiffy * jiffies_per_sec * delay_us / us_per_sec
*
* where:
*
* jiffies_per_sec = HZ
* us_per_sec = 1000000
*
* Therefore the constant part is HZ / 1000000 which is a small
* fractional number. To make this usable with integer math, we
* scale up this constant by 2^31, perform the actual multiplication,
* and scale the result back down by 2^31 with a simple shift:
*
* loops = (loops_per_jiffy * delay_us * UDELAY_MULT) >> 31
*
* where:
*
* UDELAY_MULT = 2^31 * HZ / 1000000
* = (2^31 / 1000000) * HZ
* = 2147.483648 * HZ
* = 2147 * HZ + 483648 * HZ / 1000000
*
* 31 is the biggest scale shift value that won't overflow 32 bits for
* delay_us * UDELAY_MULT assuming HZ <= 1000 and delay_us <= 2000.
*/
#define MAX_UDELAY_MS 2
#define UDELAY_MULT UL(2147 * HZ + 483648 * HZ / 1000000)
#define UDELAY_SHIFT 31
#ifndef __ASSEMBLY__
struct delay_timer {
unsigned long (*read_current_timer)(void);
unsigned long freq;
};
extern struct arm_delay_ops {
void (*delay)(unsigned long);
void (*const_udelay)(unsigned long);
void (*udelay)(unsigned long);
unsigned long ticks_per_jiffy;
} arm_delay_ops;
#define __delay(n) arm_delay_ops.delay(n)
/*
* This function intentionally does not exist; if you see references to
* it, it means that you're calling udelay() with an out of range value.
*
* With currently imposed limits, this means that we support a max delay
* of 2000us. Further limits: HZ<=1000
*/
extern void __bad_udelay(void);
/*
* division by multiplication: you don't have to worry about
* loss of precision.
*
* Use only for very small delays ( < 2 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)
*/
#define __udelay(n) arm_delay_ops.udelay(n)
#define __const_udelay(n) arm_delay_ops.const_udelay(n)
#define udelay(n) \
(__builtin_constant_p(n) ? \
((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() : \
__const_udelay((n) * UDELAY_MULT)) : \
__udelay(n))
/* Loop-based definitions for assembly code. */
extern void __loop_delay(unsigned long loops);
extern void __loop_udelay(unsigned long usecs);
extern void __loop_const_udelay(unsigned long);
/* Delay-loop timer registration. */
#define ARCH_HAS_READ_CURRENT_TIMER
extern void register_current_timer_delay(const struct delay_timer *timer);
#endif /* __ASSEMBLY__ */
#endif /* defined(_ARM_DELAY_H) */
|