```   1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * Copyright (C) 1995-2004 Russell King
4 *
5 * Delay routines, using a pre-computed "loops_per_second" value.
6 */
7#ifndef __ASM_ARM_DELAY_H
8#define __ASM_ARM_DELAY_H
9
10#include <asm/memory.h>
11#include <asm/param.h>  /* HZ */
12
13/*
14 * Loop (or tick) based delay:
15 *
16 * loops = loops_per_jiffy * jiffies_per_sec * delay_us / us_per_sec
17 *
18 * where:
19 *
20 * jiffies_per_sec = HZ
21 * us_per_sec = 1000000
22 *
23 * Therefore the constant part is HZ / 1000000 which is a small
24 * fractional number. To make this usable with integer math, we
25 * scale up this constant by 2^31, perform the actual multiplication,
26 * and scale the result back down by 2^31 with a simple shift:
27 *
28 * loops = (loops_per_jiffy * delay_us * UDELAY_MULT) >> 31
29 *
30 * where:
31 *
32 * UDELAY_MULT = 2^31 * HZ / 1000000
33 *             = (2^31 / 1000000) * HZ
34 *             = 2147.483648 * HZ
35 *             = 2147 * HZ + 483648 * HZ / 1000000
36 *
37 * 31 is the biggest scale shift value that won't overflow 32 bits for
38 * delay_us * UDELAY_MULT assuming HZ <= 1000 and delay_us <= 2000.
39 */
40#define MAX_UDELAY_MS   2
41#define UDELAY_MULT     UL(2147 * HZ + 483648 * HZ / 1000000)
42#define UDELAY_SHIFT    31
43
44#ifndef __ASSEMBLY__
45
46struct delay_timer {
48        unsigned long freq;
49};
50
51extern struct arm_delay_ops {
52        void (*delay)(unsigned long);
53        void (*const_udelay)(unsigned long);
54        void (*udelay)(unsigned long);
55        unsigned long ticks_per_jiffy;
56} arm_delay_ops;
57
58#define __delay(n)              arm_delay_ops.delay(n)
59
60/*
61 * This function intentionally does not exist; if you see references to
62 * it, it means that you're calling udelay() with an out of range value.
63 *
64 * With currently imposed limits, this means that we support a max delay
65 * of 2000us. Further limits: HZ<=1000
66 */
68
69/*
70 * division by multiplication: you don't have to worry about
71 * loss of precision.
72 *
73 * Use only for very small delays ( < 2 msec).  Should probably use a
74 * lookup table, really, as the multiplications take much too long with
75 * short delays.  This is a "reasonable" implementation, though (and the
76 * first constant multiplications gets optimized away if the delay is
77 * a constant)
78 */
79#define __udelay(n)             arm_delay_ops.udelay(n)
80#define __const_udelay(n)       arm_delay_ops.const_udelay(n)
81
82#define udelay(n)                                                       \
83        (__builtin_constant_p(n) ?                                      \
84          ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() :              \
85                        __const_udelay((n) * UDELAY_MULT)) :            \
86          __udelay(n))
87
88/* Loop-based definitions for assembly code. */
89extern void __loop_delay(unsigned long loops);
90extern void __loop_udelay(unsigned long usecs);
91extern void __loop_const_udelay(unsigned long);
92
93/* Delay-loop timer registration. */