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1/*
2 * Copyright (C) 2012 Regents of the University of California
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation, version 2.
7 *
8 * This program is distributed in the hope that it will be useful,
9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11 * GNU General Public License for more details.
12 */
13
14#include <linux/delay.h>
15#include <linux/param.h>
16#include <linux/timex.h>
17#include <linux/export.h>
18
19/*
20 * This is copies from arch/arm/include/asm/delay.h
21 *
22 * Loop (or tick) based delay:
23 *
24 * loops = loops_per_jiffy * jiffies_per_sec * delay_us / us_per_sec
25 *
26 * where:
27 *
28 * jiffies_per_sec = HZ
29 * us_per_sec = 1000000
30 *
31 * Therefore the constant part is HZ / 1000000 which is a small
32 * fractional number. To make this usable with integer math, we
33 * scale up this constant by 2^31, perform the actual multiplication,
34 * and scale the result back down by 2^31 with a simple shift:
35 *
36 * loops = (loops_per_jiffy * delay_us * UDELAY_MULT) >> 31
37 *
38 * where:
39 *
40 * UDELAY_MULT = 2^31 * HZ / 1000000
41 * = (2^31 / 1000000) * HZ
42 * = 2147.483648 * HZ
43 * = 2147 * HZ + 483648 * HZ / 1000000
44 *
45 * 31 is the biggest scale shift value that won't overflow 32 bits for
46 * delay_us * UDELAY_MULT assuming HZ <= 1000 and delay_us <= 2000.
47 */
48#define MAX_UDELAY_US 2000
49#define MAX_UDELAY_HZ 1000
50#define UDELAY_MULT (2147UL * HZ + 483648UL * HZ / 1000000UL)
51#define UDELAY_SHIFT 31
52
53#if HZ > MAX_UDELAY_HZ
54#error "HZ > MAX_UDELAY_HZ"
55#endif
56
57/*
58 * RISC-V supports both UDELAY and NDELAY. This is largely the same as above,
59 * but with different constants. I added 10 bits to the shift to get this, but
60 * the result is that I need a 64-bit multiply, which is slow on 32-bit
61 * platforms.
62 *
63 * NDELAY_MULT = 2^41 * HZ / 1000000000
64 * = (2^41 / 1000000000) * HZ
65 * = 2199.02325555 * HZ
66 * = 2199 * HZ + 23255550 * HZ / 1000000000
67 *
68 * The maximum here is to avoid 64-bit overflow, but it isn't checked as it
69 * won't happen.
70 */
71#define MAX_NDELAY_NS (1ULL << 42)
72#define MAX_NDELAY_HZ MAX_UDELAY_HZ
73#define NDELAY_MULT ((unsigned long long)(2199ULL * HZ + 23255550ULL * HZ / 1000000000ULL))
74#define NDELAY_SHIFT 41
75
76#if HZ > MAX_NDELAY_HZ
77#error "HZ > MAX_NDELAY_HZ"
78#endif
79
80void __delay(unsigned long cycles)
81{
82 u64 t0 = get_cycles();
83
84 while ((unsigned long)(get_cycles() - t0) < cycles)
85 cpu_relax();
86}
87EXPORT_SYMBOL(__delay);
88
89void udelay(unsigned long usecs)
90{
91 unsigned long ucycles = usecs * lpj_fine * UDELAY_MULT;
92
93 if (unlikely(usecs > MAX_UDELAY_US)) {
94 __delay((u64)usecs * riscv_timebase / 1000000ULL);
95 return;
96 }
97
98 __delay(ucycles >> UDELAY_SHIFT);
99}
100EXPORT_SYMBOL(udelay);
101
102void ndelay(unsigned long nsecs)
103{
104 /*
105 * This doesn't bother checking for overflow, as it won't happen (it's
106 * an hour) of delay.
107 */
108 unsigned long long ncycles = nsecs * lpj_fine * NDELAY_MULT;
109 __delay(ncycles >> NDELAY_SHIFT);
110}
111EXPORT_SYMBOL(ndelay);
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (C) 2012 Regents of the University of California
4 */
5
6#include <linux/delay.h>
7#include <linux/param.h>
8#include <linux/timex.h>
9#include <linux/export.h>
10
11/*
12 * This is copies from arch/arm/include/asm/delay.h
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_US 2000
41#define MAX_UDELAY_HZ 1000
42#define UDELAY_MULT (2147UL * HZ + 483648UL * HZ / 1000000UL)
43#define UDELAY_SHIFT 31
44
45#if HZ > MAX_UDELAY_HZ
46#error "HZ > MAX_UDELAY_HZ"
47#endif
48
49/*
50 * RISC-V supports both UDELAY and NDELAY. This is largely the same as above,
51 * but with different constants. I added 10 bits to the shift to get this, but
52 * the result is that I need a 64-bit multiply, which is slow on 32-bit
53 * platforms.
54 *
55 * NDELAY_MULT = 2^41 * HZ / 1000000000
56 * = (2^41 / 1000000000) * HZ
57 * = 2199.02325555 * HZ
58 * = 2199 * HZ + 23255550 * HZ / 1000000000
59 *
60 * The maximum here is to avoid 64-bit overflow, but it isn't checked as it
61 * won't happen.
62 */
63#define MAX_NDELAY_NS (1ULL << 42)
64#define MAX_NDELAY_HZ MAX_UDELAY_HZ
65#define NDELAY_MULT ((unsigned long long)(2199ULL * HZ + 23255550ULL * HZ / 1000000000ULL))
66#define NDELAY_SHIFT 41
67
68#if HZ > MAX_NDELAY_HZ
69#error "HZ > MAX_NDELAY_HZ"
70#endif
71
72void __delay(unsigned long cycles)
73{
74 u64 t0 = get_cycles();
75
76 while ((unsigned long)(get_cycles() - t0) < cycles)
77 cpu_relax();
78}
79EXPORT_SYMBOL(__delay);
80
81void udelay(unsigned long usecs)
82{
83 u64 ucycles = (u64)usecs * lpj_fine * UDELAY_MULT;
84 u64 n;
85
86 if (unlikely(usecs > MAX_UDELAY_US)) {
87 n = (u64)usecs * riscv_timebase;
88 do_div(n, 1000000);
89
90 __delay(n);
91 return;
92 }
93
94 __delay(ucycles >> UDELAY_SHIFT);
95}
96EXPORT_SYMBOL(udelay);
97
98void ndelay(unsigned long nsecs)
99{
100 /*
101 * This doesn't bother checking for overflow, as it won't happen (it's
102 * an hour) of delay.
103 */
104 unsigned long long ncycles = nsecs * lpj_fine * NDELAY_MULT;
105 __delay(ncycles >> NDELAY_SHIFT);
106}
107EXPORT_SYMBOL(ndelay);