blob: 7e893ae0f10edca35bae5796cebe7f87cdc6be5c (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
|
// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2012 Regents of the University of California
*/
#include <linux/delay.h>
#include <linux/param.h>
#include <linux/timex.h>
#include <linux/export.h>
/*
* This is copies from arch/arm/include/asm/delay.h
*
* 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_US 2000
#define MAX_UDELAY_HZ 1000
#define UDELAY_MULT (2147UL * HZ + 483648UL * HZ / 1000000UL)
#define UDELAY_SHIFT 31
#if HZ > MAX_UDELAY_HZ
#error "HZ > MAX_UDELAY_HZ"
#endif
/*
* RISC-V supports both UDELAY and NDELAY. This is largely the same as above,
* but with different constants. I added 10 bits to the shift to get this, but
* the result is that I need a 64-bit multiply, which is slow on 32-bit
* platforms.
*
* NDELAY_MULT = 2^41 * HZ / 1000000000
* = (2^41 / 1000000000) * HZ
* = 2199.02325555 * HZ
* = 2199 * HZ + 23255550 * HZ / 1000000000
*
* The maximum here is to avoid 64-bit overflow, but it isn't checked as it
* won't happen.
*/
#define MAX_NDELAY_NS (1ULL << 42)
#define MAX_NDELAY_HZ MAX_UDELAY_HZ
#define NDELAY_MULT ((unsigned long long)(2199ULL * HZ + 23255550ULL * HZ / 1000000000ULL))
#define NDELAY_SHIFT 41
#if HZ > MAX_NDELAY_HZ
#error "HZ > MAX_NDELAY_HZ"
#endif
void __delay(unsigned long cycles)
{
u64 t0 = get_cycles();
while ((unsigned long)(get_cycles() - t0) < cycles)
cpu_relax();
}
EXPORT_SYMBOL(__delay);
void udelay(unsigned long usecs)
{
unsigned long ucycles = usecs * lpj_fine * UDELAY_MULT;
if (unlikely(usecs > MAX_UDELAY_US)) {
__delay((u64)usecs * riscv_timebase / 1000000ULL);
return;
}
__delay(ucycles >> UDELAY_SHIFT);
}
EXPORT_SYMBOL(udelay);
void ndelay(unsigned long nsecs)
{
/*
* This doesn't bother checking for overflow, as it won't happen (it's
* an hour) of delay.
*/
unsigned long long ncycles = nsecs * lpj_fine * NDELAY_MULT;
__delay(ncycles >> NDELAY_SHIFT);
}
EXPORT_SYMBOL(ndelay);
|
