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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * udelay() test kernel module
4 *
5 * Test is executed by writing and reading to /sys/kernel/debug/udelay_test
6 * Tests are configured by writing: USECS ITERATIONS
7 * Tests are executed by reading from the same file.
8 * Specifying usecs of 0 or negative values will run multiples tests.
9 *
10 * Copyright (C) 2014 Google, Inc.
11 */
12
13#include <linux/debugfs.h>
14#include <linux/delay.h>
15#include <linux/ktime.h>
16#include <linux/module.h>
17#include <linux/uaccess.h>
18
19#define DEFAULT_ITERATIONS 100
20
21#define DEBUGFS_FILENAME "udelay_test"
22
23static DEFINE_MUTEX(udelay_test_lock);
24static int udelay_test_usecs;
25static int udelay_test_iterations = DEFAULT_ITERATIONS;
26
27static int udelay_test_single(struct seq_file *s, int usecs, uint32_t iters)
28{
29 int min = 0, max = 0, fail_count = 0;
30 uint64_t sum = 0;
31 uint64_t avg;
32 int i;
33 /* Allow udelay to be up to 0.5% fast */
34 int allowed_error_ns = usecs * 5;
35
36 for (i = 0; i < iters; ++i) {
37 s64 kt1, kt2;
38 int time_passed;
39
40 kt1 = ktime_get_ns();
41 udelay(usecs);
42 kt2 = ktime_get_ns();
43 time_passed = kt2 - kt1;
44
45 if (i == 0 || time_passed < min)
46 min = time_passed;
47 if (i == 0 || time_passed > max)
48 max = time_passed;
49 if ((time_passed + allowed_error_ns) / 1000 < usecs)
50 ++fail_count;
51 WARN_ON(time_passed < 0);
52 sum += time_passed;
53 }
54
55 avg = sum;
56 do_div(avg, iters);
57 seq_printf(s, "%d usecs x %d: exp=%d allowed=%d min=%d avg=%lld max=%d",
58 usecs, iters, usecs * 1000,
59 (usecs * 1000) - allowed_error_ns, min, avg, max);
60 if (fail_count)
61 seq_printf(s, " FAIL=%d", fail_count);
62 seq_puts(s, "\n");
63
64 return 0;
65}
66
67static int udelay_test_show(struct seq_file *s, void *v)
68{
69 int usecs;
70 int iters;
71 int ret = 0;
72
73 mutex_lock(&udelay_test_lock);
74 usecs = udelay_test_usecs;
75 iters = udelay_test_iterations;
76 mutex_unlock(&udelay_test_lock);
77
78 if (usecs > 0 && iters > 0) {
79 return udelay_test_single(s, usecs, iters);
80 } else if (usecs == 0) {
81 struct timespec64 ts;
82
83 ktime_get_ts64(&ts);
84 seq_printf(s, "udelay() test (lpj=%ld kt=%lld.%09ld)\n",
85 loops_per_jiffy, (s64)ts.tv_sec, ts.tv_nsec);
86 seq_puts(s, "usage:\n");
87 seq_puts(s, "echo USECS [ITERS] > " DEBUGFS_FILENAME "\n");
88 seq_puts(s, "cat " DEBUGFS_FILENAME "\n");
89 }
90
91 return ret;
92}
93
94static int udelay_test_open(struct inode *inode, struct file *file)
95{
96 return single_open(file, udelay_test_show, inode->i_private);
97}
98
99static ssize_t udelay_test_write(struct file *file, const char __user *buf,
100 size_t count, loff_t *pos)
101{
102 char lbuf[32];
103 int ret;
104 int usecs;
105 int iters;
106
107 if (count >= sizeof(lbuf))
108 return -EINVAL;
109
110 if (copy_from_user(lbuf, buf, count))
111 return -EFAULT;
112 lbuf[count] = '\0';
113
114 ret = sscanf(lbuf, "%d %d", &usecs, &iters);
115 if (ret < 1)
116 return -EINVAL;
117 else if (ret < 2)
118 iters = DEFAULT_ITERATIONS;
119
120 mutex_lock(&udelay_test_lock);
121 udelay_test_usecs = usecs;
122 udelay_test_iterations = iters;
123 mutex_unlock(&udelay_test_lock);
124
125 return count;
126}
127
128static const struct file_operations udelay_test_debugfs_ops = {
129 .owner = THIS_MODULE,
130 .open = udelay_test_open,
131 .read = seq_read,
132 .write = udelay_test_write,
133 .llseek = seq_lseek,
134 .release = single_release,
135};
136
137static int __init udelay_test_init(void)
138{
139 mutex_lock(&udelay_test_lock);
140 debugfs_create_file(DEBUGFS_FILENAME, S_IRUSR, NULL, NULL,
141 &udelay_test_debugfs_ops);
142 mutex_unlock(&udelay_test_lock);
143
144 return 0;
145}
146
147module_init(udelay_test_init);
148
149static void __exit udelay_test_exit(void)
150{
151 mutex_lock(&udelay_test_lock);
152 debugfs_lookup_and_remove(DEBUGFS_FILENAME, NULL);
153 mutex_unlock(&udelay_test_lock);
154}
155
156module_exit(udelay_test_exit);
157
158MODULE_DESCRIPTION("udelay test module");
159MODULE_AUTHOR("David Riley <[email protected]>");
160MODULE_LICENSE("GPL");