1 /*
2 * udelay() test kernel module
3 *
4 * Test is executed by writing and reading to /sys/kernel/debug/udelay_test
5 * Tests are configured by writing: USECS ITERATIONS
6 * Tests are executed by reading from the same file.
7 * Specifying usecs of 0 or negative values will run multiples tests.
8 *
9 * Copyright (C) 2014 Google, Inc.
10 *
11 * This software is licensed under the terms of the GNU General Public
12 * License version 2, as published by the Free Software Foundation, and
13 * may be copied, distributed, and modified under those terms.
14 *
15 * This program is distributed in the hope that it will be useful,
16 * but WITHOUT ANY WARRANTY; without even the implied warranty of
17 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 * GNU General Public License for more details.
19 */
20
21 #include <linux/debugfs.h>
22 #include <linux/delay.h>
23 #include <linux/ktime.h>
24 #include <linux/module.h>
25 #include <linux/uaccess.h>
26
27 #define DEFAULT_ITERATIONS 100
28
29 #define DEBUGFS_FILENAME "udelay_test"
30
31 static DEFINE_MUTEX(udelay_test_lock);
32 static struct dentry *udelay_test_debugfs_file;
33 static int udelay_test_usecs;
34 static int udelay_test_iterations = DEFAULT_ITERATIONS;
35
udelay_test_single(struct seq_file * s,int usecs,uint32_t iters)36 static int udelay_test_single(struct seq_file *s, int usecs, uint32_t iters)
37 {
38 int min = 0, max = 0, fail_count = 0;
39 uint64_t sum = 0;
40 uint64_t avg;
41 int i;
42 /* Allow udelay to be up to 0.5% fast */
43 int allowed_error_ns = usecs * 5;
44
45 for (i = 0; i < iters; ++i) {
46 s64 kt1, kt2;
47 int time_passed;
48
49 kt1 = ktime_get_ns();
50 udelay(usecs);
51 kt2 = ktime_get_ns();
52 time_passed = kt2 - kt1;
53
54 if (i == 0 || time_passed < min)
55 min = time_passed;
56 if (i == 0 || time_passed > max)
57 max = time_passed;
58 if ((time_passed + allowed_error_ns) / 1000 < usecs)
59 ++fail_count;
60 WARN_ON(time_passed < 0);
61 sum += time_passed;
62 }
63
64 avg = sum;
65 do_div(avg, iters);
66 seq_printf(s, "%d usecs x %d: exp=%d allowed=%d min=%d avg=%lld max=%d",
67 usecs, iters, usecs * 1000,
68 (usecs * 1000) - allowed_error_ns, min, avg, max);
69 if (fail_count)
70 seq_printf(s, " FAIL=%d", fail_count);
71 seq_puts(s, "\n");
72
73 return 0;
74 }
75
udelay_test_show(struct seq_file * s,void * v)76 static int udelay_test_show(struct seq_file *s, void *v)
77 {
78 int usecs;
79 int iters;
80 int ret = 0;
81
82 mutex_lock(&udelay_test_lock);
83 usecs = udelay_test_usecs;
84 iters = udelay_test_iterations;
85 mutex_unlock(&udelay_test_lock);
86
87 if (usecs > 0 && iters > 0) {
88 return udelay_test_single(s, usecs, iters);
89 } else if (usecs == 0) {
90 struct timespec64 ts;
91
92 ktime_get_ts64(&ts);
93 seq_printf(s, "udelay() test (lpj=%ld kt=%lld.%09ld)\n",
94 loops_per_jiffy, (s64)ts.tv_sec, ts.tv_nsec);
95 seq_puts(s, "usage:\n");
96 seq_puts(s, "echo USECS [ITERS] > " DEBUGFS_FILENAME "\n");
97 seq_puts(s, "cat " DEBUGFS_FILENAME "\n");
98 }
99
100 return ret;
101 }
102
udelay_test_open(struct inode * inode,struct file * file)103 static int udelay_test_open(struct inode *inode, struct file *file)
104 {
105 return single_open(file, udelay_test_show, inode->i_private);
106 }
107
udelay_test_write(struct file * file,const char __user * buf,size_t count,loff_t * pos)108 static ssize_t udelay_test_write(struct file *file, const char __user *buf,
109 size_t count, loff_t *pos)
110 {
111 char lbuf[32];
112 int ret;
113 int usecs;
114 int iters;
115
116 if (count >= sizeof(lbuf))
117 return -EINVAL;
118
119 if (copy_from_user(lbuf, buf, count))
120 return -EFAULT;
121 lbuf[count] = '\0';
122
123 ret = sscanf(lbuf, "%d %d", &usecs, &iters);
124 if (ret < 1)
125 return -EINVAL;
126 else if (ret < 2)
127 iters = DEFAULT_ITERATIONS;
128
129 mutex_lock(&udelay_test_lock);
130 udelay_test_usecs = usecs;
131 udelay_test_iterations = iters;
132 mutex_unlock(&udelay_test_lock);
133
134 return count;
135 }
136
137 static const struct file_operations udelay_test_debugfs_ops = {
138 .owner = THIS_MODULE,
139 .open = udelay_test_open,
140 .read = seq_read,
141 .write = udelay_test_write,
142 .llseek = seq_lseek,
143 .release = single_release,
144 };
145
udelay_test_init(void)146 static int __init udelay_test_init(void)
147 {
148 mutex_lock(&udelay_test_lock);
149 udelay_test_debugfs_file = debugfs_create_file(DEBUGFS_FILENAME,
150 S_IRUSR, NULL, NULL, &udelay_test_debugfs_ops);
151 mutex_unlock(&udelay_test_lock);
152
153 return 0;
154 }
155
156 module_init(udelay_test_init);
157
udelay_test_exit(void)158 static void __exit udelay_test_exit(void)
159 {
160 mutex_lock(&udelay_test_lock);
161 debugfs_remove(udelay_test_debugfs_file);
162 mutex_unlock(&udelay_test_lock);
163 }
164
165 module_exit(udelay_test_exit);
166
167 MODULE_AUTHOR("David Riley <davidriley@chromium.org>");
168 MODULE_LICENSE("GPL");
169
