xref: /openbmc/linux/kernel/time/test_udelay.c (revision 5b268d8a)
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 
23 static DEFINE_MUTEX(udelay_test_lock);
24 static int udelay_test_usecs;
25 static int udelay_test_iterations = DEFAULT_ITERATIONS;
26 
udelay_test_single(struct seq_file * s,int usecs,uint32_t iters)27 static 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 
udelay_test_show(struct seq_file * s,void * v)67 static 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 
udelay_test_open(struct inode * inode,struct file * file)94 static int udelay_test_open(struct inode *inode, struct file *file)
95 {
96 	return single_open(file, udelay_test_show, inode->i_private);
97 }
98 
udelay_test_write(struct file * file,const char __user * buf,size_t count,loff_t * pos)99 static 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 
128 static 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 
udelay_test_init(void)137 static 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 
147 module_init(udelay_test_init);
148 
udelay_test_exit(void)149 static 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 
156 module_exit(udelay_test_exit);
157 
158 MODULE_AUTHOR("David Riley <davidriley@chromium.org>");
159 MODULE_LICENSE("GPL");
160