// SPDX-License-Identifier: GPL-2.0
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/*
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* udelay() test kernel module
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*
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* Test is executed by writing and reading to /sys/kernel/debug/udelay_test
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* Tests are configured by writing: USECS ITERATIONS
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* Tests are executed by reading from the same file.
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* Specifying usecs of 0 or negative values will run multiples tests.
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*
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* Copyright (C) 2014 Google, Inc.
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*/
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#include <linux/debugfs.h>
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#include <linux/delay.h>
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#include <linux/ktime.h>
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#include <linux/module.h>
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#include <linux/uaccess.h>
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#define DEFAULT_ITERATIONS 100
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#define DEBUGFS_FILENAME "udelay_test"
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static DEFINE_MUTEX(udelay_test_lock);
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static struct dentry *udelay_test_debugfs_file;
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static int udelay_test_usecs;
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static int udelay_test_iterations = DEFAULT_ITERATIONS;
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static int udelay_test_single(struct seq_file *s, int usecs, uint32_t iters)
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{
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int min = 0, max = 0, fail_count = 0;
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uint64_t sum = 0;
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uint64_t avg;
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int i;
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/* Allow udelay to be up to 0.5% fast */
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int allowed_error_ns = usecs * 5;
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for (i = 0; i < iters; ++i) {
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s64 kt1, kt2;
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int time_passed;
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kt1 = ktime_get_ns();
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udelay(usecs);
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kt2 = ktime_get_ns();
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time_passed = kt2 - kt1;
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if (i == 0 || time_passed < min)
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min = time_passed;
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if (i == 0 || time_passed > max)
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max = time_passed;
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if ((time_passed + allowed_error_ns) / 1000 < usecs)
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++fail_count;
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WARN_ON(time_passed < 0);
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sum += time_passed;
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}
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avg = sum;
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do_div(avg, iters);
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seq_printf(s, "%d usecs x %d: exp=%d allowed=%d min=%d avg=%lld max=%d",
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usecs, iters, usecs * 1000,
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(usecs * 1000) - allowed_error_ns, min, avg, max);
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if (fail_count)
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seq_printf(s, " FAIL=%d", fail_count);
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seq_puts(s, "\n");
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return 0;
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}
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static int udelay_test_show(struct seq_file *s, void *v)
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{
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int usecs;
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int iters;
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int ret = 0;
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mutex_lock(&udelay_test_lock);
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usecs = udelay_test_usecs;
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iters = udelay_test_iterations;
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mutex_unlock(&udelay_test_lock);
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if (usecs > 0 && iters > 0) {
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return udelay_test_single(s, usecs, iters);
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} else if (usecs == 0) {
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struct timespec64 ts;
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ktime_get_ts64(&ts);
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seq_printf(s, "udelay() test (lpj=%ld kt=%lld.%09ld)\n",
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loops_per_jiffy, (s64)ts.tv_sec, ts.tv_nsec);
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seq_puts(s, "usage:\n");
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seq_puts(s, "echo USECS [ITERS] > " DEBUGFS_FILENAME "\n");
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seq_puts(s, "cat " DEBUGFS_FILENAME "\n");
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}
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return ret;
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}
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static int udelay_test_open(struct inode *inode, struct file *file)
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{
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return single_open(file, udelay_test_show, inode->i_private);
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}
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static ssize_t udelay_test_write(struct file *file, const char __user *buf,
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size_t count, loff_t *pos)
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{
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char lbuf[32];
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int ret;
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int usecs;
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int iters;
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if (count >= sizeof(lbuf))
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return -EINVAL;
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if (copy_from_user(lbuf, buf, count))
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return -EFAULT;
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lbuf[count] = '\0';
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ret = sscanf(lbuf, "%d %d", &usecs, &iters);
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if (ret < 1)
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return -EINVAL;
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else if (ret < 2)
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iters = DEFAULT_ITERATIONS;
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mutex_lock(&udelay_test_lock);
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udelay_test_usecs = usecs;
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udelay_test_iterations = iters;
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mutex_unlock(&udelay_test_lock);
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return count;
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}
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static const struct file_operations udelay_test_debugfs_ops = {
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.owner = THIS_MODULE,
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.open = udelay_test_open,
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.read = seq_read,
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.write = udelay_test_write,
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.llseek = seq_lseek,
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.release = single_release,
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};
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static int __init udelay_test_init(void)
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{
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mutex_lock(&udelay_test_lock);
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udelay_test_debugfs_file = debugfs_create_file(DEBUGFS_FILENAME,
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S_IRUSR, NULL, NULL, &udelay_test_debugfs_ops);
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mutex_unlock(&udelay_test_lock);
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return 0;
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}
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module_init(udelay_test_init);
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static void __exit udelay_test_exit(void)
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{
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mutex_lock(&udelay_test_lock);
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debugfs_remove(udelay_test_debugfs_file);
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mutex_unlock(&udelay_test_lock);
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}
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module_exit(udelay_test_exit);
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MODULE_AUTHOR("David Riley <davidriley@chromium.org>");
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MODULE_LICENSE("GPL");
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