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