linux-imx

// 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");