// SPDX-License-Identifier: GPL-2.0+
/*
 * Unit test for the clocksource watchdog.
 *
 * Copyright (C) 2021 Facebook, Inc.
 *
 * Author: Paul E. McKenney <paulmck@kernel.org>
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/device.h>
#include <linux/clocksource.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
#include <linux/tick.h>
#include <linux/kthread.h>
#include <linux/delay.h>
#include <linux/prandom.h>
#include <linux/cpu.h>

#include "tick-internal.h"

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Clocksource watchdog unit test");
MODULE_AUTHOR("Paul E. McKenney <paulmck@kernel.org>");

static int holdoff = IS_BUILTIN(CONFIG_TEST_CLOCKSOURCE_WATCHDOG) ? 10 : 0;
module_param(holdoff, int, 0444);
MODULE_PARM_DESC(holdoff, "Time to wait to start test (s).");

/* Watchdog kthread's task_struct pointer for debug purposes. */
static struct task_struct *wdtest_task;

static u64 wdtest_jiffies_read(struct clocksource *cs)
{
        return (u64)jiffies;
}

static struct clocksource clocksource_wdtest_jiffies = {
        .name                   = "wdtest-jiffies",
        .rating                 = 1, /* lowest valid rating*/
        .uncertainty_margin     = TICK_NSEC,
        .read                   = wdtest_jiffies_read,
        .mask                   = CLOCKSOURCE_MASK(32),
        .flags                  = CLOCK_SOURCE_MUST_VERIFY,
        .mult                   = TICK_NSEC << JIFFIES_SHIFT, /* details above */
        .shift                  = JIFFIES_SHIFT,
        .max_cycles             = 10,
};

static int wdtest_ktime_read_ndelays;
static bool wdtest_ktime_read_fuzz;

static u64 wdtest_ktime_read(struct clocksource *cs)
{
        int wkrn = READ_ONCE(wdtest_ktime_read_ndelays);
        static int sign = 1;
        u64 ret;

        if (wkrn) {
                udelay(cs->uncertainty_margin / 250);
                WRITE_ONCE(wdtest_ktime_read_ndelays, wkrn - 1);
        }
        ret = ktime_get_real_fast_ns();
        if (READ_ONCE(wdtest_ktime_read_fuzz)) {
                sign = -sign;
                ret = ret + sign * 100 * NSEC_PER_MSEC;
        }
        return ret;
}

static void wdtest_ktime_cs_mark_unstable(struct clocksource *cs)
{
        pr_info("--- Marking %s unstable due to clocksource watchdog.\n", cs->name);
}

#define KTIME_FLAGS (CLOCK_SOURCE_IS_CONTINUOUS | \
                     CLOCK_SOURCE_VALID_FOR_HRES | \
                     CLOCK_SOURCE_MUST_VERIFY | \
                     CLOCK_SOURCE_VERIFY_PERCPU)

static struct clocksource clocksource_wdtest_ktime = {
        .name                   = "wdtest-ktime",
        .rating                 = 300,
        .read                   = wdtest_ktime_read,
        .mask                   = CLOCKSOURCE_MASK(64),
        .flags                  = KTIME_FLAGS,
        .mark_unstable          = wdtest_ktime_cs_mark_unstable,
        .list                   = LIST_HEAD_INIT(clocksource_wdtest_ktime.list),
};

/* Reset the clocksource if needed. */
static void wdtest_ktime_clocksource_reset(void)
{
        if (clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE) {
                clocksource_unregister(&clocksource_wdtest_ktime);
                clocksource_wdtest_ktime.flags = KTIME_FLAGS;
                schedule_timeout_uninterruptible(HZ / 10);
                clocksource_register_khz(&clocksource_wdtest_ktime, 1000 * 1000);
        }
}

/* Run the specified series of watchdog tests. */
static int wdtest_func(void *arg)
{
        unsigned long j1, j2;
        int i, max_retries;
        char *s;

        schedule_timeout_uninterruptible(holdoff * HZ);

        /*
         * Verify that jiffies-like clocksources get the manually
         * specified uncertainty margin.
         */
        pr_info("--- Verify jiffies-like uncertainty margin.\n");
        __clocksource_register(&clocksource_wdtest_jiffies);
        WARN_ON_ONCE(clocksource_wdtest_jiffies.uncertainty_margin != TICK_NSEC);

        j1 = clocksource_wdtest_jiffies.read(&clocksource_wdtest_jiffies);
        schedule_timeout_uninterruptible(HZ);
        j2 = clocksource_wdtest_jiffies.read(&clocksource_wdtest_jiffies);
        WARN_ON_ONCE(j1 == j2);

        clocksource_unregister(&clocksource_wdtest_jiffies);

        /*
         * Verify that tsc-like clocksources are assigned a reasonable
         * uncertainty margin.
         */
        pr_info("--- Verify tsc-like uncertainty margin.\n");
        clocksource_register_khz(&clocksource_wdtest_ktime, 1000 * 1000);
        WARN_ON_ONCE(clocksource_wdtest_ktime.uncertainty_margin < NSEC_PER_USEC);

        j1 = clocksource_wdtest_ktime.read(&clocksource_wdtest_ktime);
        udelay(1);
        j2 = clocksource_wdtest_ktime.read(&clocksource_wdtest_ktime);
        pr_info("--- tsc-like times: %lu - %lu = %lu.\n", j2, j1, j2 - j1);
        WARN_ONCE(time_before(j2, j1 + NSEC_PER_USEC),
                  "Expected at least 1000ns, got %lu.\n", j2 - j1);

        /* Verify tsc-like stability with various numbers of errors injected. */
        max_retries = clocksource_get_max_watchdog_retry();
        for (i = 0; i <= max_retries + 1; i++) {
                if (i <= 1 && i < max_retries)
                        s = "";
                else if (i <= max_retries)
                        s = ", expect message";
                else
                        s = ", expect clock skew";
                pr_info("--- Watchdog with %dx error injection, %d retries%s.\n", i, max_retries, s);
                WRITE_ONCE(wdtest_ktime_read_ndelays, i);
                schedule_timeout_uninterruptible(2 * HZ);
                WARN_ON_ONCE(READ_ONCE(wdtest_ktime_read_ndelays));
                WARN_ON_ONCE((i <= max_retries) !=
                             !(clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE));
                wdtest_ktime_clocksource_reset();
        }

        /* Verify tsc-like stability with clock-value-fuzz error injection. */
        pr_info("--- Watchdog clock-value-fuzz error injection, expect clock skew and per-CPU mismatches.\n");
        WRITE_ONCE(wdtest_ktime_read_fuzz, true);
        schedule_timeout_uninterruptible(2 * HZ);
        WARN_ON_ONCE(!(clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE));
        clocksource_verify_percpu(&clocksource_wdtest_ktime);
        WRITE_ONCE(wdtest_ktime_read_fuzz, false);

        clocksource_unregister(&clocksource_wdtest_ktime);

        pr_info("--- Done with test.\n");
        return 0;
}

static void wdtest_print_module_parms(void)
{
        pr_alert("--- holdoff=%d\n", holdoff);
}

/* Cleanup function. */
static void clocksource_wdtest_cleanup(void)
{
}

static int __init clocksource_wdtest_init(void)
{
        int ret = 0;

        wdtest_print_module_parms();

        /* Create watchdog-test task. */
        wdtest_task = kthread_run(wdtest_func, NULL, "wdtest");
        if (IS_ERR(wdtest_task)) {
                ret = PTR_ERR(wdtest_task);
                pr_warn("%s: Failed to create wdtest kthread.\n", __func__);
                wdtest_task = NULL;
                return ret;
        }

        return 0;
}

module_init(clocksource_wdtest_init);
module_exit(clocksource_wdtest_cleanup);