/*
 * Activity LED trigger
 *
 * Copyright (C) 2017 Willy Tarreau <w@1wt.eu>
 * Partially based on Atsushi Nemoto's ledtrig-heartbeat.c.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/kernel_stat.h>
#include <linux/leds.h>
#include <linux/module.h>
#include <linux/reboot.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/timer.h>
#include "../leds.h"

static int panic_detected;

struct activity_data {
        struct timer_list timer;
        struct led_classdev *led_cdev;
        u64 last_used;
        u64 last_boot;
        int time_left;
        int state;
        int invert;
};

static void led_activity_function(struct timer_list *t)
{
        struct activity_data *activity_data = from_timer(activity_data, t,
                                                         timer);
        struct led_classdev *led_cdev = activity_data->led_cdev;
        unsigned int target;
        unsigned int usage;
        int delay;
        u64 curr_used;
        u64 curr_boot;
        s32 diff_used;
        s32 diff_boot;
        int cpus;
        int i;

        if (test_and_clear_bit(LED_BLINK_BRIGHTNESS_CHANGE, &led_cdev->work_flags))
                led_cdev->blink_brightness = led_cdev->new_blink_brightness;

        if (unlikely(panic_detected)) {
                /* full brightness in case of panic */
                led_set_brightness_nosleep(led_cdev, led_cdev->blink_brightness);
                return;
        }

        cpus = 0;
        curr_used = 0;

        for_each_possible_cpu(i) {
                curr_used += kcpustat_cpu(i).cpustat[CPUTIME_USER]
                          +  kcpustat_cpu(i).cpustat[CPUTIME_NICE]
                          +  kcpustat_cpu(i).cpustat[CPUTIME_SYSTEM]
                          +  kcpustat_cpu(i).cpustat[CPUTIME_SOFTIRQ]
                          +  kcpustat_cpu(i).cpustat[CPUTIME_IRQ];
                cpus++;
        }

        /* We come here every 100ms in the worst case, so that's 100M ns of
         * cumulated time. By dividing by 2^16, we get the time resolution
         * down to 16us, ensuring we won't overflow 32-bit computations below
         * even up to 3k CPUs, while keeping divides cheap on smaller systems.
         */
        curr_boot = ktime_get_boot_ns() * cpus;
        diff_boot = (curr_boot - activity_data->last_boot) >> 16;
        diff_used = (curr_used - activity_data->last_used) >> 16;
        activity_data->last_boot = curr_boot;
        activity_data->last_used = curr_used;

        if (diff_boot <= 0 || diff_used < 0)
                usage = 0;
        else if (diff_used >= diff_boot)
                usage = 100;
        else
                usage = 100 * diff_used / diff_boot;

        /*
         * Now we know the total boot_time multiplied by the number of CPUs, and
         * the total idle+wait time for all CPUs. We'll compare how they evolved
         * since last call. The % of overall CPU usage is :
         *
         *      1 - delta_idle / delta_boot
         *
         * What we want is that when the CPU usage is zero, the LED must blink
         * slowly with very faint flashes that are detectable but not disturbing
         * (typically 10ms every second, or 10ms ON, 990ms OFF). Then we want
         * blinking frequency to increase up to the point where the load is
         * enough to saturate one core in multi-core systems or 50% in single
         * core systems. At this point it should reach 10 Hz with a 10/90 duty
         * cycle (10ms ON, 90ms OFF). After this point, the blinking frequency
         * remains stable (10 Hz) and only the duty cycle increases to report
         * the activity, up to the point where we have 90ms ON, 10ms OFF when
         * all cores are saturated. It's important that the LED never stays in
         * a steady state so that it's easy to distinguish an idle or saturated
         * machine from a hung one.
         *
         * This gives us :
         *   - a target CPU usage of min(50%, 100%/#CPU) for a 10% duty cycle
         *     (10ms ON, 90ms OFF)
         *   - below target :
         *      ON_ms  = 10
         *      OFF_ms = 90 + (1 - usage/target) * 900
         *   - above target :
         *      ON_ms  = 10 + (usage-target)/(100%-target) * 80
         *      OFF_ms = 90 - (usage-target)/(100%-target) * 80
         *
         * In order to keep a good responsiveness, we cap the sleep time to
         * 100 ms and keep track of the sleep time left. This allows us to
         * quickly change it if needed.
         */

        activity_data->time_left -= 100;
        if (activity_data->time_left <= 0) {
                activity_data->time_left = 0;
                activity_data->state = !activity_data->state;
                led_set_brightness_nosleep(led_cdev,
                        (activity_data->state ^ activity_data->invert) ?
                        led_cdev->blink_brightness : LED_OFF);
        }

        target = (cpus > 1) ? (100 / cpus) : 50;

        if (usage < target)
                delay = activity_data->state ?
                        10 :                        /* ON  */
                        990 - 900 * usage / target; /* OFF */
        else
                delay = activity_data->state ?
                        10 + 80 * (usage - target) / (100 - target) : /* ON  */
                        90 - 80 * (usage - target) / (100 - target);  /* OFF */


        if (!activity_data->time_left || delay <= activity_data->time_left)
                activity_data->time_left = delay;

        delay = min_t(int, activity_data->time_left, 100);
        mod_timer(&activity_data->timer, jiffies + msecs_to_jiffies(delay));
}

static ssize_t led_invert_show(struct device *dev,
                               struct device_attribute *attr, char *buf)
{
        struct activity_data *activity_data = led_trigger_get_drvdata(dev);

        return sprintf(buf, "%u\n", activity_data->invert);
}

static ssize_t led_invert_store(struct device *dev,
                                struct device_attribute *attr,
                                const char *buf, size_t size)
{
        struct activity_data *activity_data = led_trigger_get_drvdata(dev);
        unsigned long state;
        int ret;

        ret = kstrtoul(buf, 0, &state);
        if (ret)
                return ret;

        activity_data->invert = !!state;

        return size;
}

static DEVICE_ATTR(invert, 0644, led_invert_show, led_invert_store);

static struct attribute *activity_led_attrs[] = {
        &dev_attr_invert.attr,
        NULL
};
ATTRIBUTE_GROUPS(activity_led);

static int activity_activate(struct led_classdev *led_cdev)
{
        struct activity_data *activity_data;

        activity_data = kzalloc(sizeof(*activity_data), GFP_KERNEL);
        if (!activity_data)
                return -ENOMEM;

        led_set_trigger_data(led_cdev, activity_data);

        activity_data->led_cdev = led_cdev;
        timer_setup(&activity_data->timer, led_activity_function, 0);
        if (!led_cdev->blink_brightness)
                led_cdev->blink_brightness = led_cdev->max_brightness;
        led_activity_function(&activity_data->timer);
        set_bit(LED_BLINK_SW, &led_cdev->work_flags);

        return 0;
}

static void activity_deactivate(struct led_classdev *led_cdev)
{
        struct activity_data *activity_data = led_get_trigger_data(led_cdev);

        del_timer_sync(&activity_data->timer);
        kfree(activity_data);
        clear_bit(LED_BLINK_SW, &led_cdev->work_flags);
}

static struct led_trigger activity_led_trigger = {
        .name       = "activity",
        .activate   = activity_activate,
        .deactivate = activity_deactivate,
        .groups     = activity_led_groups,
};

static int activity_reboot_notifier(struct notifier_block *nb,
                                    unsigned long code, void *unused)
{
        led_trigger_unregister(&activity_led_trigger);
        return NOTIFY_DONE;
}

static int activity_panic_notifier(struct notifier_block *nb,
                                   unsigned long code, void *unused)
{
        panic_detected = 1;
        return NOTIFY_DONE;
}

static struct notifier_block activity_reboot_nb = {
        .notifier_call = activity_reboot_notifier,
};

static struct notifier_block activity_panic_nb = {
        .notifier_call = activity_panic_notifier,
};

static int __init activity_init(void)
{
        int rc = led_trigger_register(&activity_led_trigger);

        if (!rc) {
                atomic_notifier_chain_register(&panic_notifier_list,
                                               &activity_panic_nb);
                register_reboot_notifier(&activity_reboot_nb);
        }
        return rc;
}

static void __exit activity_exit(void)
{
        unregister_reboot_notifier(&activity_reboot_nb);
        atomic_notifier_chain_unregister(&panic_notifier_list,
                                         &activity_panic_nb);
        led_trigger_unregister(&activity_led_trigger);
}

module_init(activity_init);
module_exit(activity_exit);

MODULE_AUTHOR("Willy Tarreau <w@1wt.eu>");
MODULE_DESCRIPTION("Activity LED trigger");
MODULE_LICENSE("GPL v2");