// SPDX-License-Identifier: GPL-2.0
/*
 * haltpoll.c - haltpoll idle governor
 *
 * Copyright 2019 Red Hat, Inc. and/or its affiliates.
 *
 * This work is licensed under the terms of the GNU GPL, version 2.  See
 * the COPYING file in the top-level directory.
 *
 * Authors: Marcelo Tosatti <mtosatti@redhat.com>
 */

#include <linux/kernel.h>
#include <linux/cpuidle.h>
#include <linux/time.h>
#include <linux/ktime.h>
#include <linux/hrtimer.h>
#include <linux/tick.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/kvm_para.h>
#include <trace/events/power.h>

static unsigned int guest_halt_poll_ns __read_mostly = 200000;
module_param(guest_halt_poll_ns, uint, 0644);

/* division factor to shrink halt_poll_ns */
static unsigned int guest_halt_poll_shrink __read_mostly = 2;
module_param(guest_halt_poll_shrink, uint, 0644);

/* multiplication factor to grow per-cpu poll_limit_ns */
static unsigned int guest_halt_poll_grow __read_mostly = 2;
module_param(guest_halt_poll_grow, uint, 0644);

/* value in us to start growing per-cpu halt_poll_ns */
static unsigned int guest_halt_poll_grow_start __read_mostly = 50000;
module_param(guest_halt_poll_grow_start, uint, 0644);

/* allow shrinking guest halt poll */
static bool guest_halt_poll_allow_shrink __read_mostly = true;
module_param(guest_halt_poll_allow_shrink, bool, 0644);

/**
 * haltpoll_select - selects the next idle state to enter
 * @drv: cpuidle driver containing state data
 * @dev: the CPU
 * @stop_tick: indication on whether or not to stop the tick
 */
static int haltpoll_select(struct cpuidle_driver *drv,
                           struct cpuidle_device *dev,
                           bool *stop_tick)
{
        if (cpuidle_governor_latency_req(dev->cpu) == 0) {
                *stop_tick = false;
                return 0;
        }

        if (dev->poll_limit_ns == 0)
                return 1;

        /* Last state was poll? */
        if (dev->last_state_idx == 0) {
                /* Halt if no event occurred on poll window */
                if (dev->poll_time_limit == true)
                        return 1;

                *stop_tick = false;
                /* Otherwise, poll again */
                return 0;
        }

        *stop_tick = false;
        /* Last state was halt: poll */
        return 0;
}

static void adjust_poll_limit(struct cpuidle_device *dev, u64 block_ns)
{
        unsigned int val;

        /* Grow cpu_halt_poll_us if
         * cpu_halt_poll_us < block_ns < guest_halt_poll_us
         */
        if (block_ns > dev->poll_limit_ns && block_ns <= guest_halt_poll_ns) {
                val = dev->poll_limit_ns * guest_halt_poll_grow;

                if (val < guest_halt_poll_grow_start)
                        val = guest_halt_poll_grow_start;
                if (val > guest_halt_poll_ns)
                        val = guest_halt_poll_ns;

                trace_guest_halt_poll_ns_grow(val, dev->poll_limit_ns);
                dev->poll_limit_ns = val;
        } else if (block_ns > guest_halt_poll_ns &&
                   guest_halt_poll_allow_shrink) {
                unsigned int shrink = guest_halt_poll_shrink;

                val = dev->poll_limit_ns;
                if (shrink == 0) {
                        val = 0;
                } else {
                        val /= shrink;
                        /* Reset value to 0 if shrunk below grow_start */
                        if (val < guest_halt_poll_grow_start)
                                val = 0;
                }

                trace_guest_halt_poll_ns_shrink(val, dev->poll_limit_ns);
                dev->poll_limit_ns = val;
        }
}

/**
 * haltpoll_reflect - update variables and update poll time
 * @dev: the CPU
 * @index: the index of actual entered state
 */
static void haltpoll_reflect(struct cpuidle_device *dev, int index)
{
        dev->last_state_idx = index;

        if (index != 0)
                adjust_poll_limit(dev, dev->last_residency_ns);
}

/**
 * haltpoll_enable_device - scans a CPU's states and does setup
 * @drv: cpuidle driver
 * @dev: the CPU
 */
static int haltpoll_enable_device(struct cpuidle_driver *drv,
                                  struct cpuidle_device *dev)
{
        dev->poll_limit_ns = 0;

        return 0;
}

static struct cpuidle_governor haltpoll_governor = {
        .name =                 "haltpoll",
        .rating =               9,
        .enable =               haltpoll_enable_device,
        .select =               haltpoll_select,
        .reflect =              haltpoll_reflect,
};

static int __init init_haltpoll(void)
{
        if (kvm_para_available())
                return cpuidle_register_governor(&haltpoll_governor);

        return 0;
}

postcore_initcall(init_haltpoll);