/*
 * ladder.c - the residency ladder algorithm
 *
 *  Copyright (C) 2001, 2002 Andy Grover <andrew.grover@intel.com>
 *  Copyright (C) 2001, 2002 Paul Diefenbaugh <paul.s.diefenbaugh@intel.com>
 *  Copyright (C) 2004, 2005 Dominik Brodowski <linux@brodo.de>
 *
 * (C) 2006-2007 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
 *               Shaohua Li <shaohua.li@intel.com>
 *               Adam Belay <abelay@novell.com>
 *
 * This code is licenced under the GPL.
 */

#include <linux/kernel.h>
#include <linux/cpuidle.h>
#include <linux/jiffies.h>
#include <linux/tick.h>

#include <asm/io.h>
#include <linux/uaccess.h>

#define PROMOTION_COUNT 4
#define DEMOTION_COUNT 1

struct ladder_device_state {
        struct {
                u32 promotion_count;
                u32 demotion_count;
                u64 promotion_time_ns;
                u64 demotion_time_ns;
        } threshold;
        struct {
                int promotion_count;
                int demotion_count;
        } stats;
};

struct ladder_device {
        struct ladder_device_state states[CPUIDLE_STATE_MAX];
};

static DEFINE_PER_CPU(struct ladder_device, ladder_devices);

/**
 * ladder_do_selection - prepares private data for a state change
 * @dev: the CPU
 * @ldev: the ladder device
 * @old_idx: the current state index
 * @new_idx: the new target state index
 */
static inline void ladder_do_selection(struct cpuidle_device *dev,
                                       struct ladder_device *ldev,
                                       int old_idx, int new_idx)
{
        ldev->states[old_idx].stats.promotion_count = 0;
        ldev->states[old_idx].stats.demotion_count = 0;
        dev->last_state_idx = new_idx;
}

/**
 * ladder_select_state - selects the next state to enter
 * @drv: cpuidle driver
 * @dev: the CPU
 * @dummy: not used
 */
static int ladder_select_state(struct cpuidle_driver *drv,
                               struct cpuidle_device *dev, bool *dummy)
{
        struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
        struct ladder_device_state *last_state;
        int last_idx = dev->last_state_idx;
        int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
        s64 latency_req = cpuidle_governor_latency_req(dev->cpu);
        s64 last_residency;

        /* Special case when user has set very strict latency requirement */
        if (unlikely(latency_req == 0)) {
                ladder_do_selection(dev, ldev, last_idx, 0);
                return 0;
        }

        last_state = &ldev->states[last_idx];

        last_residency = dev->last_residency_ns - drv->states[last_idx].exit_latency_ns;

        /* consider promotion */
        if (last_idx < drv->state_count - 1 &&
            !dev->states_usage[last_idx + 1].disable &&
            last_residency > last_state->threshold.promotion_time_ns &&
            drv->states[last_idx + 1].exit_latency_ns <= latency_req) {
                last_state->stats.promotion_count++;
                last_state->stats.demotion_count = 0;
                if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) {
                        ladder_do_selection(dev, ldev, last_idx, last_idx + 1);
                        return last_idx + 1;
                }
        }

        /* consider demotion */
        if (last_idx > first_idx &&
            (dev->states_usage[last_idx].disable ||
            drv->states[last_idx].exit_latency_ns > latency_req)) {
                int i;

                for (i = last_idx - 1; i > first_idx; i--) {
                        if (drv->states[i].exit_latency_ns <= latency_req)
                                break;
                }
                ladder_do_selection(dev, ldev, last_idx, i);
                return i;
        }

        if (last_idx > first_idx &&
            last_residency < last_state->threshold.demotion_time_ns) {
                last_state->stats.demotion_count++;
                last_state->stats.promotion_count = 0;
                if (last_state->stats.demotion_count >= last_state->threshold.demotion_count) {
                        ladder_do_selection(dev, ldev, last_idx, last_idx - 1);
                        return last_idx - 1;
                }
        }

        /* otherwise remain at the current state */
        return last_idx;
}

/**
 * ladder_enable_device - setup for the governor
 * @drv: cpuidle driver
 * @dev: the CPU
 */
static int ladder_enable_device(struct cpuidle_driver *drv,
                                struct cpuidle_device *dev)
{
        int i;
        int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
        struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
        struct ladder_device_state *lstate;
        struct cpuidle_state *state;

        dev->last_state_idx = first_idx;

        for (i = first_idx; i < drv->state_count; i++) {
                state = &drv->states[i];
                lstate = &ldev->states[i];

                lstate->stats.promotion_count = 0;
                lstate->stats.demotion_count = 0;

                lstate->threshold.promotion_count = PROMOTION_COUNT;
                lstate->threshold.demotion_count = DEMOTION_COUNT;

                if (i < drv->state_count - 1)
                        lstate->threshold.promotion_time_ns = state->exit_latency_ns;
                if (i > first_idx)
                        lstate->threshold.demotion_time_ns = state->exit_latency_ns;
        }

        return 0;
}

/**
 * ladder_reflect - update the correct last_state_idx
 * @dev: the CPU
 * @index: the index of actual state entered
 */
static void ladder_reflect(struct cpuidle_device *dev, int index)
{
        if (index > 0)
                dev->last_state_idx = index;
}

static struct cpuidle_governor ladder_governor = {
        .name =         "ladder",
        .rating =       10,
        .enable =       ladder_enable_device,
        .select =       ladder_select_state,
        .reflect =      ladder_reflect,
};

/**
 * init_ladder - initializes the governor
 */
static int __init init_ladder(void)
{
        /*
         * When NO_HZ is disabled, or when booting with nohz=off, the ladder
         * governor is better so give it a higher rating than the menu
         * governor.
         */
        if (!tick_nohz_enabled)
                ladder_governor.rating = 25;

        return cpuidle_register_governor(&ladder_governor);
}

postcore_initcall(init_ladder);