// SPDX-License-Identifier: GPL-2.0
/*
 * cpuidle driver for haltpoll 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/init.h>
#include <linux/cpu.h>
#include <linux/cpuidle.h>
#include <linux/module.h>
#include <linux/sched/idle.h>
#include <linux/kvm_para.h>
#include <linux/cpuidle_haltpoll.h>

static bool force __read_mostly;
module_param(force, bool, 0444);
MODULE_PARM_DESC(force, "Load unconditionally");

static struct cpuidle_device __percpu *haltpoll_cpuidle_devices;
static enum cpuhp_state haltpoll_hp_state;

static __cpuidle int default_enter_idle(struct cpuidle_device *dev,
                                        struct cpuidle_driver *drv, int index)
{
        if (current_clr_polling_and_test())
                return index;

        arch_cpu_idle();
        return index;
}

static struct cpuidle_driver haltpoll_driver = {
        .name = "haltpoll",
        .governor = "haltpoll",
        .states = {
                { /* entry 0 is for polling */ },
                {
                        .enter                  = default_enter_idle,
                        .exit_latency           = 1,
                        .target_residency       = 1,
                        .power_usage            = -1,
                        .name                   = "haltpoll idle",
                        .desc                   = "default architecture idle",
                },
        },
        .safe_state_index = 0,
        .state_count = 2,
};

static int haltpoll_cpu_online(unsigned int cpu)
{
        struct cpuidle_device *dev;

        dev = per_cpu_ptr(haltpoll_cpuidle_devices, cpu);
        if (!dev->registered) {
                dev->cpu = cpu;
                if (cpuidle_register_device(dev)) {
                        pr_notice("cpuidle_register_device %d failed!\n", cpu);
                        return -EIO;
                }
                arch_haltpoll_enable(cpu);
        }

        return 0;
}

static int haltpoll_cpu_offline(unsigned int cpu)
{
        struct cpuidle_device *dev;

        dev = per_cpu_ptr(haltpoll_cpuidle_devices, cpu);
        if (dev->registered) {
                arch_haltpoll_disable(cpu);
                cpuidle_unregister_device(dev);
        }

        return 0;
}

static void haltpoll_uninit(void)
{
        if (haltpoll_hp_state)
                cpuhp_remove_state(haltpoll_hp_state);
        cpuidle_unregister_driver(&haltpoll_driver);

        free_percpu(haltpoll_cpuidle_devices);
        haltpoll_cpuidle_devices = NULL;
}

static bool haltpoll_want(void)
{
        return kvm_para_has_hint(KVM_HINTS_REALTIME) || force;
}

static int __init haltpoll_init(void)
{
        int ret;
        struct cpuidle_driver *drv = &haltpoll_driver;

        /* Do not load haltpoll if idle= is passed */
        if (boot_option_idle_override != IDLE_NO_OVERRIDE)
                return -ENODEV;

        if (!kvm_para_available() || !haltpoll_want())
                return -ENODEV;

        cpuidle_poll_state_init(drv);

        ret = cpuidle_register_driver(drv);
        if (ret < 0)
                return ret;

        haltpoll_cpuidle_devices = alloc_percpu(struct cpuidle_device);
        if (haltpoll_cpuidle_devices == NULL) {
                cpuidle_unregister_driver(drv);
                return -ENOMEM;
        }

        ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "cpuidle/haltpoll:online",
                                haltpoll_cpu_online, haltpoll_cpu_offline);
        if (ret < 0) {
                haltpoll_uninit();
        } else {
                haltpoll_hp_state = ret;
                ret = 0;
        }

        return ret;
}

static void __exit haltpoll_exit(void)
{
        haltpoll_uninit();
}

module_init(haltpoll_init);
module_exit(haltpoll_exit);
MODULE_DESCRIPTION("cpuidle driver for haltpoll governor");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Marcelo Tosatti <mtosatti@redhat.com>");