/*
 * acpi_pad.c ACPI Processor Aggregator Driver
 *
 * Copyright (c) 2009, Intel Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
 *
 */

#include <linux/kernel.h>
#include <linux/cpumask.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/types.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/cpu.h>
#include <linux/clockchips.h>
#include <linux/slab.h>
#include <linux/acpi.h>
#include <asm/mwait.h>

#define ACPI_PROCESSOR_AGGREGATOR_CLASS "acpi_pad"
#define ACPI_PROCESSOR_AGGREGATOR_DEVICE_NAME "Processor Aggregator"
#define ACPI_PROCESSOR_AGGREGATOR_NOTIFY 0x80
static DEFINE_MUTEX(isolated_cpus_lock);
static DEFINE_MUTEX(round_robin_lock);

static unsigned long power_saving_mwait_eax;

static unsigned char tsc_detected_unstable;
static unsigned char tsc_marked_unstable;
static unsigned char lapic_detected_unstable;
static unsigned char lapic_marked_unstable;

static void power_saving_mwait_init(void)
{
        unsigned int eax, ebx, ecx, edx;
        unsigned int highest_cstate = 0;
        unsigned int highest_subcstate = 0;
        int i;

        if (!boot_cpu_has(X86_FEATURE_MWAIT))
                return;
        if (boot_cpu_data.cpuid_level < CPUID_MWAIT_LEAF)
                return;

        cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);

        if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED) ||
            !(ecx & CPUID5_ECX_INTERRUPT_BREAK))
                return;

        edx >>= MWAIT_SUBSTATE_SIZE;
        for (i = 0; i < 7 && edx; i++, edx >>= MWAIT_SUBSTATE_SIZE) {
                if (edx & MWAIT_SUBSTATE_MASK) {
                        highest_cstate = i;
                        highest_subcstate = edx & MWAIT_SUBSTATE_MASK;
                }
        }
        power_saving_mwait_eax = (highest_cstate << MWAIT_SUBSTATE_SIZE) |
                (highest_subcstate - 1);

#if defined(CONFIG_X86)
        switch (boot_cpu_data.x86_vendor) {
        case X86_VENDOR_AMD:
        case X86_VENDOR_INTEL:
                /*
                 * AMD Fam10h TSC will tick in all
                 * C/P/S0/S1 states when this bit is set.
                 */
                if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC))
                        tsc_detected_unstable = 1;
                if (!boot_cpu_has(X86_FEATURE_ARAT))
                        lapic_detected_unstable = 1;
                break;
        default:
                /* TSC & LAPIC could halt in idle */
                tsc_detected_unstable = 1;
                lapic_detected_unstable = 1;
        }
#endif
}

static unsigned long cpu_weight[NR_CPUS];
static int tsk_in_cpu[NR_CPUS] = {[0 ... NR_CPUS-1] = -1};
static DECLARE_BITMAP(pad_busy_cpus_bits, NR_CPUS);
static void round_robin_cpu(unsigned int tsk_index)
{
        struct cpumask *pad_busy_cpus = to_cpumask(pad_busy_cpus_bits);
        cpumask_var_t tmp;
        int cpu;
        unsigned long min_weight = -1;
        unsigned long uninitialized_var(preferred_cpu);

        if (!alloc_cpumask_var(&tmp, GFP_KERNEL))
                return;

        mutex_lock(&round_robin_lock);
        cpumask_clear(tmp);
        for_each_cpu(cpu, pad_busy_cpus)
                cpumask_or(tmp, tmp, topology_thread_cpumask(cpu));
        cpumask_andnot(tmp, cpu_online_mask, tmp);
        /* avoid HT sibilings if possible */
        if (cpumask_empty(tmp))
                cpumask_andnot(tmp, cpu_online_mask, pad_busy_cpus);
        if (cpumask_empty(tmp)) {
                mutex_unlock(&round_robin_lock);
                return;
        }
        for_each_cpu(cpu, tmp) {
                if (cpu_weight[cpu] < min_weight) {
                        min_weight = cpu_weight[cpu];
                        preferred_cpu = cpu;
                }
        }

        if (tsk_in_cpu[tsk_index] != -1)
                cpumask_clear_cpu(tsk_in_cpu[tsk_index], pad_busy_cpus);
        tsk_in_cpu[tsk_index] = preferred_cpu;
        cpumask_set_cpu(preferred_cpu, pad_busy_cpus);
        cpu_weight[preferred_cpu]++;
        mutex_unlock(&round_robin_lock);

        set_cpus_allowed_ptr(current, cpumask_of(preferred_cpu));
}

static void exit_round_robin(unsigned int tsk_index)
{
        struct cpumask *pad_busy_cpus = to_cpumask(pad_busy_cpus_bits);
        cpumask_clear_cpu(tsk_in_cpu[tsk_index], pad_busy_cpus);
        tsk_in_cpu[tsk_index] = -1;
}

static unsigned int idle_pct = 5; /* percentage */
static unsigned int round_robin_time = 1; /* second */
static int power_saving_thread(void *data)
{
        struct sched_param param = {.sched_priority = 1};
        int do_sleep;
        unsigned int tsk_index = (unsigned long)data;
        u64 last_jiffies = 0;

        sched_setscheduler(current, SCHED_RR, &param);

        while (!kthread_should_stop()) {
                int cpu;
                unsigned long expire_time;

                try_to_freeze();

                /* round robin to cpus */
                expire_time = last_jiffies + round_robin_time * HZ;
                if (time_before(expire_time, jiffies)) {
                        last_jiffies = jiffies;
                        round_robin_cpu(tsk_index);
                }

                do_sleep = 0;

                expire_time = jiffies + HZ * (100 - idle_pct) / 100;

                while (!need_resched()) {
                        if (tsc_detected_unstable && !tsc_marked_unstable) {
                                /* TSC could halt in idle, so notify users */
                                mark_tsc_unstable("TSC halts in idle");
                                tsc_marked_unstable = 1;
                        }
                        if (lapic_detected_unstable && !lapic_marked_unstable) {
                                int i;
                                /* LAPIC could halt in idle, so notify users */
                                for_each_online_cpu(i)
                                        clockevents_notify(
                                                CLOCK_EVT_NOTIFY_BROADCAST_ON,
                                                &i);
                                lapic_marked_unstable = 1;
                        }
                        local_irq_disable();
                        cpu = smp_processor_id();
                        if (lapic_marked_unstable)
                                clockevents_notify(
                                        CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
                        stop_critical_timings();

                        mwait_idle_with_hints(power_saving_mwait_eax, 1);

                        start_critical_timings();
                        if (lapic_marked_unstable)
                                clockevents_notify(
                                        CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
                        local_irq_enable();

                        if (time_before(expire_time, jiffies)) {
                                do_sleep = 1;
                                break;
                        }
                }

                /*
                 * current sched_rt has threshold for rt task running time.
                 * When a rt task uses 95% CPU time, the rt thread will be
                 * scheduled out for 5% CPU time to not starve other tasks. But
                 * the mechanism only works when all CPUs have RT task running,
                 * as if one CPU hasn't RT task, RT task from other CPUs will
                 * borrow CPU time from this CPU and cause RT task use > 95%
                 * CPU time. To make 'avoid starvation' work, takes a nap here.
                 */
                if (unlikely(do_sleep))
                        schedule_timeout_killable(HZ * idle_pct / 100);

                /* If an external event has set the need_resched flag, then
                 * we need to deal with it, or this loop will continue to
                 * spin without calling __mwait().
                 */
                if (unlikely(need_resched()))
                        schedule();
        }

        exit_round_robin(tsk_index);
        return 0;
}

static struct task_struct *ps_tsks[NR_CPUS];
static unsigned int ps_tsk_num;
static int create_power_saving_task(void)
{
        int rc;

        ps_tsks[ps_tsk_num] = kthread_run(power_saving_thread,
                (void *)(unsigned long)ps_tsk_num,
                "acpi_pad/%d", ps_tsk_num);

        if (IS_ERR(ps_tsks[ps_tsk_num])) {
                rc = PTR_ERR(ps_tsks[ps_tsk_num]);
                ps_tsks[ps_tsk_num] = NULL;
        } else {
                rc = 0;
                ps_tsk_num++;
        }

        return rc;
}

static void destroy_power_saving_task(void)
{
        if (ps_tsk_num > 0) {
                ps_tsk_num--;
                kthread_stop(ps_tsks[ps_tsk_num]);
                ps_tsks[ps_tsk_num] = NULL;
        }
}

static void set_power_saving_task_num(unsigned int num)
{
        if (num > ps_tsk_num) {
                while (ps_tsk_num < num) {
                        if (create_power_saving_task())
                                return;
                }
        } else if (num < ps_tsk_num) {
                while (ps_tsk_num > num)
                        destroy_power_saving_task();
        }
}

static void acpi_pad_idle_cpus(unsigned int num_cpus)
{
        get_online_cpus();

        num_cpus = min_t(unsigned int, num_cpus, num_online_cpus());
        set_power_saving_task_num(num_cpus);

        put_online_cpus();
}

static uint32_t acpi_pad_idle_cpus_num(void)
{
        return ps_tsk_num;
}

static ssize_t acpi_pad_rrtime_store(struct device *dev,
        struct device_attribute *attr, const char *buf, size_t count)
{
        unsigned long num;
        if (kstrtoul(buf, 0, &num))
                return -EINVAL;
        if (num < 1 || num >= 100)
                return -EINVAL;
        mutex_lock(&isolated_cpus_lock);
        round_robin_time = num;
        mutex_unlock(&isolated_cpus_lock);
        return count;
}

static ssize_t acpi_pad_rrtime_show(struct device *dev,
        struct device_attribute *attr, char *buf)
{
        return scnprintf(buf, PAGE_SIZE, "%d\n", round_robin_time);
}
static DEVICE_ATTR(rrtime, S_IRUGO|S_IWUSR,
        acpi_pad_rrtime_show,
        acpi_pad_rrtime_store);

static ssize_t acpi_pad_idlepct_store(struct device *dev,
        struct device_attribute *attr, const char *buf, size_t count)
{
        unsigned long num;
        if (kstrtoul(buf, 0, &num))
                return -EINVAL;
        if (num < 1 || num >= 100)
                return -EINVAL;
        mutex_lock(&isolated_cpus_lock);
        idle_pct = num;
        mutex_unlock(&isolated_cpus_lock);
        return count;
}

static ssize_t acpi_pad_idlepct_show(struct device *dev,
        struct device_attribute *attr, char *buf)
{
        return scnprintf(buf, PAGE_SIZE, "%d\n", idle_pct);
}
static DEVICE_ATTR(idlepct, S_IRUGO|S_IWUSR,
        acpi_pad_idlepct_show,
        acpi_pad_idlepct_store);

static ssize_t acpi_pad_idlecpus_store(struct device *dev,
        struct device_attribute *attr, const char *buf, size_t count)
{
        unsigned long num;
        if (kstrtoul(buf, 0, &num))
                return -EINVAL;
        mutex_lock(&isolated_cpus_lock);
        acpi_pad_idle_cpus(num);
        mutex_unlock(&isolated_cpus_lock);
        return count;
}

static ssize_t acpi_pad_idlecpus_show(struct device *dev,
        struct device_attribute *attr, char *buf)
{
        int n = 0;
        n = cpumask_scnprintf(buf, PAGE_SIZE-2, to_cpumask(pad_busy_cpus_bits));
        buf[n++] = '\n';
        buf[n] = '\0';
        return n;
}
static DEVICE_ATTR(idlecpus, S_IRUGO|S_IWUSR,
        acpi_pad_idlecpus_show,
        acpi_pad_idlecpus_store);

static int acpi_pad_add_sysfs(struct acpi_device *device)
{
        int result;

        result = device_create_file(&device->dev, &dev_attr_idlecpus);
        if (result)
                return -ENODEV;
        result = device_create_file(&device->dev, &dev_attr_idlepct);
        if (result) {
                device_remove_file(&device->dev, &dev_attr_idlecpus);
                return -ENODEV;
        }
        result = device_create_file(&device->dev, &dev_attr_rrtime);
        if (result) {
                device_remove_file(&device->dev, &dev_attr_idlecpus);
                device_remove_file(&device->dev, &dev_attr_idlepct);
                return -ENODEV;
        }
        return 0;
}

static void acpi_pad_remove_sysfs(struct acpi_device *device)
{
        device_remove_file(&device->dev, &dev_attr_idlecpus);
        device_remove_file(&device->dev, &dev_attr_idlepct);
        device_remove_file(&device->dev, &dev_attr_rrtime);
}

/*
 * Query firmware how many CPUs should be idle
 * return -1 on failure
 */
static int acpi_pad_pur(acpi_handle handle)
{
        struct acpi_buffer buffer = {ACPI_ALLOCATE_BUFFER, NULL};
        union acpi_object *package;
        int num = -1;

        if (ACPI_FAILURE(acpi_evaluate_object(handle, "_PUR", NULL, &buffer)))
                return num;

        if (!buffer.length || !buffer.pointer)
                return num;

        package = buffer.pointer;

        if (package->type == ACPI_TYPE_PACKAGE &&
                package->package.count == 2 &&
                package->package.elements[0].integer.value == 1) /* rev 1 */

                num = package->package.elements[1].integer.value;

        kfree(buffer.pointer);
        return num;
}

static void acpi_pad_handle_notify(acpi_handle handle)
{
        int num_cpus;
        uint32_t idle_cpus;
        struct acpi_buffer param = {
                .length = 4,
                .pointer = (void *)&idle_cpus,
        };

        mutex_lock(&isolated_cpus_lock);
        num_cpus = acpi_pad_pur(handle);
        if (num_cpus < 0) {
                mutex_unlock(&isolated_cpus_lock);
                return;
        }
        acpi_pad_idle_cpus(num_cpus);
        idle_cpus = acpi_pad_idle_cpus_num();
        acpi_evaluate_ost(handle, ACPI_PROCESSOR_AGGREGATOR_NOTIFY, 0, &param);
        mutex_unlock(&isolated_cpus_lock);
}

static void acpi_pad_notify(acpi_handle handle, u32 event,
        void *data)
{
        struct acpi_device *device = data;

        switch (event) {
        case ACPI_PROCESSOR_AGGREGATOR_NOTIFY:
                acpi_pad_handle_notify(handle);
                acpi_bus_generate_netlink_event(device->pnp.device_class,
                        dev_name(&device->dev), event, 0);
                break;
        default:
                pr_warn("Unsupported event [0x%x]\n", event);
                break;
        }
}

static int acpi_pad_add(struct acpi_device *device)
{
        acpi_status status;

        strcpy(acpi_device_name(device), ACPI_PROCESSOR_AGGREGATOR_DEVICE_NAME);
        strcpy(acpi_device_class(device), ACPI_PROCESSOR_AGGREGATOR_CLASS);

        if (acpi_pad_add_sysfs(device))
                return -ENODEV;

        status = acpi_install_notify_handler(device->handle,
                ACPI_DEVICE_NOTIFY, acpi_pad_notify, device);
        if (ACPI_FAILURE(status)) {
                acpi_pad_remove_sysfs(device);
                return -ENODEV;
        }

        return 0;
}

static int acpi_pad_remove(struct acpi_device *device)
{
        mutex_lock(&isolated_cpus_lock);
        acpi_pad_idle_cpus(0);
        mutex_unlock(&isolated_cpus_lock);

        acpi_remove_notify_handler(device->handle,
                ACPI_DEVICE_NOTIFY, acpi_pad_notify);
        acpi_pad_remove_sysfs(device);
        return 0;
}

static const struct acpi_device_id pad_device_ids[] = {
        {"ACPI000C", 0},
        {"", 0},
};
MODULE_DEVICE_TABLE(acpi, pad_device_ids);

static struct acpi_driver acpi_pad_driver = {
        .name = "processor_aggregator",
        .class = ACPI_PROCESSOR_AGGREGATOR_CLASS,
        .ids = pad_device_ids,
        .ops = {
                .add = acpi_pad_add,
                .remove = acpi_pad_remove,
        },
};

static int __init acpi_pad_init(void)
{
        power_saving_mwait_init();
        if (power_saving_mwait_eax == 0)
                return -EINVAL;

        return acpi_bus_register_driver(&acpi_pad_driver);
}

static void __exit acpi_pad_exit(void)
{
        acpi_bus_unregister_driver(&acpi_pad_driver);
}

module_init(acpi_pad_init);
module_exit(acpi_pad_exit);
MODULE_AUTHOR("Shaohua Li<shaohua.li@intel.com>");
MODULE_DESCRIPTION("ACPI Processor Aggregator Driver");
MODULE_LICENSE("GPL");