// SPDX-License-Identifier: GPL-2.0-only
/*
 * acpi_pad.c ACPI Processor Aggregator Driver
 *
 * Copyright (c) 2009, Intel Corporation.
 */

#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 <uapi/linux/sched/types.h>
#include <linux/freezer.h>
#include <linux/cpu.h>
#include <linux/tick.h>
#include <linux/slab.h>
#include <linux/acpi.h>
#include <linux/perf_event.h>
#include <linux/platform_device.h>
#include <asm/cpuid/api.h>
#include <asm/mwait.h>
#include <xen/xen.h>

#define ACPI_PROCESSOR_AGGREGATOR_CLASS "acpi_pad"
#define ACPI_PROCESSOR_AGGREGATOR_DEVICE_NAME "Processor Aggregator"
#define ACPI_PROCESSOR_AGGREGATOR_NOTIFY 0x80

#define ACPI_PROCESSOR_AGGREGATOR_STATUS_SUCCESS        0
#define ACPI_PROCESSOR_AGGREGATOR_STATUS_NO_ACTION      1

static DEFINE_MUTEX(isolated_cpus_lock);
static DEFINE_MUTEX(round_robin_lock);

static unsigned int power_saving_mwait_eax;

static unsigned char tsc_detected_unstable;
static unsigned char tsc_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;

        cpuid(CPUID_LEAF_MWAIT, &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_HYGON:
        case X86_VENDOR_AMD:
        case X86_VENDOR_INTEL:
        case X86_VENDOR_ZHAOXIN:
        case X86_VENDOR_CENTAUR:
                /*
                 * 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;
                break;
        default:
                /* TSC could halt in idle */
                tsc_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 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_sibling_cpumask(cpu));
        cpumask_andnot(tmp, cpu_online_mask, tmp);
        /* avoid HT siblings if possible */
        if (cpumask_empty(tmp))
                cpumask_andnot(tmp, cpu_online_mask, pad_busy_cpus);
        if (cpumask_empty(tmp)) {
                mutex_unlock(&round_robin_lock);
                free_cpumask_var(tmp);
                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));

        free_cpumask_var(tmp);
}

static void exit_round_robin(unsigned int tsk_index)
{
        struct cpumask *pad_busy_cpus = to_cpumask(pad_busy_cpus_bits);

        if (tsk_in_cpu[tsk_index] != -1) {
                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)
{
        int do_sleep;
        unsigned int tsk_index = (unsigned long)data;
        u64 last_jiffies = 0;

        sched_set_fifo_low(current);

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

                /* 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;
                        }
                        local_irq_disable();

                        perf_lopwr_cb(true);

                        tick_broadcast_enable();
                        tick_broadcast_enter();
                        stop_critical_timings();

                        mwait_idle_with_hints(power_saving_mwait_eax, 1);

                        start_critical_timings();
                        tick_broadcast_exit();

                        perf_lopwr_cb(false);

                        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)
{
        cpus_read_lock();

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

        cpus_read_unlock();
}

static uint32_t acpi_pad_idle_cpus_num(void)
{
        return ps_tsk_num;
}

static ssize_t 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 rrtime_show(struct device *dev,
        struct device_attribute *attr, char *buf)
{
        return sysfs_emit(buf, "%d\n", round_robin_time);
}
static DEVICE_ATTR_RW(rrtime);

static ssize_t 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 idlepct_show(struct device *dev,
        struct device_attribute *attr, char *buf)
{
        return sysfs_emit(buf, "%d\n", idle_pct);
}
static DEVICE_ATTR_RW(idlepct);

static ssize_t 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 idlecpus_show(struct device *dev,
        struct device_attribute *attr, char *buf)
{
        return cpumap_print_to_pagebuf(false, buf,
                                       to_cpumask(pad_busy_cpus_bits));
}

static DEVICE_ATTR_RW(idlecpus);

static struct attribute *acpi_pad_attrs[] = {
        &dev_attr_idlecpus.attr,
        &dev_attr_idlepct.attr,
        &dev_attr_rrtime.attr,
        NULL
};

ATTRIBUTE_GROUPS(acpi_pad);

/*
 * 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,
        };
        u32 status;

        mutex_lock(&isolated_cpus_lock);
        num_cpus = acpi_pad_pur(handle);
        if (num_cpus < 0) {
                /* The ACPI specification says that if no action was performed when
                 * processing the _PUR object, _OST should still be evaluated, albeit
                 * with a different status code.
                 */
                status = ACPI_PROCESSOR_AGGREGATOR_STATUS_NO_ACTION;
        } else {
                status = ACPI_PROCESSOR_AGGREGATOR_STATUS_SUCCESS;
                acpi_pad_idle_cpus(num_cpus);
        }

        idle_cpus = acpi_pad_idle_cpus_num();
        acpi_evaluate_ost(handle, ACPI_PROCESSOR_AGGREGATOR_NOTIFY, status, &param);
        mutex_unlock(&isolated_cpus_lock);
}

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

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

static int acpi_pad_probe(struct platform_device *pdev)
{
        struct acpi_device *adev = ACPI_COMPANION(&pdev->dev);
        acpi_status status;

        strscpy(acpi_device_name(adev), ACPI_PROCESSOR_AGGREGATOR_DEVICE_NAME);
        strscpy(acpi_device_class(adev), ACPI_PROCESSOR_AGGREGATOR_CLASS);

        status = acpi_install_notify_handler(adev->handle,
                ACPI_DEVICE_NOTIFY, acpi_pad_notify, adev);

        if (ACPI_FAILURE(status))
                return -ENODEV;

        return 0;
}

static void acpi_pad_remove(struct platform_device *pdev)
{
        struct acpi_device *adev = ACPI_COMPANION(&pdev->dev);

        mutex_lock(&isolated_cpus_lock);
        acpi_pad_idle_cpus(0);
        mutex_unlock(&isolated_cpus_lock);

        acpi_remove_notify_handler(adev->handle,
                ACPI_DEVICE_NOTIFY, acpi_pad_notify);
}

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

static struct platform_driver acpi_pad_driver = {
        .probe = acpi_pad_probe,
        .remove = acpi_pad_remove,
        .driver = {
                .dev_groups = acpi_pad_groups,
                .name = "processor_aggregator",
                .acpi_match_table = pad_device_ids,
        },
};

static int __init acpi_pad_init(void)
{
        /* Xen ACPI PAD is used when running as Xen Dom0. */
        if (xen_initial_domain())
                return -ENODEV;

        power_saving_mwait_init();
        if (power_saving_mwait_eax == 0)
                return -EINVAL;

        return platform_driver_register(&acpi_pad_driver);
}

static void __exit acpi_pad_exit(void)
{
        platform_driver_unregister(&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");