// SPDX-License-Identifier: GPL-2.0-only
/*
 *  Based on documentation provided by Dave Jones. Thanks!
 *
 *  BIG FAT DISCLAIMER: Work in progress code. Possibly *dangerous*
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/cpufreq.h>
#include <linux/ioport.h>
#include <linux/slab.h>
#include <linux/timex.h>
#include <linux/io.h>
#include <linux/delay.h>

#include <asm/cpu_device_id.h>
#include <asm/msr.h>
#include <asm/tsc.h>

#if IS_ENABLED(CONFIG_ACPI_PROCESSOR)
#include <linux/acpi.h>
#include <acpi/processor.h>
#endif

#define EPS_BRAND_C7M   0
#define EPS_BRAND_C7    1
#define EPS_BRAND_EDEN  2
#define EPS_BRAND_C3    3
#define EPS_BRAND_C7D   4

struct eps_cpu_data {
        u32 fsb;
#if IS_ENABLED(CONFIG_ACPI_PROCESSOR)
        u32 bios_limit;
#endif
        struct cpufreq_frequency_table freq_table[];
};

static struct eps_cpu_data *eps_cpu[NR_CPUS];

/* Module parameters */
static int freq_failsafe_off;
static int voltage_failsafe_off;
static int set_max_voltage;

#if IS_ENABLED(CONFIG_ACPI_PROCESSOR)
static int ignore_acpi_limit;

static struct acpi_processor_performance *eps_acpi_cpu_perf;

/* Minimum necessary to get acpi_processor_get_bios_limit() working */
static int eps_acpi_init(void)
{
        eps_acpi_cpu_perf = kzalloc_obj(*eps_acpi_cpu_perf);
        if (!eps_acpi_cpu_perf)
                return -ENOMEM;

        if (!zalloc_cpumask_var(&eps_acpi_cpu_perf->shared_cpu_map,
                                                                GFP_KERNEL)) {
                kfree(eps_acpi_cpu_perf);
                eps_acpi_cpu_perf = NULL;
                return -ENOMEM;
        }

        if (acpi_processor_register_performance(eps_acpi_cpu_perf, 0)) {
                free_cpumask_var(eps_acpi_cpu_perf->shared_cpu_map);
                kfree(eps_acpi_cpu_perf);
                eps_acpi_cpu_perf = NULL;
                return -EIO;
        }
        return 0;
}

static int eps_acpi_exit(struct cpufreq_policy *policy)
{
        if (eps_acpi_cpu_perf) {
                acpi_processor_unregister_performance(0);
                free_cpumask_var(eps_acpi_cpu_perf->shared_cpu_map);
                kfree(eps_acpi_cpu_perf);
                eps_acpi_cpu_perf = NULL;
        }
        return 0;
}
#endif

static unsigned int eps_get(unsigned int cpu)
{
        struct eps_cpu_data *centaur;
        u32 lo, hi;

        if (cpu)
                return 0;
        centaur = eps_cpu[cpu];
        if (centaur == NULL)
                return 0;

        /* Return current frequency */
        rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
        return centaur->fsb * ((lo >> 8) & 0xff);
}

static int eps_set_state(struct eps_cpu_data *centaur,
                         struct cpufreq_policy *policy,
                         u32 dest_state)
{
        u32 lo, hi;
        int i;

        /* Wait while CPU is busy */
        rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
        i = 0;
        while (lo & ((1 << 16) | (1 << 17))) {
                udelay(16);
                rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
                i++;
                if (unlikely(i > 64)) {
                        return -ENODEV;
                }
        }
        /* Set new multiplier and voltage */
        wrmsr(MSR_IA32_PERF_CTL, dest_state & 0xffff, 0);
        /* Wait until transition end */
        i = 0;
        do {
                udelay(16);
                rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
                i++;
                if (unlikely(i > 64)) {
                        return -ENODEV;
                }
        } while (lo & ((1 << 16) | (1 << 17)));

#ifdef DEBUG
        {
        u8 current_multiplier, current_voltage;

        /* Print voltage and multiplier */
        rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
        current_voltage = lo & 0xff;
        pr_info("Current voltage = %dmV\n", current_voltage * 16 + 700);
        current_multiplier = (lo >> 8) & 0xff;
        pr_info("Current multiplier = %d\n", current_multiplier);
        }
#endif
        return 0;
}

static int eps_target(struct cpufreq_policy *policy, unsigned int index)
{
        struct eps_cpu_data *centaur;
        unsigned int cpu = policy->cpu;
        unsigned int dest_state;
        int ret;

        if (unlikely(eps_cpu[cpu] == NULL))
                return -ENODEV;
        centaur = eps_cpu[cpu];

        /* Make frequency transition */
        dest_state = centaur->freq_table[index].driver_data & 0xffff;
        ret = eps_set_state(centaur, policy, dest_state);
        if (ret)
                pr_err("Timeout!\n");
        return ret;
}

static int eps_cpu_init(struct cpufreq_policy *policy)
{
        unsigned int i;
        u32 lo, hi;
        u64 val;
        u8 current_multiplier, current_voltage;
        u8 max_multiplier, max_voltage;
        u8 min_multiplier, min_voltage;
        u8 brand = 0;
        u32 fsb;
        struct eps_cpu_data *centaur;
        struct cpuinfo_x86 *c = &cpu_data(0);
        struct cpufreq_frequency_table *f_table;
        int k, step, voltage;
        int states;
#if IS_ENABLED(CONFIG_ACPI_PROCESSOR)
        unsigned int limit;
#endif

        if (policy->cpu != 0)
                return -ENODEV;

        /* Check brand */
        pr_info("Detected VIA ");

        switch (c->x86_model) {
        case 10:
                rdmsr(0x1153, lo, hi);
                brand = (((lo >> 2) ^ lo) >> 18) & 3;
                pr_cont("Model A ");
                break;
        case 13:
                rdmsr(0x1154, lo, hi);
                brand = (((lo >> 4) ^ (lo >> 2))) & 0x000000ff;
                pr_cont("Model D ");
                break;
        }

        switch (brand) {
        case EPS_BRAND_C7M:
                pr_cont("C7-M\n");
                break;
        case EPS_BRAND_C7:
                pr_cont("C7\n");
                break;
        case EPS_BRAND_EDEN:
                pr_cont("Eden\n");
                break;
        case EPS_BRAND_C7D:
                pr_cont("C7-D\n");
                break;
        case EPS_BRAND_C3:
                pr_cont("C3\n");
                return -ENODEV;
        }
        /* Enable Enhanced PowerSaver */
        rdmsrq(MSR_IA32_MISC_ENABLE, val);
        if (!(val & MSR_IA32_MISC_ENABLE_ENHANCED_SPEEDSTEP)) {
                val |= MSR_IA32_MISC_ENABLE_ENHANCED_SPEEDSTEP;
                wrmsrq(MSR_IA32_MISC_ENABLE, val);
                /* Can be locked at 0 */
                rdmsrq(MSR_IA32_MISC_ENABLE, val);
                if (!(val & MSR_IA32_MISC_ENABLE_ENHANCED_SPEEDSTEP)) {
                        pr_info("Can't enable Enhanced PowerSaver\n");
                        return -ENODEV;
                }
        }

        /* Print voltage and multiplier */
        rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
        current_voltage = lo & 0xff;
        pr_info("Current voltage = %dmV\n", current_voltage * 16 + 700);
        current_multiplier = (lo >> 8) & 0xff;
        pr_info("Current multiplier = %d\n", current_multiplier);

        /* Print limits */
        max_voltage = hi & 0xff;
        pr_info("Highest voltage = %dmV\n", max_voltage * 16 + 700);
        max_multiplier = (hi >> 8) & 0xff;
        pr_info("Highest multiplier = %d\n", max_multiplier);
        min_voltage = (hi >> 16) & 0xff;
        pr_info("Lowest voltage = %dmV\n", min_voltage * 16 + 700);
        min_multiplier = (hi >> 24) & 0xff;
        pr_info("Lowest multiplier = %d\n", min_multiplier);

        /* Sanity checks */
        if (current_multiplier == 0 || max_multiplier == 0
            || min_multiplier == 0)
                return -EINVAL;
        if (current_multiplier > max_multiplier
            || max_multiplier <= min_multiplier)
                return -EINVAL;
        if (current_voltage > 0x1f || max_voltage > 0x1f)
                return -EINVAL;
        if (max_voltage < min_voltage
            || current_voltage < min_voltage
            || current_voltage > max_voltage)
                return -EINVAL;

        /* Check for systems using underclocked CPU */
        if (!freq_failsafe_off && max_multiplier != current_multiplier) {
                pr_info("Your processor is running at different frequency then its maximum. Aborting.\n");
                pr_info("You can use freq_failsafe_off option to disable this check.\n");
                return -EINVAL;
        }
        if (!voltage_failsafe_off && max_voltage != current_voltage) {
                pr_info("Your processor is running at different voltage then its maximum. Aborting.\n");
                pr_info("You can use voltage_failsafe_off option to disable this check.\n");
                return -EINVAL;
        }

        /* Calc FSB speed */
        fsb = cpu_khz / current_multiplier;

#if IS_ENABLED(CONFIG_ACPI_PROCESSOR)
        /* Check for ACPI processor speed limit */
        if (!ignore_acpi_limit && !eps_acpi_init()) {
                if (!acpi_processor_get_bios_limit(policy->cpu, &limit)) {
                        pr_info("ACPI limit %u.%uGHz\n",
                                limit/1000000,
                                (limit%1000000)/10000);
                        eps_acpi_exit(policy);
                        /* Check if max_multiplier is in BIOS limits */
                        if (limit && max_multiplier * fsb > limit) {
                                pr_info("Aborting\n");
                                return -EINVAL;
                        }
                }
        }
#endif

        /* Allow user to set lower maximum voltage then that reported
         * by processor */
        if (brand == EPS_BRAND_C7M && set_max_voltage) {
                u32 v;

                /* Change mV to something hardware can use */
                v = (set_max_voltage - 700) / 16;
                /* Check if voltage is within limits */
                if (v >= min_voltage && v <= max_voltage) {
                        pr_info("Setting %dmV as maximum\n", v * 16 + 700);
                        max_voltage = v;
                }
        }

        /* Calc number of p-states supported */
        if (brand == EPS_BRAND_C7M)
                states = max_multiplier - min_multiplier + 1;
        else
                states = 2;

        /* Allocate private data and frequency table for current cpu */
        centaur = kzalloc_flex(*centaur, freq_table, states + 1);
        if (!centaur)
                return -ENOMEM;
        eps_cpu[0] = centaur;

        /* Copy basic values */
        centaur->fsb = fsb;
#if IS_ENABLED(CONFIG_ACPI_PROCESSOR)
        centaur->bios_limit = limit;
#endif

        /* Fill frequency and MSR value table */
        f_table = &centaur->freq_table[0];
        if (brand != EPS_BRAND_C7M) {
                f_table[0].frequency = fsb * min_multiplier;
                f_table[0].driver_data = (min_multiplier << 8) | min_voltage;
                f_table[1].frequency = fsb * max_multiplier;
                f_table[1].driver_data = (max_multiplier << 8) | max_voltage;
                f_table[2].frequency = CPUFREQ_TABLE_END;
        } else {
                k = 0;
                step = ((max_voltage - min_voltage) * 256)
                        / (max_multiplier - min_multiplier);
                for (i = min_multiplier; i <= max_multiplier; i++) {
                        voltage = (k * step) / 256 + min_voltage;
                        f_table[k].frequency = fsb * i;
                        f_table[k].driver_data = (i << 8) | voltage;
                        k++;
                }
                f_table[k].frequency = CPUFREQ_TABLE_END;
        }

        policy->cpuinfo.transition_latency = 140000; /* 844mV -> 700mV in ns */
        policy->freq_table = &centaur->freq_table[0];

        return 0;
}

static void eps_cpu_exit(struct cpufreq_policy *policy)
{
        unsigned int cpu = policy->cpu;

        /* Bye */
        kfree(eps_cpu[cpu]);
        eps_cpu[cpu] = NULL;
}

static struct cpufreq_driver eps_driver = {
        .verify         = cpufreq_generic_frequency_table_verify,
        .target_index   = eps_target,
        .init           = eps_cpu_init,
        .exit           = eps_cpu_exit,
        .get            = eps_get,
        .name           = "e_powersaver",
};


/* This driver will work only on Centaur C7 processors with
 * Enhanced SpeedStep/PowerSaver registers */
static const struct x86_cpu_id eps_cpu_id[] = {
        X86_MATCH_VENDOR_FAM_FEATURE(CENTAUR, 6, X86_FEATURE_EST, NULL),
        {}
};
MODULE_DEVICE_TABLE(x86cpu, eps_cpu_id);

static int __init eps_init(void)
{
        if (!x86_match_cpu(eps_cpu_id) || boot_cpu_data.x86_model < 10)
                return -ENODEV;
        if (cpufreq_register_driver(&eps_driver))
                return -EINVAL;
        return 0;
}

static void __exit eps_exit(void)
{
        cpufreq_unregister_driver(&eps_driver);
}

/* Allow user to overclock his machine or to change frequency to higher after
 * unloading module */
module_param(freq_failsafe_off, int, 0644);
MODULE_PARM_DESC(freq_failsafe_off, "Disable current vs max frequency check");
module_param(voltage_failsafe_off, int, 0644);
MODULE_PARM_DESC(voltage_failsafe_off, "Disable current vs max voltage check");
#if IS_ENABLED(CONFIG_ACPI_PROCESSOR)
module_param(ignore_acpi_limit, int, 0644);
MODULE_PARM_DESC(ignore_acpi_limit, "Don't check ACPI's processor speed limit");
#endif
module_param(set_max_voltage, int, 0644);
MODULE_PARM_DESC(set_max_voltage, "Set maximum CPU voltage (mV) C7-M only");

MODULE_AUTHOR("Rafal Bilski <rafalbilski@interia.pl>");
MODULE_DESCRIPTION("Enhanced PowerSaver driver for VIA C7 CPU's.");
MODULE_LICENSE("GPL");

module_init(eps_init);
module_exit(eps_exit);