// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *      sc520_freq.c: cpufreq driver for the AMD Elan sc520
 *
 *      Copyright (C) 2005 Sean Young <sean@mess.org>
 *
 *      Based on elanfreq.c
 *
 *      2005-03-30: - initial revision
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>

#include <linux/delay.h>
#include <linux/cpufreq.h>
#include <linux/timex.h>
#include <linux/io.h>

#include <asm/cpu_device_id.h>

#define MMCR_BASE       0xfffef000      /* The default base address */
#define OFFS_CPUCTL     0x2   /* CPU Control Register */

static __u8 __iomem *cpuctl;

static struct cpufreq_frequency_table sc520_freq_table[] = {
        {0, 0x01,       100000},
        {0, 0x02,       133000},
        {0, 0,  CPUFREQ_TABLE_END},
};

static unsigned int sc520_freq_get_cpu_frequency(unsigned int cpu)
{
        u8 clockspeed_reg = *cpuctl;

        switch (clockspeed_reg & 0x03) {
        default:
                pr_err("error: cpuctl register has unexpected value %02x\n",
                       clockspeed_reg);
                fallthrough;
        case 0x01:
                return 100000;
        case 0x02:
                return 133000;
        }
}

static int sc520_freq_target(struct cpufreq_policy *policy, unsigned int state)
{

        u8 clockspeed_reg;

        local_irq_disable();

        clockspeed_reg = *cpuctl & ~0x03;
        *cpuctl = clockspeed_reg | sc520_freq_table[state].driver_data;

        local_irq_enable();

        return 0;
}

/*
 *      Module init and exit code
 */

static int sc520_freq_cpu_init(struct cpufreq_policy *policy)
{
        struct cpuinfo_x86 *c = &cpu_data(0);

        /* capability check */
        if (c->x86_vendor != X86_VENDOR_AMD ||
            c->x86 != 4 || c->x86_model != 9)
                return -ENODEV;

        /* cpuinfo and default policy values */
        policy->cpuinfo.transition_latency = 1000000; /* 1ms */
        policy->freq_table = sc520_freq_table;

        return 0;
}


static struct cpufreq_driver sc520_freq_driver = {
        .get    = sc520_freq_get_cpu_frequency,
        .verify = cpufreq_generic_frequency_table_verify,
        .target_index = sc520_freq_target,
        .init   = sc520_freq_cpu_init,
        .name   = "sc520_freq",
};

static const struct x86_cpu_id sc520_ids[] = {
        X86_MATCH_VENDOR_FAM_MODEL(AMD, 4, 9, NULL),
        {}
};
MODULE_DEVICE_TABLE(x86cpu, sc520_ids);

static int __init sc520_freq_init(void)
{
        int err;

        if (!x86_match_cpu(sc520_ids))
                return -ENODEV;

        cpuctl = ioremap((unsigned long)(MMCR_BASE + OFFS_CPUCTL), 1);
        if (!cpuctl) {
                pr_err("sc520_freq: error: failed to remap memory\n");
                return -ENOMEM;
        }

        err = cpufreq_register_driver(&sc520_freq_driver);
        if (err)
                iounmap(cpuctl);

        return err;
}


static void __exit sc520_freq_exit(void)
{
        cpufreq_unregister_driver(&sc520_freq_driver);
        iounmap(cpuctl);
}


MODULE_LICENSE("GPL");
MODULE_AUTHOR("Sean Young <sean@mess.org>");
MODULE_DESCRIPTION("cpufreq driver for AMD's Elan sc520 CPU");

module_init(sc520_freq_init);
module_exit(sc520_freq_exit);