// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *      elanfreq:       cpufreq driver for the AMD ELAN family
 *
 *      (c) Copyright 2002 Robert Schwebel <r.schwebel@pengutronix.de>
 *
 *      Parts of this code are (c) Sven Geggus <sven@geggus.net>
 *
 *      All Rights Reserved.
 *
 *      2002-02-13: - initial revision for 2.4.18-pre9 by Robert Schwebel
 */

#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 <asm/cpu_device_id.h>
#include <linux/timex.h>
#include <linux/io.h>

#define REG_CSCIR 0x22          /* Chip Setup and Control Index Register    */
#define REG_CSCDR 0x23          /* Chip Setup and Control Data  Register    */

/* Module parameter */
static int max_freq;

struct s_elan_multiplier {
        int clock;              /* frequency in kHz                         */
        int val40h;             /* PMU Force Mode register                  */
        int val80h;             /* CPU Clock Speed Register                 */
};

/*
 * It is important that the frequencies
 * are listed in ascending order here!
 */
static struct s_elan_multiplier elan_multiplier[] = {
        {1000,  0x02,   0x18},
        {2000,  0x02,   0x10},
        {4000,  0x02,   0x08},
        {8000,  0x00,   0x00},
        {16000, 0x00,   0x02},
        {33000, 0x00,   0x04},
        {66000, 0x01,   0x04},
        {99000, 0x01,   0x05}
};

static struct cpufreq_frequency_table elanfreq_table[] = {
        {0, 0,  1000},
        {0, 1,  2000},
        {0, 2,  4000},
        {0, 3,  8000},
        {0, 4,  16000},
        {0, 5,  33000},
        {0, 6,  66000},
        {0, 7,  99000},
        {0, 0,  CPUFREQ_TABLE_END},
};


/**
 *      elanfreq_get_cpu_frequency: determine current cpu speed
 *
 *      Finds out at which frequency the CPU of the Elan SOC runs
 *      at the moment. Frequencies from 1 to 33 MHz are generated
 *      the normal way, 66 and 99 MHz are called "Hyperspeed Mode"
 *      and have the rest of the chip running with 33 MHz.
 */

static unsigned int elanfreq_get_cpu_frequency(unsigned int cpu)
{
        u8 clockspeed_reg;    /* Clock Speed Register */

        local_irq_disable();
        outb_p(0x80, REG_CSCIR);
        clockspeed_reg = inb_p(REG_CSCDR);
        local_irq_enable();

        if ((clockspeed_reg & 0xE0) == 0xE0)
                return 0;

        /* Are we in CPU clock multiplied mode (66/99 MHz)? */
        if ((clockspeed_reg & 0xE0) == 0xC0) {
                if ((clockspeed_reg & 0x01) == 0)
                        return 66000;
                else
                        return 99000;
        }

        /* 33 MHz is not 32 MHz... */
        if ((clockspeed_reg & 0xE0) == 0xA0)
                return 33000;

        return (1<<((clockspeed_reg & 0xE0) >> 5)) * 1000;
}


static int elanfreq_target(struct cpufreq_policy *policy,
                            unsigned int state)
{
        /*
         * Access to the Elan's internal registers is indexed via
         * 0x22: Chip Setup & Control Register Index Register (CSCI)
         * 0x23: Chip Setup & Control Register Data  Register (CSCD)
         *
         */

        /*
         * 0x40 is the Power Management Unit's Force Mode Register.
         * Bit 6 enables Hyperspeed Mode (66/100 MHz core frequency)
         */

        local_irq_disable();
        outb_p(0x40, REG_CSCIR);                /* Disable hyperspeed mode */
        outb_p(0x00, REG_CSCDR);
        local_irq_enable();             /* wait till internal pipelines and */
        udelay(1000);                   /* buffers have cleaned up          */

        local_irq_disable();

        /* now, set the CPU clock speed register (0x80) */
        outb_p(0x80, REG_CSCIR);
        outb_p(elan_multiplier[state].val80h, REG_CSCDR);

        /* now, the hyperspeed bit in PMU Force Mode Register (0x40) */
        outb_p(0x40, REG_CSCIR);
        outb_p(elan_multiplier[state].val40h, REG_CSCDR);
        udelay(10000);
        local_irq_enable();

        return 0;
}
/*
 *      Module init and exit code
 */

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

        /* capability check */
        if ((c->x86_vendor != X86_VENDOR_AMD) ||
            (c->x86 != 4) || (c->x86_model != 10))
                return -ENODEV;

        /* max freq */
        if (!max_freq)
                max_freq = elanfreq_get_cpu_frequency(0);

        /* table init */
        cpufreq_for_each_entry(pos, elanfreq_table)
                if (pos->frequency > max_freq)
                        pos->frequency = CPUFREQ_ENTRY_INVALID;

        policy->freq_table = elanfreq_table;
        return 0;
}


#ifndef MODULE
/**
 * elanfreq_setup - elanfreq command line parameter parsing
 *
 * elanfreq command line parameter.  Use:
 *  elanfreq=66000
 * to set the maximum CPU frequency to 66 MHz. Note that in
 * case you do not give this boot parameter, the maximum
 * frequency will fall back to _current_ CPU frequency which
 * might be lower. If you build this as a module, use the
 * max_freq module parameter instead.
 */
static int __init elanfreq_setup(char *str)
{
        max_freq = simple_strtoul(str, &str, 0);
        pr_warn("You're using the deprecated elanfreq command line option. Use elanfreq.max_freq instead, please!\n");
        return 1;
}
__setup("elanfreq=", elanfreq_setup);
#endif


static struct cpufreq_driver elanfreq_driver = {
        .get            = elanfreq_get_cpu_frequency,
        .flags          = CPUFREQ_NO_AUTO_DYNAMIC_SWITCHING,
        .verify         = cpufreq_generic_frequency_table_verify,
        .target_index   = elanfreq_target,
        .init           = elanfreq_cpu_init,
        .name           = "elanfreq",
};

static const struct x86_cpu_id elan_id[] = {
        X86_MATCH_VENDOR_FAM_MODEL(AMD, 4, 10, NULL),
        {}
};
MODULE_DEVICE_TABLE(x86cpu, elan_id);

static int __init elanfreq_init(void)
{
        if (!x86_match_cpu(elan_id))
                return -ENODEV;
        return cpufreq_register_driver(&elanfreq_driver);
}


static void __exit elanfreq_exit(void)
{
        cpufreq_unregister_driver(&elanfreq_driver);
}


module_param(max_freq, int, 0444);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Robert Schwebel <r.schwebel@pengutronix.de>, "
                "Sven Geggus <sven@geggus.net>");
MODULE_DESCRIPTION("cpufreq driver for AMD's Elan CPUs");

module_init(elanfreq_init);
module_exit(elanfreq_exit);