// SPDX-License-Identifier: GPL-2.0-only
/*
 *  (C) 2003 - 2004  Dominik Brodowski <linux@dominikbrodowski.de>
 *
 * Based on code found in
 * linux/arch/i386/kernel/cpu/cpufreq/speedstep-centrino.c
 * and originally developed by Jeremy Fitzhardinge.
 *
 * USAGE: simply run it to decode the current settings on CPU 0,
 *        or pass the CPU number as argument, or pass the MSR content
 *        as argument.
 */

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>

#include <sys/types.h>
#include <sys/stat.h>

#define MCPU    32

#define MSR_IA32_PERF_STATUS    0x198

static int rdmsr(unsigned int cpu, unsigned int msr,
                 unsigned int *lo, unsigned int *hi)
{
        int fd;
        char file[20];
        unsigned long long val;
        int retval = -1;

        *lo = *hi = 0;

        if (cpu > MCPU)
                goto err1;

        sprintf(file, "/dev/cpu/%d/msr", cpu);
        fd = open(file, O_RDONLY);

        if (fd < 0)
                goto err1;

        if (lseek(fd, msr, SEEK_CUR) == -1)
                goto err2;

        if (read(fd, &val, 8) != 8)
                goto err2;

        *lo = (uint32_t )(val & 0xffffffffull);
        *hi = (uint32_t )(val>>32 & 0xffffffffull);

        retval = 0;
err2:
        close(fd);
err1:
        return retval;
}

static void decode (unsigned int msr)
{
        unsigned int multiplier;
        unsigned int mv;

        multiplier = ((msr >> 8) & 0xFF);

        mv = (((msr & 0xFF) * 16) + 700);

        printf("0x%x means multiplier %d @ %d mV\n", msr, multiplier, mv);
}

static int decode_live(unsigned int cpu)
{
        unsigned int lo, hi;
        int err;

        err = rdmsr(cpu, MSR_IA32_PERF_STATUS, &lo, &hi);

        if (err) {
                printf("can't get MSR_IA32_PERF_STATUS for cpu %d\n", cpu);
                printf("Possible trouble: you don't run an Enhanced SpeedStep capable cpu\n");
                printf("or you are not root, or the msr driver is not present\n");
                return 1;
        }

        decode(lo);

        return 0;
}

int main (int argc, char **argv)
{
        unsigned int cpu, mode = 0;

        if (argc < 2)
                cpu = 0;
        else {
                cpu = strtoul(argv[1], NULL, 0);
                if (cpu >= MCPU)
                        mode = 1;
        }

        if (mode)
                decode(cpu);
        else
                decode_live(cpu);

        return 0;
}