1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * (C) 2003 - 2004 Dominik Brodowski <linux@dominikbrodowski.de>
4 *
5 * Based on code found in
6 * linux/arch/i386/kernel/cpu/cpufreq/speedstep-centrino.c
7 * and originally developed by Jeremy Fitzhardinge.
8 *
9 * USAGE: simply run it to decode the current settings on CPU 0,
10 * or pass the CPU number as argument, or pass the MSR content
11 * as argument.
12 */
13
14#include <stdio.h>
15#include <stdlib.h>
16#include <stdint.h>
17#include <unistd.h>
18#include <errno.h>
19#include <fcntl.h>
20
21#include <sys/types.h>
22#include <sys/stat.h>
23
24#define MCPU 32
25
26#define MSR_IA32_PERF_STATUS 0x198
27
28static int rdmsr(unsigned int cpu, unsigned int msr,
29 unsigned int *lo, unsigned int *hi)
30{
31 int fd;
32 char file[20];
33 unsigned long long val;
34 int retval = -1;
35
36 *lo = *hi = 0;
37
38 if (cpu > MCPU)
39 goto err1;
40
41 sprintf(file, "/dev/cpu/%d/msr", cpu);
42 fd = open(file, O_RDONLY);
43
44 if (fd < 0)
45 goto err1;
46
47 if (lseek(fd, msr, SEEK_CUR) == -1)
48 goto err2;
49
50 if (read(fd, &val, 8) != 8)
51 goto err2;
52
53 *lo = (uint32_t )(val & 0xffffffffull);
54 *hi = (uint32_t )(val>>32 & 0xffffffffull);
55
56 retval = 0;
57err2:
58 close(fd);
59err1:
60 return retval;
61}
62
63static void decode (unsigned int msr)
64{
65 unsigned int multiplier;
66 unsigned int mv;
67
68 multiplier = ((msr >> 8) & 0xFF);
69
70 mv = (((msr & 0xFF) * 16) + 700);
71
72 printf("0x%x means multiplier %d @ %d mV\n", msr, multiplier, mv);
73}
74
75static int decode_live(unsigned int cpu)
76{
77 unsigned int lo, hi;
78 int err;
79
80 err = rdmsr(cpu, MSR_IA32_PERF_STATUS, lo: &lo, hi: &hi);
81
82 if (err) {
83 printf("can't get MSR_IA32_PERF_STATUS for cpu %d\n", cpu);
84 printf("Possible trouble: you don't run an Enhanced SpeedStep capable cpu\n");
85 printf("or you are not root, or the msr driver is not present\n");
86 return 1;
87 }
88
89 decode(msr: lo);
90
91 return 0;
92}
93
94int main (int argc, char **argv)
95{
96 unsigned int cpu, mode = 0;
97
98 if (argc < 2)
99 cpu = 0;
100 else {
101 cpu = strtoul(argv[1], NULL, 0);
102 if (cpu >= MCPU)
103 mode = 1;
104 }
105
106 if (mode)
107 decode(msr: cpu);
108 else
109 decode_live(cpu);
110
111 return 0;
112}
113

source code of linux/tools/power/cpupower/debug/i386/centrino-decode.c