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 
rdmsr(unsigned int cpu,unsigned int msr,unsigned int * lo,unsigned int * hi)28 static 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;
57 err2:
58 	close(fd);
59 err1:
60 	return retval;
61 }
62 
decode(unsigned int msr)63 static 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 
decode_live(unsigned int cpu)75 static 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, &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(lo);
90 
91 	return 0;
92 }
93 
main(int argc,char ** argv)94 int 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(cpu);
108 	else
109 		decode_live(cpu);
110 
111 	return 0;
112 }
113