1// SPDX-License-Identifier: GPL-2.0
2#include <linux/types.h>
3#include <math.h>
4#include <string.h>
5#include <stdlib.h>
6
7#include "../../../util/debug.h"
8#include "../../../util/tsc.h"
9#include "cpuid.h"
10
11u64 rdtsc(void)
12{
13	unsigned int low, high;
14
15	asm volatile("rdtsc" : "=a" (low), "=d" (high));
16
17	return low | ((u64)high) << 32;
18}
19
20/*
21 * Derive the TSC frequency in Hz from the /proc/cpuinfo, for example:
22 * ...
23 * model name      : Intel(R) Xeon(R) Gold 6154 CPU @ 3.00GHz
24 * ...
25 * will return 3000000000.
26 */
27static double cpuinfo_tsc_freq(void)
28{
29	double result = 0;
30	FILE *cpuinfo;
31	char *line = NULL;
32	size_t len = 0;
33
34	cpuinfo = fopen("/proc/cpuinfo", "r");
35	if (!cpuinfo) {
36		pr_err("Failed to read /proc/cpuinfo for TSC frequency\n");
37		return NAN;
38	}
39	while (getline(&line, &len, cpuinfo) > 0) {
40		if (!strncmp(line, "model name", 10)) {
41			char *pos = strstr(line + 11, " @ ");
42
43			if (pos && sscanf(pos, " @ %lfGHz", &result) == 1) {
44				result *= 1000000000;
45				goto out;
46			}
47		}
48	}
49out:
50	if (fpclassify(result) == FP_ZERO)
51		pr_err("Failed to find TSC frequency in /proc/cpuinfo\n");
52
53	free(line);
54	fclose(cpuinfo);
55	return result;
56}
57
58double arch_get_tsc_freq(void)
59{
60	unsigned int a, b, c, d, lvl;
61	static bool cached;
62	static double tsc;
63	char vendor[16];
64
65	if (cached)
66		return tsc;
67
68	cached = true;
69	get_cpuid_0(vendor, &lvl);
70	if (!strstr(vendor, "Intel"))
71		return 0;
72
73	/*
74	 * Don't support Time Stamp Counter and
75	 * Nominal Core Crystal Clock Information Leaf.
76	 */
77	if (lvl < 0x15) {
78		tsc = cpuinfo_tsc_freq();
79		return tsc;
80	}
81
82	cpuid(0x15, 0, &a, &b, &c, &d);
83	/* TSC frequency is not enumerated */
84	if (!a || !b || !c) {
85		tsc = cpuinfo_tsc_freq();
86		return tsc;
87	}
88
89	tsc = (double)c * (double)b / (double)a;
90	return tsc;
91}
92