1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * test module to check whether the TSC-based delay routine continues
4 * to work properly after cpufreq transitions. Needs ACPI to work
5 * properly.
6 *
7 * Based partly on the Power Management Timer (PMTMR) code to be found
8 * in arch/i386/kernel/timers/timer_pm.c on recent 2.6. kernels, especially
9 * code written by John Stultz. The read_pmtmr function was copied verbatim
10 * from that file.
11 *
12 * (C) 2004 Dominik Brodowski
13 *
14 * To use:
15 * 1.) pass clock=tsc to the kernel on your bootloader
16 * 2.) modprobe this module (it'll fail)
17 * 3.) change CPU frequency
18 * 4.) modprobe this module again
19 * 5.) if the third value, "diff_pmtmr", changes between 2. and 4., the
20 *     TSC-based delay routine on the Linux kernel does not correctly
21 *     handle the cpufreq transition. Please report this to
22 *     linux-pm@vger.kernel.org
23 */
24
25#include <linux/kernel.h>
26#include <linux/module.h>
27#include <linux/init.h>
28#include <linux/delay.h>
29#include <linux/acpi.h>
30#include <asm/io.h>
31
32static int pm_tmr_ioport = 0;
33
34/*helper function to safely read acpi pm timesource*/
35static u32 read_pmtmr(void)
36{
37	u32 v1=0,v2=0,v3=0;
38	/* It has been reported that because of various broken
39	 * chipsets (ICH4, PIIX4 and PIIX4E) where the ACPI PM time
40	 * source is not latched, so you must read it multiple
41	 * times to insure a safe value is read.
42	 */
43	do {
44		v1 = inl(pm_tmr_ioport);
45		v2 = inl(pm_tmr_ioport);
46		v3 = inl(pm_tmr_ioport);
47	} while ((v1 > v2 && v1 < v3) || (v2 > v3 && v2 < v1)
48		 || (v3 > v1 && v3 < v2));
49
50	/* mask the output to 24 bits */
51	return (v2 & 0xFFFFFF);
52}
53
54static int __init cpufreq_test_tsc(void)
55{
56	u32 now, then, diff;
57	u64 now_tsc, then_tsc, diff_tsc;
58	int i;
59
60	/* the following code snipped is copied from arch/x86/kernel/acpi/boot.c
61	   of Linux v2.6.25. */
62
63	/* detect the location of the ACPI PM Timer */
64	if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID) {
65		/* FADT rev. 2 */
66		if (acpi_gbl_FADT.xpm_timer_block.space_id !=
67		    ACPI_ADR_SPACE_SYSTEM_IO)
68			return 0;
69
70		pm_tmr_ioport = acpi_gbl_FADT.xpm_timer_block.address;
71		/*
72		 * "X" fields are optional extensions to the original V1.0
73		 * fields, so we must selectively expand V1.0 fields if the
74		 * corresponding X field is zero.
75	 	 */
76		if (!pm_tmr_ioport)
77			pm_tmr_ioport = acpi_gbl_FADT.pm_timer_block;
78	} else {
79		/* FADT rev. 1 */
80		pm_tmr_ioport = acpi_gbl_FADT.pm_timer_block;
81	}
82
83	printk(KERN_DEBUG "start--> \n");
84	then = read_pmtmr();
85	then_tsc = rdtsc();
86	for (i=0;i<20;i++) {
87		mdelay(100);
88		now = read_pmtmr();
89		now_tsc = rdtsc();
90		diff = (now - then) & 0xFFFFFF;
91		diff_tsc = now_tsc - then_tsc;
92		printk(KERN_DEBUG "t1: %08u t2: %08u diff_pmtmr: %08u diff_tsc: %016llu\n", then, now, diff, diff_tsc);
93		then = now;
94		then_tsc = now_tsc;
95	}
96	printk(KERN_DEBUG "<-- end \n");
97	return -ENODEV;
98}
99
100static void __exit cpufreq_none(void)
101{
102	return;
103}
104
105module_init(cpufreq_test_tsc)
106module_exit(cpufreq_none)
107
108
109MODULE_AUTHOR("Dominik Brodowski");
110MODULE_DESCRIPTION("Verify the TSC cpufreq notifier working correctly -- needs ACPI-enabled system");
111MODULE_LICENSE ("GPL");
112