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 
32 static int pm_tmr_ioport = 0;
33 
34 /*helper function to safely read acpi pm timesource*/
read_pmtmr(void)35 static 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 
cpufreq_test_tsc(void)54 static 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 
cpufreq_none(void)100 static void __exit cpufreq_none(void)
101 {
102 	return;
103 }
104 
105 module_init(cpufreq_test_tsc)
106 module_exit(cpufreq_none)
107 
108 
109 MODULE_AUTHOR("Dominik Brodowski");
110 MODULE_DESCRIPTION("Verify the TSC cpufreq notifier working correctly -- needs ACPI-enabled system");
111 MODULE_LICENSE ("GPL");
112