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