cpufreq-test_tsc.c

  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");