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1// SPDX-License-Identifier: GPL-2.0-only2/*3 * test module to check whether the TSC-based delay routine continues4 * to work properly after cpufreq transitions. Needs ACPI to work5 * properly.6 *7 * Based partly on the Power Management Timer (PMTMR) code to be found8 * in arch/i386/kernel/timers/timer_pm.c on recent 2.6. kernels, especially9 * code written by John Stultz. The read_pmtmr function was copied verbatim10 * from that file.11 *12 * (C) 2004 Dominik Brodowski13 *14 * To use:15 * 1.) pass clock=tsc to the kernel on your bootloader16 * 2.) modprobe this module (it'll fail)17 * 3.) change CPU frequency18 * 4.) modprobe this module again19 * 5.) if the third value, "diff_pmtmr", changes between 2. and 4., the20 * TSC-based delay routine on the Linux kernel does not correctly21 * handle the cpufreq transition. Please report this to22 * linux-pm@vger.kernel.org23 */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 broken39 * chipsets (ICH4, PIIX4 and PIIX4E) where the ACPI PM time40 * source is not latched, so you must read it multiple41 * 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.c61 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 V1.073 * fields, so we must selectively expand V1.0 fields if the74 * 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