/*
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* test module to check whether the TSC-based delay routine continues
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* to work properly after cpufreq transitions. Needs ACPI to work
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* properly.
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*
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* Based partly on the Power Management Timer (PMTMR) code to be found
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* in arch/i386/kernel/timers/timer_pm.c on recent 2.6. kernels, especially
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* code written by John Stultz. The read_pmtmr function was copied verbatim
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* from that file.
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*
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* (C) 2004 Dominik Brodowski
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*
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* To use:
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* 1.) pass clock=tsc to the kernel on your bootloader
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* 2.) modprobe this module (it'll fail)
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* 3.) change CPU frequency
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* 4.) modprobe this module again
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* 5.) if the third value, "diff_pmtmr", changes between 2. and 4., the
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* TSC-based delay routine on the Linux kernel does not correctly
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* handle the cpufreq transition. Please report this to
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* linux-pm@vger.kernel.org
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/delay.h>
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#include <linux/acpi.h>
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#include <asm/io.h>
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static int pm_tmr_ioport = 0;
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/*helper function to safely read acpi pm timesource*/
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static u32 read_pmtmr(void)
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{
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u32 v1=0,v2=0,v3=0;
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/* It has been reported that because of various broken
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* chipsets (ICH4, PIIX4 and PIIX4E) where the ACPI PM time
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* source is not latched, so you must read it multiple
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* times to insure a safe value is read.
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*/
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do {
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v1 = inl(pm_tmr_ioport);
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v2 = inl(pm_tmr_ioport);
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v3 = inl(pm_tmr_ioport);
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} while ((v1 > v2 && v1 < v3) || (v2 > v3 && v2 < v1)
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|| (v3 > v1 && v3 < v2));
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/* mask the output to 24 bits */
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return (v2 & 0xFFFFFF);
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}
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static int __init cpufreq_test_tsc(void)
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{
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u32 now, then, diff;
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u64 now_tsc, then_tsc, diff_tsc;
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int i;
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/* the following code snipped is copied from arch/x86/kernel/acpi/boot.c
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of Linux v2.6.25. */
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/* detect the location of the ACPI PM Timer */
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if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID) {
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/* FADT rev. 2 */
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if (acpi_gbl_FADT.xpm_timer_block.space_id !=
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ACPI_ADR_SPACE_SYSTEM_IO)
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return 0;
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pm_tmr_ioport = acpi_gbl_FADT.xpm_timer_block.address;
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/*
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* "X" fields are optional extensions to the original V1.0
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* fields, so we must selectively expand V1.0 fields if the
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* corresponding X field is zero.
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*/
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if (!pm_tmr_ioport)
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pm_tmr_ioport = acpi_gbl_FADT.pm_timer_block;
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} else {
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/* FADT rev. 1 */
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pm_tmr_ioport = acpi_gbl_FADT.pm_timer_block;
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}
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printk(KERN_DEBUG "start--> \n");
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then = read_pmtmr();
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then_tsc = rdtsc();
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for (i=0;i<20;i++) {
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mdelay(100);
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now = read_pmtmr();
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now_tsc = rdtsc();
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diff = (now - then) & 0xFFFFFF;
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diff_tsc = now_tsc - then_tsc;
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printk(KERN_DEBUG "t1: %08u t2: %08u diff_pmtmr: %08u diff_tsc: %016llu\n", then, now, diff, diff_tsc);
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then = now;
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then_tsc = now_tsc;
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}
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printk(KERN_DEBUG "<-- end \n");
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return -ENODEV;
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}
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static void __exit cpufreq_none(void)
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{
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return;
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}
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module_init(cpufreq_test_tsc)
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module_exit(cpufreq_none)
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MODULE_AUTHOR("Dominik Brodowski");
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MODULE_DESCRIPTION("Verify the TSC cpufreq notifier working correctly -- needs ACPI-enabled system");
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MODULE_LICENSE ("GPL");
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