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