// SPDX-License-Identifier: GPL-2.0-only
/*
 * 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");