linux-imx

/*

 * linux/drivers/clocksource/acpi_pm.c

 *

 * This file contains the ACPI PM based clocksource.

 *

 * This code was largely moved from the i386 timer_pm.c file

 * which was (C) Dominik Brodowski <linux@brodo.de> 2003

 * and contained the following comments:

 *

 * Driver to use the Power Management Timer (PMTMR) available in some

 * southbridges as primary timing source for the Linux kernel.

 *

 * Based on parts of linux/drivers/acpi/hardware/hwtimer.c, timer_pit.c,

 * timer_hpet.c, and on Arjan van de Ven's implementation for 2.4.

 *

 * This file is licensed under the GPL v2.

 */

​

#include <linux/acpi_pmtmr.h>

#include <linux/clocksource.h>

#include <linux/timex.h>

#include <linux/errno.h>

#include <linux/init.h>

#include <linux/pci.h>

#include <linux/delay.h>

#include <asm/io.h>

​

/*

 * The I/O port the PMTMR resides at.

 * The location is detected during setup_arch(),

 * in arch/i386/kernel/acpi/boot.c

 */

u32 pmtmr_ioport __read_mostly;

​

static inline u32 read_pmtmr(void)

{

    /* mask the output to 24 bits */

    return inl(pmtmr_ioport) & ACPI_PM_MASK;

}

​

u32 acpi_pm_read_verified(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 clock

     * source is not latched, you must read it multiple

     * times to ensure a safe value is read:

     */

    do {

        v1 = read_pmtmr();

        v2 = read_pmtmr();

        v3 = read_pmtmr();

    } while (unlikely((v1 > v2 && v1 < v3) || (v2 > v3 && v2 < v1)

              || (v3 > v1 && v3 < v2)));

​

    return v2;

}

​

static u64 acpi_pm_read(struct clocksource *cs)

{

    return (u64)read_pmtmr();