1. 根目录:
2. drivers
3. clocksource
4. acpi_pm.c

/*
 * 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 cycle_t acpi_pm_read(struct clocksource *cs)
{
	return (cycle_t)read_pmtmr();
}

static struct clocksource clocksource_acpi_pm = {
	.name		= "acpi_pm",
	.rating		= 200,
	.read		= acpi_pm_read,
	.mask		= (cycle_t)ACPI_PM_MASK,
	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
};


#ifdef CONFIG_PCI
static int acpi_pm_good;
static int __init acpi_pm_good_setup(char *__str)
{
	acpi_pm_good = 1;
	return 1;
}
__setup("acpi_pm_good", acpi_pm_good_setup);

static cycle_t acpi_pm_read_slow(struct clocksource *cs)
{
	return (cycle_t)acpi_pm_read_verified();
}

static inline void acpi_pm_need_workaround(void)
{
	clocksource_acpi_pm.read = acpi_pm_read_slow;
	clocksource_acpi_pm.rating = 120;
}

/*
 * PIIX4 Errata:
 *
 * The power management timer may return improper results when read.
 * Although the timer value settles properly after incrementing,
 * while incrementing there is a 3 ns window every 69.8 ns where the
 * timer value is indeterminate (a 4.2% chance that the data will be
 * incorrect when read). As a result, the ACPI free running count up
 * timer specification is violated due to erroneous reads.
 */
static void acpi_pm_check_blacklist(struct pci_dev *dev)
{
	if (acpi_pm_good)
		return;

	/* the bug has been fixed in PIIX4M */
	if (dev->revision < 3) {
		printk(KERN_WARNING "* Found PM-Timer Bug on the chipset."
		       " Due to workarounds for a bug,\n"
		       "* this clock source is slow. Consider trying"
		       " other clock sources\n");

		acpi_pm_need_workaround();
	}
}
DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_82371AB_3,
			acpi_pm_check_blacklist);

static void acpi_pm_check_graylist(struct pci_dev *dev)
{
	if (acpi_pm_good)
		return;

	printk(KERN_WARNING "* The chipset may have PM-Timer Bug. Due to"
	       " workarounds for a bug,\n"
	       "* this clock source is slow. If you are sure your timer"
	       " does not have\n"
	       "* this bug, please use \"acpi_pm_good\" to disable the"
	       " workaround\n");

	acpi_pm_need_workaround();
}
DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_82801DB_0,
			acpi_pm_check_graylist);
DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_SERVERWORKS, PCI_DEVICE_ID_SERVERWORKS_LE,
			acpi_pm_check_graylist);
#endif

#ifndef CONFIG_X86_64
#include <asm/mach_timer.h>
#define PMTMR_EXPECTED_RATE \
  ((CALIBRATE_LATCH * (PMTMR_TICKS_PER_SEC >> 10)) / (PIT_TICK_RATE>>10))
/*
 * Some boards have the PMTMR running way too fast. We check
 * the PMTMR rate against PIT channel 2 to catch these cases.
 */
static int verify_pmtmr_rate(void)
{
	cycle_t value1, value2;
	unsigned long count, delta;

	mach_prepare_counter();
	value1 = clocksource_acpi_pm.read(&clocksource_acpi_pm);
	mach_countup(&count);
	value2 = clocksource_acpi_pm.read(&clocksource_acpi_pm);
	delta = (value2 - value1) & ACPI_PM_MASK;

	/* Check that the PMTMR delta is within 5% of what we expect */
	if (delta < (PMTMR_EXPECTED_RATE * 19) / 20 ||
	    delta > (PMTMR_EXPECTED_RATE * 21) / 20) {
		printk(KERN_INFO "PM-Timer running at invalid rate: %lu%% "
			"of normal - aborting.\n",
			100UL * delta / PMTMR_EXPECTED_RATE);
		return -1;
	}

	return 0;
}
#else
#define verify_pmtmr_rate() (0)
#endif

/* Number of monotonicity checks to perform during initialization */
#define ACPI_PM_MONOTONICITY_CHECKS 10
/* Number of reads we try to get two different values */
#define ACPI_PM_READ_CHECKS 10000

static int __init init_acpi_pm_clocksource(void)
{
	cycle_t value1, value2;
	unsigned int i, j = 0;

	if (!pmtmr_ioport)
		return -ENODEV;

	/* "verify" this timing source: */
	for (j = 0; j < ACPI_PM_MONOTONICITY_CHECKS; j++) {
		udelay(100 * j);
		value1 = clocksource_acpi_pm.read(&clocksource_acpi_pm);
		for (i = 0; i < ACPI_PM_READ_CHECKS; i++) {
			value2 = clocksource_acpi_pm.read(&clocksource_acpi_pm);
			if (value2 == value1)
				continue;
			if (value2 > value1)
				break;
			if ((value2 < value1) && ((value2) < 0xFFF))
				break;
			printk(KERN_INFO "PM-Timer had inconsistent results:"
			       " %#llx, %#llx - aborting.\n",
			       value1, value2);
			pmtmr_ioport = 0;
			return -EINVAL;
		}
		if (i == ACPI_PM_READ_CHECKS) {
			printk(KERN_INFO "PM-Timer failed consistency check "
			       " (%#llx) - aborting.\n", value1);
			pmtmr_ioport = 0;
			return -ENODEV;
		}
	}

	if (verify_pmtmr_rate() != 0){
		pmtmr_ioport = 0;
		return -ENODEV;
	}

	return clocksource_register_hz(&clocksource_acpi_pm,
						PMTMR_TICKS_PER_SEC);
}

/* We use fs_initcall because we want the PCI fixups to have run
 * but we still need to load before device_initcall
 */
fs_initcall(init_acpi_pm_clocksource);

/*
 * Allow an override of the IOPort. Stupid BIOSes do not tell us about
 * the PMTimer, but we might know where it is.
 */
static int __init parse_pmtmr(char *arg)
{
	unsigned int base;
	int ret;

	ret = kstrtouint(arg, 16, &base);
	if (ret)
		return ret;

	pr_info("PMTMR IOPort override: 0x%04x -> 0x%04x\n", pmtmr_ioport,
		base);
	pmtmr_ioport = base;

	return 1;
}
__setup("pmtmr=", parse_pmtmr);