x86, tsc: Fix SMI induced variation in quick_pit_calibrate()

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / arch / x86 / kernel / hpet.c

#include <linux/clocksource.h>
#include <linux/clockchips.h>
#include <linux/interrupt.h>
#include <linux/export.h>
#include <linux/sysdev.h>
#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/i8253.h>
#include <linux/slab.h>
#include <linux/hpet.h>
#include <linux/init.h>
#include <linux/cpu.h>
#include <linux/pm.h>
#include <linux/io.h>

#include <asm/fixmap.h>
#include <asm/hpet.h>
#include <asm/time.h>

#define HPET_MASK                       CLOCKSOURCE_MASK(32)

/* FSEC = 10^-15
   NSEC = 10^-9 */
#define FSEC_PER_NSEC                   1000000L

#define HPET_DEV_USED_BIT               2
#define HPET_DEV_USED                   (1 << HPET_DEV_USED_BIT)
#define HPET_DEV_VALID                  0x8
#define HPET_DEV_FSB_CAP                0x1000
#define HPET_DEV_PERI_CAP               0x2000

#define HPET_MIN_CYCLES                 128
#define HPET_MIN_PROG_DELTA             (HPET_MIN_CYCLES + (HPET_MIN_CYCLES >> 1))

/*
 * HPET address is set in acpi/boot.c, when an ACPI entry exists
 */
unsigned long                           hpet_address;
u8                                      hpet_blockid; /* OS timer block num */
u8                                      hpet_msi_disable;

#ifdef CONFIG_PCI_MSI
static unsigned long                    hpet_num_timers;
#endif
static void __iomem                     *hpet_virt_address;

struct hpet_dev {
        struct clock_event_device       evt;
        unsigned int                    num;
        int                             cpu;
        unsigned int                    irq;
        unsigned int                    flags;
        char                            name[10];
};

inline struct hpet_dev *EVT_TO_HPET_DEV(struct clock_event_device *evtdev)
{
        return container_of(evtdev, struct hpet_dev, evt);
}

inline unsigned int hpet_readl(unsigned int a)
{
        return readl(hpet_virt_address + a);
}

static inline void hpet_writel(unsigned int d, unsigned int a)
{
        writel(d, hpet_virt_address + a);
}

#ifdef CONFIG_X86_64
#include <asm/pgtable.h>
#endif

static inline void hpet_set_mapping(void)
{
        hpet_virt_address = ioremap_nocache(hpet_address, HPET_MMAP_SIZE);
#ifdef CONFIG_X86_64
        __set_fixmap(VSYSCALL_HPET, hpet_address, PAGE_KERNEL_VVAR_NOCACHE);
#endif
}

static inline void hpet_clear_mapping(void)
{
        iounmap(hpet_virt_address);
        hpet_virt_address = NULL;
}

/*
 * HPET command line enable / disable
 */
static int boot_hpet_disable;
int hpet_force_user;
static int hpet_verbose;

static int __init hpet_setup(char *str)
{
        if (str) {
                if (!strncmp("disable", str, 7))
                        boot_hpet_disable = 1;
                if (!strncmp("force", str, 5))
                        hpet_force_user = 1;
                if (!strncmp("verbose", str, 7))
                        hpet_verbose = 1;
        }
        return 1;
}
__setup("hpet=", hpet_setup);

static int __init disable_hpet(char *str)
{
        boot_hpet_disable = 1;
        return 1;
}
__setup("nohpet", disable_hpet);

static inline int is_hpet_capable(void)
{
        return !boot_hpet_disable && hpet_address;
}

/*
 * HPET timer interrupt enable / disable
 */
static int hpet_legacy_int_enabled;

/**
 * is_hpet_enabled - check whether the hpet timer interrupt is enabled
 */
int is_hpet_enabled(void)
{
        return is_hpet_capable() && hpet_legacy_int_enabled;
}
EXPORT_SYMBOL_GPL(is_hpet_enabled);

static void _hpet_print_config(const char *function, int line)
{
        u32 i, timers, l, h;
        printk(KERN_INFO "hpet: %s(%d):\n", function, line);
        l = hpet_readl(HPET_ID);
        h = hpet_readl(HPET_PERIOD);
        timers = ((l & HPET_ID_NUMBER) >> HPET_ID_NUMBER_SHIFT) + 1;
        printk(KERN_INFO "hpet: ID: 0x%x, PERIOD: 0x%x\n", l, h);
        l = hpet_readl(HPET_CFG);
        h = hpet_readl(HPET_STATUS);
        printk(KERN_INFO "hpet: CFG: 0x%x, STATUS: 0x%x\n", l, h);
        l = hpet_readl(HPET_COUNTER);
        h = hpet_readl(HPET_COUNTER+4);
        printk(KERN_INFO "hpet: COUNTER_l: 0x%x, COUNTER_h: 0x%x\n", l, h);

        for (i = 0; i < timers; i++) {
                l = hpet_readl(HPET_Tn_CFG(i));
                h = hpet_readl(HPET_Tn_CFG(i)+4);
                printk(KERN_INFO "hpet: T%d: CFG_l: 0x%x, CFG_h: 0x%x\n",
                       i, l, h);
                l = hpet_readl(HPET_Tn_CMP(i));
                h = hpet_readl(HPET_Tn_CMP(i)+4);
                printk(KERN_INFO "hpet: T%d: CMP_l: 0x%x, CMP_h: 0x%x\n",
                       i, l, h);
                l = hpet_readl(HPET_Tn_ROUTE(i));
                h = hpet_readl(HPET_Tn_ROUTE(i)+4);
                printk(KERN_INFO "hpet: T%d ROUTE_l: 0x%x, ROUTE_h: 0x%x\n",
                       i, l, h);
        }
}

#define hpet_print_config()                                     \
do {                                                            \
        if (hpet_verbose)                                       \
                _hpet_print_config(__FUNCTION__, __LINE__);     \
} while (0)

/*
 * When the hpet driver (/dev/hpet) is enabled, we need to reserve
 * timer 0 and timer 1 in case of RTC emulation.
 */
#ifdef CONFIG_HPET

static void hpet_reserve_msi_timers(struct hpet_data *hd);

static void hpet_reserve_platform_timers(unsigned int id)
{
        struct hpet __iomem *hpet = hpet_virt_address;
        struct hpet_timer __iomem *timer = &hpet->hpet_timers[2];
        unsigned int nrtimers, i;
        struct hpet_data hd;

        nrtimers = ((id & HPET_ID_NUMBER) >> HPET_ID_NUMBER_SHIFT) + 1;

        memset(&hd, 0, sizeof(hd));
        hd.hd_phys_address      = hpet_address;
        hd.hd_address           = hpet;
        hd.hd_nirqs             = nrtimers;
        hpet_reserve_timer(&hd, 0);

#ifdef CONFIG_HPET_EMULATE_RTC
        hpet_reserve_timer(&hd, 1);
#endif

        /*
         * NOTE that hd_irq[] reflects IOAPIC input pins (LEGACY_8254
         * is wrong for i8259!) not the output IRQ.  Many BIOS writers
         * don't bother configuring *any* comparator interrupts.
         */
        hd.hd_irq[0] = HPET_LEGACY_8254;
        hd.hd_irq[1] = HPET_LEGACY_RTC;

        for (i = 2; i < nrtimers; timer++, i++) {
                hd.hd_irq[i] = (readl(&timer->hpet_config) &
                        Tn_INT_ROUTE_CNF_MASK) >> Tn_INT_ROUTE_CNF_SHIFT;
        }

        hpet_reserve_msi_timers(&hd);

        hpet_alloc(&hd);

}
#else
static void hpet_reserve_platform_timers(unsigned int id) { }
#endif

/*
 * Common hpet info
 */
static unsigned long hpet_freq;

static void hpet_legacy_set_mode(enum clock_event_mode mode,
                          struct clock_event_device *evt);
static int hpet_legacy_next_event(unsigned long delta,
                           struct clock_event_device *evt);

/*
 * The hpet clock event device
 */
static struct clock_event_device hpet_clockevent = {
        .name           = "hpet",
        .features       = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
        .set_mode       = hpet_legacy_set_mode,
        .set_next_event = hpet_legacy_next_event,
        .irq            = 0,
        .rating         = 50,
};

static void hpet_stop_counter(void)
{
        unsigned long cfg = hpet_readl(HPET_CFG);
        cfg &= ~HPET_CFG_ENABLE;
        hpet_writel(cfg, HPET_CFG);
}

static void hpet_reset_counter(void)
{
        hpet_writel(0, HPET_COUNTER);
        hpet_writel(0, HPET_COUNTER + 4);
}

static void hpet_start_counter(void)
{
        unsigned int cfg = hpet_readl(HPET_CFG);
        cfg |= HPET_CFG_ENABLE;
        hpet_writel(cfg, HPET_CFG);
}

static void hpet_restart_counter(void)
{
        hpet_stop_counter();
        hpet_reset_counter();
        hpet_start_counter();
}

static void hpet_resume_device(void)
{
        force_hpet_resume();
}

static void hpet_resume_counter(struct clocksource *cs)
{
        hpet_resume_device();
        hpet_restart_counter();
}

static void hpet_enable_legacy_int(void)
{
        unsigned int cfg = hpet_readl(HPET_CFG);

        cfg |= HPET_CFG_LEGACY;
        hpet_writel(cfg, HPET_CFG);
        hpet_legacy_int_enabled = 1;
}

static void hpet_legacy_clockevent_register(void)
{
        /* Start HPET legacy interrupts */
        hpet_enable_legacy_int();

        /*
         * Start hpet with the boot cpu mask and make it
         * global after the IO_APIC has been initialized.
         */
        hpet_clockevent.cpumask = cpumask_of(smp_processor_id());
        clockevents_config_and_register(&hpet_clockevent, hpet_freq,
                                        HPET_MIN_PROG_DELTA, 0x7FFFFFFF);
        global_clock_event = &hpet_clockevent;
        printk(KERN_DEBUG "hpet clockevent registered\n");
}

static int hpet_setup_msi_irq(unsigned int irq);

static void hpet_set_mode(enum clock_event_mode mode,
                          struct clock_event_device *evt, int timer)
{
        unsigned int cfg, cmp, now;
        uint64_t delta;

        switch (mode) {
        case CLOCK_EVT_MODE_PERIODIC:
                hpet_stop_counter();
                delta = ((uint64_t)(NSEC_PER_SEC/HZ)) * evt->mult;
                delta >>= evt->shift;
                now = hpet_readl(HPET_COUNTER);
                cmp = now + (unsigned int) delta;
                cfg = hpet_readl(HPET_Tn_CFG(timer));
                /* Make sure we use edge triggered interrupts */
                cfg &= ~HPET_TN_LEVEL;
                cfg |= HPET_TN_ENABLE | HPET_TN_PERIODIC |
                       HPET_TN_SETVAL | HPET_TN_32BIT;
                hpet_writel(cfg, HPET_Tn_CFG(timer));
                hpet_writel(cmp, HPET_Tn_CMP(timer));
                udelay(1);
                /*
                 * HPET on AMD 81xx needs a second write (with HPET_TN_SETVAL
                 * cleared) to T0_CMP to set the period. The HPET_TN_SETVAL
                 * bit is automatically cleared after the first write.
                 * (See AMD-8111 HyperTransport I/O Hub Data Sheet,
                 * Publication # 24674)
                 */
                hpet_writel((unsigned int) delta, HPET_Tn_CMP(timer));
                hpet_start_counter();
                hpet_print_config();
                break;

        case CLOCK_EVT_MODE_ONESHOT:
                cfg = hpet_readl(HPET_Tn_CFG(timer));
                cfg &= ~HPET_TN_PERIODIC;
                cfg |= HPET_TN_ENABLE | HPET_TN_32BIT;
                hpet_writel(cfg, HPET_Tn_CFG(timer));
                break;

        case CLOCK_EVT_MODE_UNUSED:
        case CLOCK_EVT_MODE_SHUTDOWN:
                cfg = hpet_readl(HPET_Tn_CFG(timer));
                cfg &= ~HPET_TN_ENABLE;
                hpet_writel(cfg, HPET_Tn_CFG(timer));
                break;

        case CLOCK_EVT_MODE_RESUME:
                if (timer == 0) {
                        hpet_enable_legacy_int();
                } else {
                        struct hpet_dev *hdev = EVT_TO_HPET_DEV(evt);
                        hpet_setup_msi_irq(hdev->irq);
                        disable_irq(hdev->irq);
                        irq_set_affinity(hdev->irq, cpumask_of(hdev->cpu));
                        enable_irq(hdev->irq);
                }
                hpet_print_config();
                break;
        }
}

static int hpet_next_event(unsigned long delta,
                           struct clock_event_device *evt, int timer)
{
        u32 cnt;
        s32 res;

        cnt = hpet_readl(HPET_COUNTER);
        cnt += (u32) delta;
        hpet_writel(cnt, HPET_Tn_CMP(timer));

        /*
         * HPETs are a complete disaster. The compare register is
         * based on a equal comparison and neither provides a less
         * than or equal functionality (which would require to take
         * the wraparound into account) nor a simple count down event
         * mode. Further the write to the comparator register is
         * delayed internally up to two HPET clock cycles in certain
         * chipsets (ATI, ICH9,10). Some newer AMD chipsets have even
         * longer delays. We worked around that by reading back the
         * compare register, but that required another workaround for
         * ICH9,10 chips where the first readout after write can
         * return the old stale value. We already had a minimum
         * programming delta of 5us enforced, but a NMI or SMI hitting
         * between the counter readout and the comparator write can
         * move us behind that point easily. Now instead of reading
         * the compare register back several times, we make the ETIME
         * decision based on the following: Return ETIME if the
         * counter value after the write is less than HPET_MIN_CYCLES
         * away from the event or if the counter is already ahead of
         * the event. The minimum programming delta for the generic
         * clockevents code is set to 1.5 * HPET_MIN_CYCLES.
         */
        res = (s32)(cnt - hpet_readl(HPET_COUNTER));

        return res < HPET_MIN_CYCLES ? -ETIME : 0;
}

static void hpet_legacy_set_mode(enum clock_event_mode mode,
                        struct clock_event_device *evt)
{
        hpet_set_mode(mode, evt, 0);
}

static int hpet_legacy_next_event(unsigned long delta,
                        struct clock_event_device *evt)
{
        return hpet_next_event(delta, evt, 0);
}

/*
 * HPET MSI Support
 */
#ifdef CONFIG_PCI_MSI

static DEFINE_PER_CPU(struct hpet_dev *, cpu_hpet_dev);
static struct hpet_dev  *hpet_devs;

void hpet_msi_unmask(struct irq_data *data)
{
        struct hpet_dev *hdev = data->handler_data;
        unsigned int cfg;

        /* unmask it */
        cfg = hpet_readl(HPET_Tn_CFG(hdev->num));
        cfg |= HPET_TN_FSB;
        hpet_writel(cfg, HPET_Tn_CFG(hdev->num));
}

void hpet_msi_mask(struct irq_data *data)
{
        struct hpet_dev *hdev = data->handler_data;
        unsigned int cfg;

        /* mask it */
        cfg = hpet_readl(HPET_Tn_CFG(hdev->num));
        cfg &= ~HPET_TN_FSB;
        hpet_writel(cfg, HPET_Tn_CFG(hdev->num));
}

void hpet_msi_write(struct hpet_dev *hdev, struct msi_msg *msg)
{
        hpet_writel(msg->data, HPET_Tn_ROUTE(hdev->num));
        hpet_writel(msg->address_lo, HPET_Tn_ROUTE(hdev->num) + 4);
}

void hpet_msi_read(struct hpet_dev *hdev, struct msi_msg *msg)
{
        msg->data = hpet_readl(HPET_Tn_ROUTE(hdev->num));
        msg->address_lo = hpet_readl(HPET_Tn_ROUTE(hdev->num) + 4);
        msg->address_hi = 0;
}

static void hpet_msi_set_mode(enum clock_event_mode mode,
                                struct clock_event_device *evt)
{
        struct hpet_dev *hdev = EVT_TO_HPET_DEV(evt);
        hpet_set_mode(mode, evt, hdev->num);
}

static int hpet_msi_next_event(unsigned long delta,
                                struct clock_event_device *evt)
{
        struct hpet_dev *hdev = EVT_TO_HPET_DEV(evt);
        return hpet_next_event(delta, evt, hdev->num);
}

static int hpet_setup_msi_irq(unsigned int irq)
{
        if (arch_setup_hpet_msi(irq, hpet_blockid)) {
                destroy_irq(irq);
                return -EINVAL;
        }
        return 0;
}

static int hpet_assign_irq(struct hpet_dev *dev)
{
        unsigned int irq;

        irq = create_irq_nr(0, -1);
        if (!irq)
                return -EINVAL;

        irq_set_handler_data(irq, dev);

        if (hpet_setup_msi_irq(irq))
                return -EINVAL;

        dev->irq = irq;
        return 0;
}

static irqreturn_t hpet_interrupt_handler(int irq, void *data)
{
        struct hpet_dev *dev = (struct hpet_dev *)data;
        struct clock_event_device *hevt = &dev->evt;

        if (!hevt->event_handler) {
                printk(KERN_INFO "Spurious HPET timer interrupt on HPET timer %d\n",
                                dev->num);
                return IRQ_HANDLED;
        }

        hevt->event_handler(hevt);
        return IRQ_HANDLED;
}

static int hpet_setup_irq(struct hpet_dev *dev)
{

        if (request_irq(dev->irq, hpet_interrupt_handler,
                        IRQF_TIMER | IRQF_DISABLED | IRQF_NOBALANCING,
                        dev->name, dev))
                return -1;

        disable_irq(dev->irq);
        irq_set_affinity(dev->irq, cpumask_of(dev->cpu));
        enable_irq(dev->irq);

        printk(KERN_DEBUG "hpet: %s irq %d for MSI\n",
                         dev->name, dev->irq);

        return 0;
}

/* This should be called in specific @cpu */
static void init_one_hpet_msi_clockevent(struct hpet_dev *hdev, int cpu)
{
        struct clock_event_device *evt = &hdev->evt;

        WARN_ON(cpu != smp_processor_id());
        if (!(hdev->flags & HPET_DEV_VALID))
                return;

        if (hpet_setup_msi_irq(hdev->irq))
                return;

        hdev->cpu = cpu;
        per_cpu(cpu_hpet_dev, cpu) = hdev;
        evt->name = hdev->name;
        hpet_setup_irq(hdev);
        evt->irq = hdev->irq;

        evt->rating = 110;
        evt->features = CLOCK_EVT_FEAT_ONESHOT;
        if (hdev->flags & HPET_DEV_PERI_CAP)
                evt->features |= CLOCK_EVT_FEAT_PERIODIC;

        evt->set_mode = hpet_msi_set_mode;
        evt->set_next_event = hpet_msi_next_event;
        evt->cpumask = cpumask_of(hdev->cpu);

        clockevents_config_and_register(evt, hpet_freq, HPET_MIN_PROG_DELTA,
                                        0x7FFFFFFF);
}

#ifdef CONFIG_HPET
/* Reserve at least one timer for userspace (/dev/hpet) */
#define RESERVE_TIMERS 1
#else
#define RESERVE_TIMERS 0
#endif

static void hpet_msi_capability_lookup(unsigned int start_timer)
{
        unsigned int id;
        unsigned int num_timers;
        unsigned int num_timers_used = 0;
        int i;

        if (hpet_msi_disable)
                return;

        if (boot_cpu_has(X86_FEATURE_ARAT))
                return;
        id = hpet_readl(HPET_ID);

        num_timers = ((id & HPET_ID_NUMBER) >> HPET_ID_NUMBER_SHIFT);
        num_timers++; /* Value read out starts from 0 */
        hpet_print_config();

        hpet_devs = kzalloc(sizeof(struct hpet_dev) * num_timers, GFP_KERNEL);
        if (!hpet_devs)
                return;

        hpet_num_timers = num_timers;

        for (i = start_timer; i < num_timers - RESERVE_TIMERS; i++) {
                struct hpet_dev *hdev = &hpet_devs[num_timers_used];
                unsigned int cfg = hpet_readl(HPET_Tn_CFG(i));

                /* Only consider HPET timer with MSI support */
                if (!(cfg & HPET_TN_FSB_CAP))
                        continue;

                hdev->flags = 0;
                if (cfg & HPET_TN_PERIODIC_CAP)
                        hdev->flags |= HPET_DEV_PERI_CAP;
                hdev->num = i;

                sprintf(hdev->name, "hpet%d", i);
                if (hpet_assign_irq(hdev))
                        continue;

                hdev->flags |= HPET_DEV_FSB_CAP;
                hdev->flags |= HPET_DEV_VALID;
                num_timers_used++;
                if (num_timers_used == num_possible_cpus())
                        break;
        }

        printk(KERN_INFO "HPET: %d timers in total, %d timers will be used for per-cpu timer\n",
                num_timers, num_timers_used);
}

#ifdef CONFIG_HPET
static void hpet_reserve_msi_timers(struct hpet_data *hd)
{
        int i;

        if (!hpet_devs)
                return;

        for (i = 0; i < hpet_num_timers; i++) {
                struct hpet_dev *hdev = &hpet_devs[i];

                if (!(hdev->flags & HPET_DEV_VALID))
                        continue;

                hd->hd_irq[hdev->num] = hdev->irq;
                hpet_reserve_timer(hd, hdev->num);
        }
}
#endif

static struct hpet_dev *hpet_get_unused_timer(void)
{
        int i;

        if (!hpet_devs)
                return NULL;

        for (i = 0; i < hpet_num_timers; i++) {
                struct hpet_dev *hdev = &hpet_devs[i];

                if (!(hdev->flags & HPET_DEV_VALID))
                        continue;
                if (test_and_set_bit(HPET_DEV_USED_BIT,
                        (unsigned long *)&hdev->flags))
                        continue;
                return hdev;
        }
        return NULL;
}

struct hpet_work_struct {
        struct delayed_work work;
        struct completion complete;
};

static void hpet_work(struct work_struct *w)
{
        struct hpet_dev *hdev;
        int cpu = smp_processor_id();
        struct hpet_work_struct *hpet_work;

        hpet_work = container_of(w, struct hpet_work_struct, work.work);

        hdev = hpet_get_unused_timer();
        if (hdev)
                init_one_hpet_msi_clockevent(hdev, cpu);

        complete(&hpet_work->complete);
}

static int hpet_cpuhp_notify(struct notifier_block *n,
                unsigned long action, void *hcpu)
{
        unsigned long cpu = (unsigned long)hcpu;
        struct hpet_work_struct work;
        struct hpet_dev *hdev = per_cpu(cpu_hpet_dev, cpu);

        switch (action & 0xf) {
        case CPU_ONLINE:
                INIT_DELAYED_WORK_ONSTACK(&work.work, hpet_work);
                init_completion(&work.complete);
                /* FIXME: add schedule_work_on() */
                schedule_delayed_work_on(cpu, &work.work, 0);
                wait_for_completion(&work.complete);
                destroy_timer_on_stack(&work.work.timer);
                break;
        case CPU_DEAD:
                if (hdev) {
                        free_irq(hdev->irq, hdev);
                        hdev->flags &= ~HPET_DEV_USED;
                        per_cpu(cpu_hpet_dev, cpu) = NULL;
                }
                break;
        }
        return NOTIFY_OK;
}
#else

static int hpet_setup_msi_irq(unsigned int irq)
{
        return 0;
}
static void hpet_msi_capability_lookup(unsigned int start_timer)
{
        return;
}

#ifdef CONFIG_HPET
static void hpet_reserve_msi_timers(struct hpet_data *hd)
{
        return;
}
#endif

static int hpet_cpuhp_notify(struct notifier_block *n,
                unsigned long action, void *hcpu)
{
        return NOTIFY_OK;
}

#endif

/*
 * Clock source related code
 */
static cycle_t read_hpet(struct clocksource *cs)
{
        return (cycle_t)hpet_readl(HPET_COUNTER);
}

static struct clocksource clocksource_hpet = {
        .name           = "hpet",
        .rating         = 250,
        .read           = read_hpet,
        .mask           = HPET_MASK,
        .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
        .resume         = hpet_resume_counter,
#ifdef CONFIG_X86_64
        .archdata       = { .vclock_mode = VCLOCK_HPET },
#endif
};

static int hpet_clocksource_register(void)
{
        u64 start, now;
        cycle_t t1;

        /* Start the counter */
        hpet_restart_counter();

        /* Verify whether hpet counter works */
        t1 = hpet_readl(HPET_COUNTER);
        rdtscll(start);

        /*
         * We don't know the TSC frequency yet, but waiting for
         * 200000 TSC cycles is safe:
         * 4 GHz == 50us
         * 1 GHz == 200us
         */
        do {
                rep_nop();
                rdtscll(now);
        } while ((now - start) < 200000UL);

        if (t1 == hpet_readl(HPET_COUNTER)) {
                printk(KERN_WARNING
                       "HPET counter not counting. HPET disabled\n");
                return -ENODEV;
        }

        clocksource_register_hz(&clocksource_hpet, (u32)hpet_freq);
        return 0;
}

/**
 * hpet_enable - Try to setup the HPET timer. Returns 1 on success.
 */
int __init hpet_enable(void)
{
        unsigned long hpet_period;
        unsigned int id;
        u64 freq;
        int i;

        if (!is_hpet_capable())
                return 0;

        hpet_set_mapping();

        /*
         * Read the period and check for a sane value:
         */
        hpet_period = hpet_readl(HPET_PERIOD);

        /*
         * AMD SB700 based systems with spread spectrum enabled use a
         * SMM based HPET emulation to provide proper frequency
         * setting. The SMM code is initialized with the first HPET
         * register access and takes some time to complete. During
         * this time the config register reads 0xffffffff. We check
         * for max. 1000 loops whether the config register reads a non
         * 0xffffffff value to make sure that HPET is up and running
         * before we go further. A counting loop is safe, as the HPET
         * access takes thousands of CPU cycles. On non SB700 based
         * machines this check is only done once and has no side
         * effects.
         */
        for (i = 0; hpet_readl(HPET_CFG) == 0xFFFFFFFF; i++) {
                if (i == 1000) {
                        printk(KERN_WARNING
                               "HPET config register value = 0xFFFFFFFF. "
                               "Disabling HPET\n");
                        goto out_nohpet;
                }
        }

        if (hpet_period < HPET_MIN_PERIOD || hpet_period > HPET_MAX_PERIOD)
                goto out_nohpet;

        /*
         * The period is a femto seconds value. Convert it to a
         * frequency.
         */
        freq = FSEC_PER_SEC;
        do_div(freq, hpet_period);
        hpet_freq = freq;

        /*
         * Read the HPET ID register to retrieve the IRQ routing
         * information and the number of channels
         */
        id = hpet_readl(HPET_ID);
        hpet_print_config();

#ifdef CONFIG_HPET_EMULATE_RTC
        /*
         * The legacy routing mode needs at least two channels, tick timer
         * and the rtc emulation channel.
         */
        if (!(id & HPET_ID_NUMBER))
                goto out_nohpet;
#endif

        if (hpet_clocksource_register())
                goto out_nohpet;

        if (id & HPET_ID_LEGSUP) {
                hpet_legacy_clockevent_register();
                return 1;
        }
        return 0;

out_nohpet:
        hpet_clear_mapping();
        hpet_address = 0;
        return 0;
}

/*
 * Needs to be late, as the reserve_timer code calls kalloc !
 *
 * Not a problem on i386 as hpet_enable is called from late_time_init,
 * but on x86_64 it is necessary !
 */
static __init int hpet_late_init(void)
{
        int cpu;

        if (boot_hpet_disable)
                return -ENODEV;

        if (!hpet_address) {
                if (!force_hpet_address)
                        return -ENODEV;

                hpet_address = force_hpet_address;
                hpet_enable();
        }

        if (!hpet_virt_address)
                return -ENODEV;

        if (hpet_readl(HPET_ID) & HPET_ID_LEGSUP)
                hpet_msi_capability_lookup(2);
        else
                hpet_msi_capability_lookup(0);

        hpet_reserve_platform_timers(hpet_readl(HPET_ID));
        hpet_print_config();

        if (hpet_msi_disable)
                return 0;

        if (boot_cpu_has(X86_FEATURE_ARAT))
                return 0;

        for_each_online_cpu(cpu) {
                hpet_cpuhp_notify(NULL, CPU_ONLINE, (void *)(long)cpu);
        }

        /* This notifier should be called after workqueue is ready */
        hotcpu_notifier(hpet_cpuhp_notify, -20);

        return 0;
}
fs_initcall(hpet_late_init);

void hpet_disable(void)
{
        if (is_hpet_capable() && hpet_virt_address) {
                unsigned int cfg = hpet_readl(HPET_CFG);

                if (hpet_legacy_int_enabled) {
                        cfg &= ~HPET_CFG_LEGACY;
                        hpet_legacy_int_enabled = 0;
                }
                cfg &= ~HPET_CFG_ENABLE;
                hpet_writel(cfg, HPET_CFG);
        }
}

#ifdef CONFIG_HPET_EMULATE_RTC

/* HPET in LegacyReplacement Mode eats up RTC interrupt line. When, HPET
 * is enabled, we support RTC interrupt functionality in software.
 * RTC has 3 kinds of interrupts:
 * 1) Update Interrupt - generate an interrupt, every sec, when RTC clock
 *    is updated
 * 2) Alarm Interrupt - generate an interrupt at a specific time of day
 * 3) Periodic Interrupt - generate periodic interrupt, with frequencies
 *    2Hz-8192Hz (2Hz-64Hz for non-root user) (all freqs in powers of 2)
 * (1) and (2) above are implemented using polling at a frequency of
 * 64 Hz. The exact frequency is a tradeoff between accuracy and interrupt
 * overhead. (DEFAULT_RTC_INT_FREQ)
 * For (3), we use interrupts at 64Hz or user specified periodic
 * frequency, whichever is higher.
 */
#include <linux/mc146818rtc.h>
#include <linux/rtc.h>
#include <asm/rtc.h>

#define DEFAULT_RTC_INT_FREQ    64
#define DEFAULT_RTC_SHIFT       6
#define RTC_NUM_INTS            1

static unsigned long hpet_rtc_flags;
static int hpet_prev_update_sec;
static struct rtc_time hpet_alarm_time;
static unsigned long hpet_pie_count;
static u32 hpet_t1_cmp;
static u32 hpet_default_delta;
static u32 hpet_pie_delta;
static unsigned long hpet_pie_limit;

static rtc_irq_handler irq_handler;

/*
 * Check that the hpet counter c1 is ahead of the c2
 */
static inline int hpet_cnt_ahead(u32 c1, u32 c2)
{
        return (s32)(c2 - c1) < 0;
}

/*
 * Registers a IRQ handler.
 */
int hpet_register_irq_handler(rtc_irq_handler handler)
{
        if (!is_hpet_enabled())
                return -ENODEV;
        if (irq_handler)
                return -EBUSY;

        irq_handler = handler;

        return 0;
}
EXPORT_SYMBOL_GPL(hpet_register_irq_handler);

/*
 * Deregisters the IRQ handler registered with hpet_register_irq_handler()
 * and does cleanup.
 */
void hpet_unregister_irq_handler(rtc_irq_handler handler)
{
        if (!is_hpet_enabled())
                return;

        irq_handler = NULL;
        hpet_rtc_flags = 0;
}
EXPORT_SYMBOL_GPL(hpet_unregister_irq_handler);

/*
 * Timer 1 for RTC emulation. We use one shot mode, as periodic mode
 * is not supported by all HPET implementations for timer 1.
 *
 * hpet_rtc_timer_init() is called when the rtc is initialized.
 */
int hpet_rtc_timer_init(void)
{
        unsigned int cfg, cnt, delta;
        unsigned long flags;

        if (!is_hpet_enabled())
                return 0;

        if (!hpet_default_delta) {
                uint64_t clc;

                clc = (uint64_t) hpet_clockevent.mult * NSEC_PER_SEC;
                clc >>= hpet_clockevent.shift + DEFAULT_RTC_SHIFT;
                hpet_default_delta = clc;
        }

        if (!(hpet_rtc_flags & RTC_PIE) || hpet_pie_limit)
                delta = hpet_default_delta;
        else
                delta = hpet_pie_delta;

        local_irq_save(flags);

        cnt = delta + hpet_readl(HPET_COUNTER);
        hpet_writel(cnt, HPET_T1_CMP);
        hpet_t1_cmp = cnt;

        cfg = hpet_readl(HPET_T1_CFG);
        cfg &= ~HPET_TN_PERIODIC;
        cfg |= HPET_TN_ENABLE | HPET_TN_32BIT;
        hpet_writel(cfg, HPET_T1_CFG);

        local_irq_restore(flags);

        return 1;
}
EXPORT_SYMBOL_GPL(hpet_rtc_timer_init);

static void hpet_disable_rtc_channel(void)
{
        unsigned long cfg;
        cfg = hpet_readl(HPET_T1_CFG);
        cfg &= ~HPET_TN_ENABLE;
        hpet_writel(cfg, HPET_T1_CFG);
}

/*
 * The functions below are called from rtc driver.
 * Return 0 if HPET is not being used.
 * Otherwise do the necessary changes and return 1.
 */
int hpet_mask_rtc_irq_bit(unsigned long bit_mask)
{
        if (!is_hpet_enabled())
                return 0;

        hpet_rtc_flags &= ~bit_mask;
        if (unlikely(!hpet_rtc_flags))
                hpet_disable_rtc_channel();

        return 1;
}
EXPORT_SYMBOL_GPL(hpet_mask_rtc_irq_bit);

int hpet_set_rtc_irq_bit(unsigned long bit_mask)
{
        unsigned long oldbits = hpet_rtc_flags;

        if (!is_hpet_enabled())
                return 0;

        hpet_rtc_flags |= bit_mask;

        if ((bit_mask & RTC_UIE) && !(oldbits & RTC_UIE))
                hpet_prev_update_sec = -1;

        if (!oldbits)
                hpet_rtc_timer_init();

        return 1;
}
EXPORT_SYMBOL_GPL(hpet_set_rtc_irq_bit);

int hpet_set_alarm_time(unsigned char hrs, unsigned char min,
                        unsigned char sec)
{
        if (!is_hpet_enabled())
                return 0;

        hpet_alarm_time.tm_hour = hrs;
        hpet_alarm_time.tm_min = min;
        hpet_alarm_time.tm_sec = sec;

        return 1;
}
EXPORT_SYMBOL_GPL(hpet_set_alarm_time);

int hpet_set_periodic_freq(unsigned long freq)
{
        uint64_t clc;

        if (!is_hpet_enabled())
                return 0;

        if (freq <= DEFAULT_RTC_INT_FREQ)
                hpet_pie_limit = DEFAULT_RTC_INT_FREQ / freq;
        else {
                clc = (uint64_t) hpet_clockevent.mult * NSEC_PER_SEC;
                do_div(clc, freq);
                clc >>= hpet_clockevent.shift;
                hpet_pie_delta = clc;
                hpet_pie_limit = 0;
        }
        return 1;
}
EXPORT_SYMBOL_GPL(hpet_set_periodic_freq);

int hpet_rtc_dropped_irq(void)
{
        return is_hpet_enabled();
}
EXPORT_SYMBOL_GPL(hpet_rtc_dropped_irq);

static void hpet_rtc_timer_reinit(void)
{
        unsigned int delta;
        int lost_ints = -1;

        if (unlikely(!hpet_rtc_flags))
                hpet_disable_rtc_channel();

        if (!(hpet_rtc_flags & RTC_PIE) || hpet_pie_limit)
                delta = hpet_default_delta;
        else
                delta = hpet_pie_delta;

        /*
         * Increment the comparator value until we are ahead of the
         * current count.
         */
        do {
                hpet_t1_cmp += delta;
                hpet_writel(hpet_t1_cmp, HPET_T1_CMP);
                lost_ints++;
        } while (!hpet_cnt_ahead(hpet_t1_cmp, hpet_readl(HPET_COUNTER)));

        if (lost_ints) {
                if (hpet_rtc_flags & RTC_PIE)
                        hpet_pie_count += lost_ints;
                if (printk_ratelimit())
                        printk(KERN_WARNING "hpet1: lost %d rtc interrupts\n",
                                lost_ints);
        }
}

irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id)
{
        struct rtc_time curr_time;
        unsigned long rtc_int_flag = 0;

        hpet_rtc_timer_reinit();
        memset(&curr_time, 0, sizeof(struct rtc_time));

        if (hpet_rtc_flags & (RTC_UIE | RTC_AIE))
                get_rtc_time(&curr_time);

        if (hpet_rtc_flags & RTC_UIE &&
            curr_time.tm_sec != hpet_prev_update_sec) {
                if (hpet_prev_update_sec >= 0)
                        rtc_int_flag = RTC_UF;
                hpet_prev_update_sec = curr_time.tm_sec;
        }

        if (hpet_rtc_flags & RTC_PIE &&
            ++hpet_pie_count >= hpet_pie_limit) {
                rtc_int_flag |= RTC_PF;
                hpet_pie_count = 0;
        }

        if (hpet_rtc_flags & RTC_AIE &&
            (curr_time.tm_sec == hpet_alarm_time.tm_sec) &&
            (curr_time.tm_min == hpet_alarm_time.tm_min) &&
            (curr_time.tm_hour == hpet_alarm_time.tm_hour))
                        rtc_int_flag |= RTC_AF;

        if (rtc_int_flag) {
                rtc_int_flag |= (RTC_IRQF | (RTC_NUM_INTS << 8));
                if (irq_handler)
                        irq_handler(rtc_int_flag, dev_id);
        }
        return IRQ_HANDLED;
}
EXPORT_SYMBOL_GPL(hpet_rtc_interrupt);
#endif