WIP FPC-III support

[linux/fpc-iii.git] / drivers / char / hpet.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Intel & MS High Precision Event Timer Implementation.
 *
 * Copyright (C) 2003 Intel Corporation
 *      Venki Pallipadi
 * (c) Copyright 2004 Hewlett-Packard Development Company, L.P.
 *      Bob Picco <robert.picco@hp.com>
 */

#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/miscdevice.h>
#include <linux/major.h>
#include <linux/ioport.h>
#include <linux/fcntl.h>
#include <linux/init.h>
#include <linux/poll.h>
#include <linux/mm.h>
#include <linux/proc_fs.h>
#include <linux/spinlock.h>
#include <linux/sysctl.h>
#include <linux/wait.h>
#include <linux/sched/signal.h>
#include <linux/bcd.h>
#include <linux/seq_file.h>
#include <linux/bitops.h>
#include <linux/compat.h>
#include <linux/clocksource.h>
#include <linux/uaccess.h>
#include <linux/slab.h>
#include <linux/io.h>
#include <linux/acpi.h>
#include <linux/hpet.h>
#include <asm/current.h>
#include <asm/irq.h>
#include <asm/div64.h>

/*
 * The High Precision Event Timer driver.
 * This driver is closely modelled after the rtc.c driver.
 * See HPET spec revision 1.
 */
#define HPET_USER_FREQ  (64)
#define HPET_DRIFT      (500)

#define HPET_RANGE_SIZE         1024    /* from HPET spec */


/* WARNING -- don't get confused.  These macros are never used
 * to write the (single) counter, and rarely to read it.
 * They're badly named; to fix, someday.
 */
#if BITS_PER_LONG == 64
#define write_counter(V, MC)    writeq(V, MC)
#define read_counter(MC)        readq(MC)
#else
#define write_counter(V, MC)    writel(V, MC)
#define read_counter(MC)        readl(MC)
#endif

static DEFINE_MUTEX(hpet_mutex); /* replaces BKL */
static u32 hpet_nhpet, hpet_max_freq = HPET_USER_FREQ;

/* This clocksource driver currently only works on ia64 */
#ifdef CONFIG_IA64
static void __iomem *hpet_mctr;

static u64 read_hpet(struct clocksource *cs)
{
        return (u64)read_counter((void __iomem *)hpet_mctr);
}

static struct clocksource clocksource_hpet = {
        .name           = "hpet",
        .rating         = 250,
        .read           = read_hpet,
        .mask           = CLOCKSOURCE_MASK(64),
        .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
};
static struct clocksource *hpet_clocksource;
#endif

/* A lock for concurrent access by app and isr hpet activity. */
static DEFINE_SPINLOCK(hpet_lock);

#define HPET_DEV_NAME   (7)

struct hpet_dev {
        struct hpets *hd_hpets;
        struct hpet __iomem *hd_hpet;
        struct hpet_timer __iomem *hd_timer;
        unsigned long hd_ireqfreq;
        unsigned long hd_irqdata;
        wait_queue_head_t hd_waitqueue;
        struct fasync_struct *hd_async_queue;
        unsigned int hd_flags;
        unsigned int hd_irq;
        unsigned int hd_hdwirq;
        char hd_name[HPET_DEV_NAME];
};

struct hpets {
        struct hpets *hp_next;
        struct hpet __iomem *hp_hpet;
        unsigned long hp_hpet_phys;
        struct clocksource *hp_clocksource;
        unsigned long long hp_tick_freq;
        unsigned long hp_delta;
        unsigned int hp_ntimer;
        unsigned int hp_which;
        struct hpet_dev hp_dev[];
};

static struct hpets *hpets;

#define HPET_OPEN               0x0001
#define HPET_IE                 0x0002  /* interrupt enabled */
#define HPET_PERIODIC           0x0004
#define HPET_SHARED_IRQ         0x0008


#ifndef readq
static inline unsigned long long readq(void __iomem *addr)
{
        return readl(addr) | (((unsigned long long)readl(addr + 4)) << 32LL);
}
#endif

#ifndef writeq
static inline void writeq(unsigned long long v, void __iomem *addr)
{
        writel(v & 0xffffffff, addr);
        writel(v >> 32, addr + 4);
}
#endif

static irqreturn_t hpet_interrupt(int irq, void *data)
{
        struct hpet_dev *devp;
        unsigned long isr;

        devp = data;
        isr = 1 << (devp - devp->hd_hpets->hp_dev);

        if ((devp->hd_flags & HPET_SHARED_IRQ) &&
            !(isr & readl(&devp->hd_hpet->hpet_isr)))
                return IRQ_NONE;

        spin_lock(&hpet_lock);
        devp->hd_irqdata++;

        /*
         * For non-periodic timers, increment the accumulator.
         * This has the effect of treating non-periodic like periodic.
         */
        if ((devp->hd_flags & (HPET_IE | HPET_PERIODIC)) == HPET_IE) {
                unsigned long m, t, mc, base, k;
                struct hpet __iomem *hpet = devp->hd_hpet;
                struct hpets *hpetp = devp->hd_hpets;

                t = devp->hd_ireqfreq;
                m = read_counter(&devp->hd_timer->hpet_compare);
                mc = read_counter(&hpet->hpet_mc);
                /* The time for the next interrupt would logically be t + m,
                 * however, if we are very unlucky and the interrupt is delayed
                 * for longer than t then we will completely miss the next
                 * interrupt if we set t + m and an application will hang.
                 * Therefore we need to make a more complex computation assuming
                 * that there exists a k for which the following is true:
                 * k * t + base < mc + delta
                 * (k + 1) * t + base > mc + delta
                 * where t is the interval in hpet ticks for the given freq,
                 * base is the theoretical start value 0 < base < t,
                 * mc is the main counter value at the time of the interrupt,
                 * delta is the time it takes to write the a value to the
                 * comparator.
                 * k may then be computed as (mc - base + delta) / t .
                 */
                base = mc % t;
                k = (mc - base + hpetp->hp_delta) / t;
                write_counter(t * (k + 1) + base,
                              &devp->hd_timer->hpet_compare);
        }

        if (devp->hd_flags & HPET_SHARED_IRQ)
                writel(isr, &devp->hd_hpet->hpet_isr);
        spin_unlock(&hpet_lock);

        wake_up_interruptible(&devp->hd_waitqueue);

        kill_fasync(&devp->hd_async_queue, SIGIO, POLL_IN);

        return IRQ_HANDLED;
}

static void hpet_timer_set_irq(struct hpet_dev *devp)
{
        unsigned long v;
        int irq, gsi;
        struct hpet_timer __iomem *timer;

        spin_lock_irq(&hpet_lock);
        if (devp->hd_hdwirq) {
                spin_unlock_irq(&hpet_lock);
                return;
        }

        timer = devp->hd_timer;

        /* we prefer level triggered mode */
        v = readl(&timer->hpet_config);
        if (!(v & Tn_INT_TYPE_CNF_MASK)) {
                v |= Tn_INT_TYPE_CNF_MASK;
                writel(v, &timer->hpet_config);
        }
        spin_unlock_irq(&hpet_lock);

        v = (readq(&timer->hpet_config) & Tn_INT_ROUTE_CAP_MASK) >>
                                 Tn_INT_ROUTE_CAP_SHIFT;

        /*
         * In PIC mode, skip IRQ0-4, IRQ6-9, IRQ12-15 which is always used by
         * legacy device. In IO APIC mode, we skip all the legacy IRQS.
         */
        if (acpi_irq_model == ACPI_IRQ_MODEL_PIC)
                v &= ~0xf3df;
        else
                v &= ~0xffff;

        for_each_set_bit(irq, &v, HPET_MAX_IRQ) {
                if (irq >= nr_irqs) {
                        irq = HPET_MAX_IRQ;
                        break;
                }

                gsi = acpi_register_gsi(NULL, irq, ACPI_LEVEL_SENSITIVE,
                                        ACPI_ACTIVE_LOW);
                if (gsi > 0)
                        break;

                /* FIXME: Setup interrupt source table */
        }

        if (irq < HPET_MAX_IRQ) {
                spin_lock_irq(&hpet_lock);
                v = readl(&timer->hpet_config);
                v |= irq << Tn_INT_ROUTE_CNF_SHIFT;
                writel(v, &timer->hpet_config);
                devp->hd_hdwirq = gsi;
                spin_unlock_irq(&hpet_lock);
        }
        return;
}

static int hpet_open(struct inode *inode, struct file *file)
{
        struct hpet_dev *devp;
        struct hpets *hpetp;
        int i;

        if (file->f_mode & FMODE_WRITE)
                return -EINVAL;

        mutex_lock(&hpet_mutex);
        spin_lock_irq(&hpet_lock);

        for (devp = NULL, hpetp = hpets; hpetp && !devp; hpetp = hpetp->hp_next)
                for (i = 0; i < hpetp->hp_ntimer; i++)
                        if (hpetp->hp_dev[i].hd_flags & HPET_OPEN)
                                continue;
                        else {
                                devp = &hpetp->hp_dev[i];
                                break;
                        }

        if (!devp) {
                spin_unlock_irq(&hpet_lock);
                mutex_unlock(&hpet_mutex);
                return -EBUSY;
        }

        file->private_data = devp;
        devp->hd_irqdata = 0;
        devp->hd_flags |= HPET_OPEN;
        spin_unlock_irq(&hpet_lock);
        mutex_unlock(&hpet_mutex);

        hpet_timer_set_irq(devp);

        return 0;
}

static ssize_t
hpet_read(struct file *file, char __user *buf, size_t count, loff_t * ppos)
{
        DECLARE_WAITQUEUE(wait, current);
        unsigned long data;
        ssize_t retval;
        struct hpet_dev *devp;

        devp = file->private_data;
        if (!devp->hd_ireqfreq)
                return -EIO;

        if (count < sizeof(unsigned long))
                return -EINVAL;

        add_wait_queue(&devp->hd_waitqueue, &wait);

        for ( ; ; ) {
                set_current_state(TASK_INTERRUPTIBLE);

                spin_lock_irq(&hpet_lock);
                data = devp->hd_irqdata;
                devp->hd_irqdata = 0;
                spin_unlock_irq(&hpet_lock);

                if (data)
                        break;
                else if (file->f_flags & O_NONBLOCK) {
                        retval = -EAGAIN;
                        goto out;
                } else if (signal_pending(current)) {
                        retval = -ERESTARTSYS;
                        goto out;
                }
                schedule();
        }

        retval = put_user(data, (unsigned long __user *)buf);
        if (!retval)
                retval = sizeof(unsigned long);
out:
        __set_current_state(TASK_RUNNING);
        remove_wait_queue(&devp->hd_waitqueue, &wait);

        return retval;
}

static __poll_t hpet_poll(struct file *file, poll_table * wait)
{
        unsigned long v;
        struct hpet_dev *devp;

        devp = file->private_data;

        if (!devp->hd_ireqfreq)
                return 0;

        poll_wait(file, &devp->hd_waitqueue, wait);

        spin_lock_irq(&hpet_lock);
        v = devp->hd_irqdata;
        spin_unlock_irq(&hpet_lock);

        if (v != 0)
                return EPOLLIN | EPOLLRDNORM;

        return 0;
}

#ifdef CONFIG_HPET_MMAP
#ifdef CONFIG_HPET_MMAP_DEFAULT
static int hpet_mmap_enabled = 1;
#else
static int hpet_mmap_enabled = 0;
#endif

static __init int hpet_mmap_enable(char *str)
{
        get_option(&str, &hpet_mmap_enabled);
        pr_info("HPET mmap %s\n", hpet_mmap_enabled ? "enabled" : "disabled");
        return 1;
}
__setup("hpet_mmap=", hpet_mmap_enable);

static int hpet_mmap(struct file *file, struct vm_area_struct *vma)
{
        struct hpet_dev *devp;
        unsigned long addr;

        if (!hpet_mmap_enabled)
                return -EACCES;

        devp = file->private_data;
        addr = devp->hd_hpets->hp_hpet_phys;

        if (addr & (PAGE_SIZE - 1))
                return -ENOSYS;

        vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
        return vm_iomap_memory(vma, addr, PAGE_SIZE);
}
#else
static int hpet_mmap(struct file *file, struct vm_area_struct *vma)
{
        return -ENOSYS;
}
#endif

static int hpet_fasync(int fd, struct file *file, int on)
{
        struct hpet_dev *devp;

        devp = file->private_data;

        if (fasync_helper(fd, file, on, &devp->hd_async_queue) >= 0)
                return 0;
        else
                return -EIO;
}

static int hpet_release(struct inode *inode, struct file *file)
{
        struct hpet_dev *devp;
        struct hpet_timer __iomem *timer;
        int irq = 0;

        devp = file->private_data;
        timer = devp->hd_timer;

        spin_lock_irq(&hpet_lock);

        writeq((readq(&timer->hpet_config) & ~Tn_INT_ENB_CNF_MASK),
               &timer->hpet_config);

        irq = devp->hd_irq;
        devp->hd_irq = 0;

        devp->hd_ireqfreq = 0;

        if (devp->hd_flags & HPET_PERIODIC
            && readq(&timer->hpet_config) & Tn_TYPE_CNF_MASK) {
                unsigned long v;

                v = readq(&timer->hpet_config);
                v ^= Tn_TYPE_CNF_MASK;
                writeq(v, &timer->hpet_config);
        }

        devp->hd_flags &= ~(HPET_OPEN | HPET_IE | HPET_PERIODIC);
        spin_unlock_irq(&hpet_lock);

        if (irq)
                free_irq(irq, devp);

        file->private_data = NULL;
        return 0;
}

static int hpet_ioctl_ieon(struct hpet_dev *devp)
{
        struct hpet_timer __iomem *timer;
        struct hpet __iomem *hpet;
        struct hpets *hpetp;
        int irq;
        unsigned long g, v, t, m;
        unsigned long flags, isr;

        timer = devp->hd_timer;
        hpet = devp->hd_hpet;
        hpetp = devp->hd_hpets;

        if (!devp->hd_ireqfreq)
                return -EIO;

        spin_lock_irq(&hpet_lock);

        if (devp->hd_flags & HPET_IE) {
                spin_unlock_irq(&hpet_lock);
                return -EBUSY;
        }

        devp->hd_flags |= HPET_IE;

        if (readl(&timer->hpet_config) & Tn_INT_TYPE_CNF_MASK)
                devp->hd_flags |= HPET_SHARED_IRQ;
        spin_unlock_irq(&hpet_lock);

        irq = devp->hd_hdwirq;

        if (irq) {
                unsigned long irq_flags;

                if (devp->hd_flags & HPET_SHARED_IRQ) {
                        /*
                         * To prevent the interrupt handler from seeing an
                         * unwanted interrupt status bit, program the timer
                         * so that it will not fire in the near future ...
                         */
                        writel(readl(&timer->hpet_config) & ~Tn_TYPE_CNF_MASK,
                               &timer->hpet_config);
                        write_counter(read_counter(&hpet->hpet_mc),
                                      &timer->hpet_compare);
                        /* ... and clear any left-over status. */
                        isr = 1 << (devp - devp->hd_hpets->hp_dev);
                        writel(isr, &hpet->hpet_isr);
                }

                sprintf(devp->hd_name, "hpet%d", (int)(devp - hpetp->hp_dev));
                irq_flags = devp->hd_flags & HPET_SHARED_IRQ ? IRQF_SHARED : 0;
                if (request_irq(irq, hpet_interrupt, irq_flags,
                                devp->hd_name, (void *)devp)) {
                        printk(KERN_ERR "hpet: IRQ %d is not free\n", irq);
                        irq = 0;
                }
        }

        if (irq == 0) {
                spin_lock_irq(&hpet_lock);
                devp->hd_flags ^= HPET_IE;
                spin_unlock_irq(&hpet_lock);
                return -EIO;
        }

        devp->hd_irq = irq;
        t = devp->hd_ireqfreq;
        v = readq(&timer->hpet_config);

        /* 64-bit comparators are not yet supported through the ioctls,
         * so force this into 32-bit mode if it supports both modes
         */
        g = v | Tn_32MODE_CNF_MASK | Tn_INT_ENB_CNF_MASK;

        if (devp->hd_flags & HPET_PERIODIC) {
                g |= Tn_TYPE_CNF_MASK;
                v |= Tn_TYPE_CNF_MASK | Tn_VAL_SET_CNF_MASK;
                writeq(v, &timer->hpet_config);
                local_irq_save(flags);

                /*
                 * NOTE: First we modify the hidden accumulator
                 * register supported by periodic-capable comparators.
                 * We never want to modify the (single) counter; that
                 * would affect all the comparators. The value written
                 * is the counter value when the first interrupt is due.
                 */
                m = read_counter(&hpet->hpet_mc);
                write_counter(t + m + hpetp->hp_delta, &timer->hpet_compare);
                /*
                 * Then we modify the comparator, indicating the period
                 * for subsequent interrupt.
                 */
                write_counter(t, &timer->hpet_compare);
        } else {
                local_irq_save(flags);
                m = read_counter(&hpet->hpet_mc);
                write_counter(t + m + hpetp->hp_delta, &timer->hpet_compare);
        }

        if (devp->hd_flags & HPET_SHARED_IRQ) {
                isr = 1 << (devp - devp->hd_hpets->hp_dev);
                writel(isr, &hpet->hpet_isr);
        }
        writeq(g, &timer->hpet_config);
        local_irq_restore(flags);

        return 0;
}

/* converts Hz to number of timer ticks */
static inline unsigned long hpet_time_div(struct hpets *hpets,
                                          unsigned long dis)
{
        unsigned long long m;

        m = hpets->hp_tick_freq + (dis >> 1);
        return div64_ul(m, dis);
}

static int
hpet_ioctl_common(struct hpet_dev *devp, unsigned int cmd, unsigned long arg,
                  struct hpet_info *info)
{
        struct hpet_timer __iomem *timer;
        struct hpets *hpetp;
        int err;
        unsigned long v;

        switch (cmd) {
        case HPET_IE_OFF:
        case HPET_INFO:
        case HPET_EPI:
        case HPET_DPI:
        case HPET_IRQFREQ:
                timer = devp->hd_timer;
                hpetp = devp->hd_hpets;
                break;
        case HPET_IE_ON:
                return hpet_ioctl_ieon(devp);
        default:
                return -EINVAL;
        }

        err = 0;

        switch (cmd) {
        case HPET_IE_OFF:
                if ((devp->hd_flags & HPET_IE) == 0)
                        break;
                v = readq(&timer->hpet_config);
                v &= ~Tn_INT_ENB_CNF_MASK;
                writeq(v, &timer->hpet_config);
                if (devp->hd_irq) {
                        free_irq(devp->hd_irq, devp);
                        devp->hd_irq = 0;
                }
                devp->hd_flags ^= HPET_IE;
                break;
        case HPET_INFO:
                {
                        memset(info, 0, sizeof(*info));
                        if (devp->hd_ireqfreq)
                                info->hi_ireqfreq =
                                        hpet_time_div(hpetp, devp->hd_ireqfreq);
                        info->hi_flags =
                            readq(&timer->hpet_config) & Tn_PER_INT_CAP_MASK;
                        info->hi_hpet = hpetp->hp_which;
                        info->hi_timer = devp - hpetp->hp_dev;
                        break;
                }
        case HPET_EPI:
                v = readq(&timer->hpet_config);
                if ((v & Tn_PER_INT_CAP_MASK) == 0) {
                        err = -ENXIO;
                        break;
                }
                devp->hd_flags |= HPET_PERIODIC;
                break;
        case HPET_DPI:
                v = readq(&timer->hpet_config);
                if ((v & Tn_PER_INT_CAP_MASK) == 0) {
                        err = -ENXIO;
                        break;
                }
                if (devp->hd_flags & HPET_PERIODIC &&
                    readq(&timer->hpet_config) & Tn_TYPE_CNF_MASK) {
                        v = readq(&timer->hpet_config);
                        v ^= Tn_TYPE_CNF_MASK;
                        writeq(v, &timer->hpet_config);
                }
                devp->hd_flags &= ~HPET_PERIODIC;
                break;
        case HPET_IRQFREQ:
                if ((arg > hpet_max_freq) &&
                    !capable(CAP_SYS_RESOURCE)) {
                        err = -EACCES;
                        break;
                }

                if (!arg) {
                        err = -EINVAL;
                        break;
                }

                devp->hd_ireqfreq = hpet_time_div(hpetp, arg);
        }

        return err;
}

static long
hpet_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
        struct hpet_info info;
        int err;

        mutex_lock(&hpet_mutex);
        err = hpet_ioctl_common(file->private_data, cmd, arg, &info);
        mutex_unlock(&hpet_mutex);

        if ((cmd == HPET_INFO) && !err &&
            (copy_to_user((void __user *)arg, &info, sizeof(info))))
                err = -EFAULT;

        return err;
}

#ifdef CONFIG_COMPAT
struct compat_hpet_info {
        compat_ulong_t hi_ireqfreq;     /* Hz */
        compat_ulong_t hi_flags;        /* information */
        unsigned short hi_hpet;
        unsigned short hi_timer;
};

static long
hpet_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
        struct hpet_info info;
        int err;

        mutex_lock(&hpet_mutex);
        err = hpet_ioctl_common(file->private_data, cmd, arg, &info);
        mutex_unlock(&hpet_mutex);

        if ((cmd == HPET_INFO) && !err) {
                struct compat_hpet_info __user *u = compat_ptr(arg);
                if (put_user(info.hi_ireqfreq, &u->hi_ireqfreq) ||
                    put_user(info.hi_flags, &u->hi_flags) ||
                    put_user(info.hi_hpet, &u->hi_hpet) ||
                    put_user(info.hi_timer, &u->hi_timer))
                        err = -EFAULT;
        }

        return err;
}
#endif

static const struct file_operations hpet_fops = {
        .owner = THIS_MODULE,
        .llseek = no_llseek,
        .read = hpet_read,
        .poll = hpet_poll,
        .unlocked_ioctl = hpet_ioctl,
#ifdef CONFIG_COMPAT
        .compat_ioctl = hpet_compat_ioctl,
#endif
        .open = hpet_open,
        .release = hpet_release,
        .fasync = hpet_fasync,
        .mmap = hpet_mmap,
};

static int hpet_is_known(struct hpet_data *hdp)
{
        struct hpets *hpetp;

        for (hpetp = hpets; hpetp; hpetp = hpetp->hp_next)
                if (hpetp->hp_hpet_phys == hdp->hd_phys_address)
                        return 1;

        return 0;
}

static struct ctl_table hpet_table[] = {
        {
         .procname = "max-user-freq",
         .data = &hpet_max_freq,
         .maxlen = sizeof(int),
         .mode = 0644,
         .proc_handler = proc_dointvec,
         },
        {}
};

static struct ctl_table hpet_root[] = {
        {
         .procname = "hpet",
         .maxlen = 0,
         .mode = 0555,
         .child = hpet_table,
         },
        {}
};

static struct ctl_table dev_root[] = {
        {
         .procname = "dev",
         .maxlen = 0,
         .mode = 0555,
         .child = hpet_root,
         },
        {}
};

static struct ctl_table_header *sysctl_header;

/*
 * Adjustment for when arming the timer with
 * initial conditions.  That is, main counter
 * ticks expired before interrupts are enabled.
 */
#define TICK_CALIBRATE  (1000UL)

static unsigned long __hpet_calibrate(struct hpets *hpetp)
{
        struct hpet_timer __iomem *timer = NULL;
        unsigned long t, m, count, i, flags, start;
        struct hpet_dev *devp;
        int j;
        struct hpet __iomem *hpet;

        for (j = 0, devp = hpetp->hp_dev; j < hpetp->hp_ntimer; j++, devp++)
                if ((devp->hd_flags & HPET_OPEN) == 0) {
                        timer = devp->hd_timer;
                        break;
                }

        if (!timer)
                return 0;

        hpet = hpetp->hp_hpet;
        t = read_counter(&timer->hpet_compare);

        i = 0;
        count = hpet_time_div(hpetp, TICK_CALIBRATE);

        local_irq_save(flags);

        start = read_counter(&hpet->hpet_mc);

        do {
                m = read_counter(&hpet->hpet_mc);
                write_counter(t + m + hpetp->hp_delta, &timer->hpet_compare);
        } while (i++, (m - start) < count);

        local_irq_restore(flags);

        return (m - start) / i;
}

static unsigned long hpet_calibrate(struct hpets *hpetp)
{
        unsigned long ret = ~0UL;
        unsigned long tmp;

        /*
         * Try to calibrate until return value becomes stable small value.
         * If SMI interruption occurs in calibration loop, the return value
         * will be big. This avoids its impact.
         */
        for ( ; ; ) {
                tmp = __hpet_calibrate(hpetp);
                if (ret <= tmp)
                        break;
                ret = tmp;
        }

        return ret;
}

int hpet_alloc(struct hpet_data *hdp)
{
        u64 cap, mcfg;
        struct hpet_dev *devp;
        u32 i, ntimer;
        struct hpets *hpetp;
        struct hpet __iomem *hpet;
        static struct hpets *last;
        unsigned long period;
        unsigned long long temp;
        u32 remainder;

        /*
         * hpet_alloc can be called by platform dependent code.
         * If platform dependent code has allocated the hpet that
         * ACPI has also reported, then we catch it here.
         */
        if (hpet_is_known(hdp)) {
                printk(KERN_DEBUG "%s: duplicate HPET ignored\n",
                        __func__);
                return 0;
        }

        hpetp = kzalloc(struct_size(hpetp, hp_dev, hdp->hd_nirqs),
                        GFP_KERNEL);

        if (!hpetp)
                return -ENOMEM;

        hpetp->hp_which = hpet_nhpet++;
        hpetp->hp_hpet = hdp->hd_address;
        hpetp->hp_hpet_phys = hdp->hd_phys_address;

        hpetp->hp_ntimer = hdp->hd_nirqs;

        for (i = 0; i < hdp->hd_nirqs; i++)
                hpetp->hp_dev[i].hd_hdwirq = hdp->hd_irq[i];

        hpet = hpetp->hp_hpet;

        cap = readq(&hpet->hpet_cap);

        ntimer = ((cap & HPET_NUM_TIM_CAP_MASK) >> HPET_NUM_TIM_CAP_SHIFT) + 1;

        if (hpetp->hp_ntimer != ntimer) {
                printk(KERN_WARNING "hpet: number irqs doesn't agree"
                       " with number of timers\n");
                kfree(hpetp);
                return -ENODEV;
        }

        if (last)
                last->hp_next = hpetp;
        else
                hpets = hpetp;

        last = hpetp;

        period = (cap & HPET_COUNTER_CLK_PERIOD_MASK) >>
                HPET_COUNTER_CLK_PERIOD_SHIFT; /* fs, 10^-15 */
        temp = 1000000000000000uLL; /* 10^15 femtoseconds per second */
        temp += period >> 1; /* round */
        do_div(temp, period);
        hpetp->hp_tick_freq = temp; /* ticks per second */

        printk(KERN_INFO "hpet%d: at MMIO 0x%lx, IRQ%s",
                hpetp->hp_which, hdp->hd_phys_address,
                hpetp->hp_ntimer > 1 ? "s" : "");
        for (i = 0; i < hpetp->hp_ntimer; i++)
                printk(KERN_CONT "%s %d", i > 0 ? "," : "", hdp->hd_irq[i]);
        printk(KERN_CONT "\n");

        temp = hpetp->hp_tick_freq;
        remainder = do_div(temp, 1000000);
        printk(KERN_INFO
                "hpet%u: %u comparators, %d-bit %u.%06u MHz counter\n",
                hpetp->hp_which, hpetp->hp_ntimer,
                cap & HPET_COUNTER_SIZE_MASK ? 64 : 32,
                (unsigned) temp, remainder);

        mcfg = readq(&hpet->hpet_config);
        if ((mcfg & HPET_ENABLE_CNF_MASK) == 0) {
                write_counter(0L, &hpet->hpet_mc);
                mcfg |= HPET_ENABLE_CNF_MASK;
                writeq(mcfg, &hpet->hpet_config);
        }

        for (i = 0, devp = hpetp->hp_dev; i < hpetp->hp_ntimer; i++, devp++) {
                struct hpet_timer __iomem *timer;

                timer = &hpet->hpet_timers[devp - hpetp->hp_dev];

                devp->hd_hpets = hpetp;
                devp->hd_hpet = hpet;
                devp->hd_timer = timer;

                /*
                 * If the timer was reserved by platform code,
                 * then make timer unavailable for opens.
                 */
                if (hdp->hd_state & (1 << i)) {
                        devp->hd_flags = HPET_OPEN;
                        continue;
                }

                init_waitqueue_head(&devp->hd_waitqueue);
        }

        hpetp->hp_delta = hpet_calibrate(hpetp);

/* This clocksource driver currently only works on ia64 */
#ifdef CONFIG_IA64
        if (!hpet_clocksource) {
                hpet_mctr = (void __iomem *)&hpetp->hp_hpet->hpet_mc;
                clocksource_hpet.archdata.fsys_mmio = hpet_mctr;
                clocksource_register_hz(&clocksource_hpet, hpetp->hp_tick_freq);
                hpetp->hp_clocksource = &clocksource_hpet;
                hpet_clocksource = &clocksource_hpet;
        }
#endif

        return 0;
}

static acpi_status hpet_resources(struct acpi_resource *res, void *data)
{
        struct hpet_data *hdp;
        acpi_status status;
        struct acpi_resource_address64 addr;

        hdp = data;

        status = acpi_resource_to_address64(res, &addr);

        if (ACPI_SUCCESS(status)) {
                hdp->hd_phys_address = addr.address.minimum;
                hdp->hd_address = ioremap(addr.address.minimum, addr.address.address_length);
                if (!hdp->hd_address)
                        return AE_ERROR;

                if (hpet_is_known(hdp)) {
                        iounmap(hdp->hd_address);
                        return AE_ALREADY_EXISTS;
                }
        } else if (res->type == ACPI_RESOURCE_TYPE_FIXED_MEMORY32) {
                struct acpi_resource_fixed_memory32 *fixmem32;

                fixmem32 = &res->data.fixed_memory32;

                hdp->hd_phys_address = fixmem32->address;
                hdp->hd_address = ioremap(fixmem32->address,
                                                HPET_RANGE_SIZE);

                if (hpet_is_known(hdp)) {
                        iounmap(hdp->hd_address);
                        return AE_ALREADY_EXISTS;
                }
        } else if (res->type == ACPI_RESOURCE_TYPE_EXTENDED_IRQ) {
                struct acpi_resource_extended_irq *irqp;
                int i, irq;

                irqp = &res->data.extended_irq;

                for (i = 0; i < irqp->interrupt_count; i++) {
                        if (hdp->hd_nirqs >= HPET_MAX_TIMERS)
                                break;

                        irq = acpi_register_gsi(NULL, irqp->interrupts[i],
                                      irqp->triggering, irqp->polarity);
                        if (irq < 0)
                                return AE_ERROR;

                        hdp->hd_irq[hdp->hd_nirqs] = irq;
                        hdp->hd_nirqs++;
                }
        }

        return AE_OK;
}

static int hpet_acpi_add(struct acpi_device *device)
{
        acpi_status result;
        struct hpet_data data;

        memset(&data, 0, sizeof(data));

        result =
            acpi_walk_resources(device->handle, METHOD_NAME__CRS,
                                hpet_resources, &data);

        if (ACPI_FAILURE(result))
                return -ENODEV;

        if (!data.hd_address || !data.hd_nirqs) {
                if (data.hd_address)
                        iounmap(data.hd_address);
                printk("%s: no address or irqs in _CRS\n", __func__);
                return -ENODEV;
        }

        return hpet_alloc(&data);
}

static const struct acpi_device_id hpet_device_ids[] = {
        {"PNP0103", 0},
        {"", 0},
};

static struct acpi_driver hpet_acpi_driver = {
        .name = "hpet",
        .ids = hpet_device_ids,
        .ops = {
                .add = hpet_acpi_add,
                },
};

static struct miscdevice hpet_misc = { HPET_MINOR, "hpet", &hpet_fops };

static int __init hpet_init(void)
{
        int result;

        result = misc_register(&hpet_misc);
        if (result < 0)
                return -ENODEV;

        sysctl_header = register_sysctl_table(dev_root);

        result = acpi_bus_register_driver(&hpet_acpi_driver);
        if (result < 0) {
                if (sysctl_header)
                        unregister_sysctl_table(sysctl_header);
                misc_deregister(&hpet_misc);
                return result;
        }

        return 0;
}
device_initcall(hpet_init);

/*
MODULE_AUTHOR("Bob Picco <Robert.Picco@hp.com>");
MODULE_LICENSE("GPL");
*/