/*
 * linux/kernel/time/clocksource.c
 *
 * This file contains the functions which manage clocksource drivers.
 *
 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 * TODO WishList:
 *   o Allow clocksource drivers to be unregistered
 *   o get rid of clocksource_jiffies extern
 */

#include <linux/clocksource.h>
#include <linux/sysdev.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
#include <linux/tick.h>

/* XXX - Would like a better way for initializing curr_clocksource */
extern struct clocksource clocksource_jiffies;

/*[Clocksource internal variables]---------
 * curr_clocksource:
 *      currently selected clocksource. Initialized to clocksource_jiffies.
 * next_clocksource:
 *      pending next selected clocksource.
 * clocksource_list:
 *      linked list with the registered clocksources
 * clocksource_lock:
 *      protects manipulations to curr_clocksource and next_clocksource
 *      and the clocksource_list
 * override_name:
 *      Name of the user-specified clocksource.
 */
static struct clocksource *curr_clocksource = &clocksource_jiffies;
static struct clocksource *next_clocksource;
static struct clocksource *clocksource_override;
static LIST_HEAD(clocksource_list);
static DEFINE_SPINLOCK(clocksource_lock);
static char override_name[32];
static int finished_booting;

/* clocksource_done_booting - Called near the end of core bootup
 *
 * Hack to avoid lots of clocksource churn at boot time.
 * We use fs_initcall because we want this to start before
 * device_initcall but after subsys_initcall.
 */
static int __init clocksource_done_booting(void)
{
        finished_booting = 1;
        return 0;
}
fs_initcall(clocksource_done_booting);

#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
static LIST_HEAD(watchdog_list);
static struct clocksource *watchdog;
static struct timer_list watchdog_timer;
static DEFINE_SPINLOCK(watchdog_lock);
static cycle_t watchdog_last;
static unsigned long watchdog_resumed;

/*
 * Interval: 0.5sec Threshold: 0.0625s
 */
#define WATCHDOG_INTERVAL (HZ >> 1)
#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)

static void clocksource_ratewd(struct clocksource *cs, int64_t delta)
{
        if (delta > -WATCHDOG_THRESHOLD && delta < WATCHDOG_THRESHOLD)
                return;

        printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
               cs->name, delta);
        cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
        clocksource_change_rating(cs, 0);
        list_del(&cs->wd_list);
}

static void clocksource_watchdog(unsigned long data)
{
        struct clocksource *cs, *tmp;
        cycle_t csnow, wdnow;
        int64_t wd_nsec, cs_nsec;
        int resumed;

        spin_lock(&watchdog_lock);

        resumed = test_and_clear_bit(0, &watchdog_resumed);

        wdnow = watchdog->read();
        wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
        watchdog_last = wdnow;

        list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
                csnow = cs->read();

                if (unlikely(resumed)) {
                        cs->wd_last = csnow;
                        continue;
                }

                /* Initialized ? */
                if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
                        if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
                            (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
                                cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
                                /*
                                 * We just marked the clocksource as
                                 * highres-capable, notify the rest of the
                                 * system as well so that we transition
                                 * into high-res mode:
                                 */
                                tick_clock_notify();
                        }
                        cs->flags |= CLOCK_SOURCE_WATCHDOG;
                        cs->wd_last = csnow;
                } else {
                        cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
                        cs->wd_last = csnow;
                        /* Check the delta. Might remove from the list ! */
                        clocksource_ratewd(cs, cs_nsec - wd_nsec);
                }
        }

        if (!list_empty(&watchdog_list)) {
                /*
                 * Cycle through CPUs to check if the CPUs stay
                 * synchronized to each other.
                 */
                int next_cpu = cpumask_next(raw_smp_processor_id(),
                                            cpu_online_mask);

                if (next_cpu >= nr_cpu_ids)
                        next_cpu = cpumask_first(cpu_online_mask);
                watchdog_timer.expires += WATCHDOG_INTERVAL;
                add_timer_on(&watchdog_timer, next_cpu);
        }
        spin_unlock(&watchdog_lock);
}
static void clocksource_resume_watchdog(void)
{
        set_bit(0, &watchdog_resumed);
}

static void clocksource_check_watchdog(struct clocksource *cs)
{
        struct clocksource *cse;
        unsigned long flags;

        spin_lock_irqsave(&watchdog_lock, flags);
        if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
                int started = !list_empty(&watchdog_list);

                list_add(&cs->wd_list, &watchdog_list);
                if (!started && watchdog) {
                        watchdog_last = watchdog->read();
                        watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
                        add_timer_on(&watchdog_timer,
                                     cpumask_first(cpu_online_mask));
                }
        } else {
                if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
                        cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;

                if (!watchdog || cs->rating > watchdog->rating) {
                        if (watchdog)
                                del_timer(&watchdog_timer);
                        watchdog = cs;
                        init_timer(&watchdog_timer);
                        watchdog_timer.function = clocksource_watchdog;

                        /* Reset watchdog cycles */
                        list_for_each_entry(cse, &watchdog_list, wd_list)
                                cse->flags &= ~CLOCK_SOURCE_WATCHDOG;
                        /* Start if list is not empty */
                        if (!list_empty(&watchdog_list)) {
                                watchdog_last = watchdog->read();
                                watchdog_timer.expires =
                                        jiffies + WATCHDOG_INTERVAL;
                                add_timer_on(&watchdog_timer,
                                             cpumask_first(cpu_online_mask));
                        }
                }
        }
        spin_unlock_irqrestore(&watchdog_lock, flags);
}
#else
static void clocksource_check_watchdog(struct clocksource *cs)
{
        if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
                cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
}

static inline void clocksource_resume_watchdog(void) { }
#endif

/**
 * clocksource_resume - resume the clocksource(s)
 */
void clocksource_resume(void)
{
        struct clocksource *cs;
        unsigned long flags;

        spin_lock_irqsave(&clocksource_lock, flags);

        list_for_each_entry(cs, &clocksource_list, list) {
                if (cs->resume)
                        cs->resume();
        }

        clocksource_resume_watchdog();

        spin_unlock_irqrestore(&clocksource_lock, flags);
}

/**
 * clocksource_touch_watchdog - Update watchdog
 *
 * Update the watchdog after exception contexts such as kgdb so as not
 * to incorrectly trip the watchdog.
 *
 */
void clocksource_touch_watchdog(void)
{
        clocksource_resume_watchdog();
}

/**
 * clocksource_get_next - Returns the selected clocksource
 *
 */
struct clocksource *clocksource_get_next(void)
{
        unsigned long flags;

        spin_lock_irqsave(&clocksource_lock, flags);
        if (next_clocksource && finished_booting) {
                curr_clocksource = next_clocksource;
                next_clocksource = NULL;
        }
        spin_unlock_irqrestore(&clocksource_lock, flags);

        return curr_clocksource;
}

/**
 * select_clocksource - Selects the best registered clocksource.
 *
 * Private function. Must hold clocksource_lock when called.
 *
 * Select the clocksource with the best rating, or the clocksource,
 * which is selected by userspace override.
 */
static struct clocksource *select_clocksource(void)
{
        struct clocksource *next;

        if (list_empty(&clocksource_list))
                return NULL;

        if (clocksource_override)
                next = clocksource_override;
        else
                next = list_entry(clocksource_list.next, struct clocksource,
                                  list);

        if (next == curr_clocksource)
                return NULL;

        return next;
}

/*
 * Enqueue the clocksource sorted by rating
 */
static int clocksource_enqueue(struct clocksource *c)
{
        struct list_head *tmp, *entry = &clocksource_list;

        list_for_each(tmp, &clocksource_list) {
                struct clocksource *cs;

                cs = list_entry(tmp, struct clocksource, list);
                if (cs == c)
                        return -EBUSY;
                /* Keep track of the place, where to insert */
                if (cs->rating >= c->rating)
                        entry = tmp;
        }
        list_add(&c->list, entry);

        if (strlen(c->name) == strlen(override_name) &&
            !strcmp(c->name, override_name))
                clocksource_override = c;

        return 0;
}

/**
 * clocksource_register - Used to install new clocksources
 * @t:          clocksource to be registered
 *
 * Returns -EBUSY if registration fails, zero otherwise.
 */
int clocksource_register(struct clocksource *c)
{
        unsigned long flags;
        int ret;

        /* save mult_orig on registration */
        c->mult_orig = c->mult;

        spin_lock_irqsave(&clocksource_lock, flags);
        ret = clocksource_enqueue(c);
        if (!ret)
                next_clocksource = select_clocksource();
        spin_unlock_irqrestore(&clocksource_lock, flags);
        if (!ret)
                clocksource_check_watchdog(c);
        return ret;
}
EXPORT_SYMBOL(clocksource_register);

/**
 * clocksource_change_rating - Change the rating of a registered clocksource
 *
 */
void clocksource_change_rating(struct clocksource *cs, int rating)
{
        unsigned long flags;

        spin_lock_irqsave(&clocksource_lock, flags);
        list_del(&cs->list);
        cs->rating = rating;
        clocksource_enqueue(cs);
        next_clocksource = select_clocksource();
        spin_unlock_irqrestore(&clocksource_lock, flags);
}

/**
 * clocksource_unregister - remove a registered clocksource
 */
void clocksource_unregister(struct clocksource *cs)
{
        unsigned long flags;

        spin_lock_irqsave(&clocksource_lock, flags);
        list_del(&cs->list);
        if (clocksource_override == cs)
                clocksource_override = NULL;
        next_clocksource = select_clocksource();
        spin_unlock_irqrestore(&clocksource_lock, flags);
}

#ifdef CONFIG_SYSFS
/**
 * sysfs_show_current_clocksources - sysfs interface for current clocksource
 * @dev:        unused
 * @buf:        char buffer to be filled with clocksource list
 *
 * Provides sysfs interface for listing current clocksource.
 */
static ssize_t
sysfs_show_current_clocksources(struct sys_device *dev,
                                struct sysdev_attribute *attr, char *buf)
{
        ssize_t count = 0;

        spin_lock_irq(&clocksource_lock);
        count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
        spin_unlock_irq(&clocksource_lock);

        return count;
}

/**
 * sysfs_override_clocksource - interface for manually overriding clocksource
 * @dev:        unused
 * @buf:        name of override clocksource
 * @count:      length of buffer
 *
 * Takes input from sysfs interface for manually overriding the default
 * clocksource selction.
 */
static ssize_t sysfs_override_clocksource(struct sys_device *dev,
                                          struct sysdev_attribute *attr,
                                          const char *buf, size_t count)
{
        struct clocksource *ovr = NULL;
        size_t ret = count;
        int len;

        /* strings from sysfs write are not 0 terminated! */
        if (count >= sizeof(override_name))
                return -EINVAL;

        /* strip of \n: */
        if (buf[count-1] == '\n')
                count--;

        spin_lock_irq(&clocksource_lock);

        if (count > 0)
                memcpy(override_name, buf, count);
        override_name[count] = 0;

        len = strlen(override_name);
        if (len) {
                struct clocksource *cs;

                ovr = clocksource_override;
                /* try to select it: */
                list_for_each_entry(cs, &clocksource_list, list) {
                        if (strlen(cs->name) == len &&
                            !strcmp(cs->name, override_name))
                                ovr = cs;
                }
        }

        /* Reselect, when the override name has changed */
        if (ovr != clocksource_override) {
                clocksource_override = ovr;
                next_clocksource = select_clocksource();
        }

        spin_unlock_irq(&clocksource_lock);

        return ret;
}

/**
 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
 * @dev:        unused
 * @buf:        char buffer to be filled with clocksource list
 *
 * Provides sysfs interface for listing registered clocksources
 */
static ssize_t
sysfs_show_available_clocksources(struct sys_device *dev,
                                  struct sysdev_attribute *attr,
                                  char *buf)
{
        struct clocksource *src;
        ssize_t count = 0;

        spin_lock_irq(&clocksource_lock);
        list_for_each_entry(src, &clocksource_list, list) {
                count += snprintf(buf + count,
                                  max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
                                  "%s ", src->name);
        }
        spin_unlock_irq(&clocksource_lock);

        count += snprintf(buf + count,
                          max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");

        return count;
}

/*
 * Sysfs setup bits:
 */
static SYSDEV_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
                   sysfs_override_clocksource);

static SYSDEV_ATTR(available_clocksource, 0444,
                   sysfs_show_available_clocksources, NULL);

static struct sysdev_class clocksource_sysclass = {
        .name = "clocksource",
};

static struct sys_device device_clocksource = {
        .id     = 0,
        .cls    = &clocksource_sysclass,
};

static int __init init_clocksource_sysfs(void)
{
        int error = sysdev_class_register(&clocksource_sysclass);

        if (!error)
                error = sysdev_register(&device_clocksource);
        if (!error)
                error = sysdev_create_file(
                                &device_clocksource,
                                &attr_current_clocksource);
        if (!error)
                error = sysdev_create_file(
                                &device_clocksource,
                                &attr_available_clocksource);
        return error;
}

device_initcall(init_clocksource_sysfs);
#endif /* CONFIG_SYSFS */

/**
 * boot_override_clocksource - boot clock override
 * @str:        override name
 *
 * Takes a clocksource= boot argument and uses it
 * as the clocksource override name.
 */
static int __init boot_override_clocksource(char* str)
{
        unsigned long flags;
        spin_lock_irqsave(&clocksource_lock, flags);
        if (str)
                strlcpy(override_name, str, sizeof(override_name));
        spin_unlock_irqrestore(&clocksource_lock, flags);
        return 1;
}

__setup("clocksource=", boot_override_clocksource);

/**
 * boot_override_clock - Compatibility layer for deprecated boot option
 * @str:        override name
 *
 * DEPRECATED! Takes a clock= boot argument and uses it
 * as the clocksource override name
 */
static int __init boot_override_clock(char* str)
{
        if (!strcmp(str, "pmtmr")) {
                printk("Warning: clock=pmtmr is deprecated. "
                        "Use clocksource=acpi_pm.\n");
                return boot_override_clocksource("acpi_pm");
        }
        printk("Warning! clock= boot option is deprecated. "
                "Use clocksource=xyz\n");
        return boot_override_clocksource(str);
}

__setup("clock=", boot_override_clock);