Merge branch 'tracing-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

[linux-2.6] / arch / powerpc / kernel / time.c

/*
 * Common time routines among all ppc machines.
 *
 * Written by Cort Dougan (cort@cs.nmt.edu) to merge
 * Paul Mackerras' version and mine for PReP and Pmac.
 * MPC8xx/MBX changes by Dan Malek (dmalek@jlc.net).
 * Converted for 64-bit by Mike Corrigan (mikejc@us.ibm.com)
 *
 * First round of bugfixes by Gabriel Paubert (paubert@iram.es)
 * to make clock more stable (2.4.0-test5). The only thing
 * that this code assumes is that the timebases have been synchronized
 * by firmware on SMP and are never stopped (never do sleep
 * on SMP then, nap and doze are OK).
 * 
 * Speeded up do_gettimeofday by getting rid of references to
 * xtime (which required locks for consistency). (mikejc@us.ibm.com)
 *
 * TODO (not necessarily in this file):
 * - improve precision and reproducibility of timebase frequency
 * measurement at boot time. (for iSeries, we calibrate the timebase
 * against the Titan chip's clock.)
 * - for astronomical applications: add a new function to get
 * non ambiguous timestamps even around leap seconds. This needs
 * a new timestamp format and a good name.
 *
 * 1997-09-10  Updated NTP code according to technical memorandum Jan '96
 *             "A Kernel Model for Precision Timekeeping" by Dave Mills
 *
 *      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.
 */

#include <linux/errno.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/param.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/timex.h>
#include <linux/kernel_stat.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/profile.h>
#include <linux/cpu.h>
#include <linux/security.h>
#include <linux/percpu.h>
#include <linux/rtc.h>
#include <linux/jiffies.h>
#include <linux/posix-timers.h>
#include <linux/irq.h>

#include <asm/io.h>
#include <asm/processor.h>
#include <asm/nvram.h>
#include <asm/cache.h>
#include <asm/machdep.h>
#include <asm/uaccess.h>
#include <asm/time.h>
#include <asm/prom.h>
#include <asm/irq.h>
#include <asm/div64.h>
#include <asm/smp.h>
#include <asm/vdso_datapage.h>
#include <asm/firmware.h>
#include <asm/cputime.h>
#ifdef CONFIG_PPC_ISERIES
#include <asm/iseries/it_lp_queue.h>
#include <asm/iseries/hv_call_xm.h>
#endif

/* powerpc clocksource/clockevent code */

#include <linux/clockchips.h>
#include <linux/clocksource.h>

static cycle_t rtc_read(void);
static struct clocksource clocksource_rtc = {
        .name         = "rtc",
        .rating       = 400,
        .flags        = CLOCK_SOURCE_IS_CONTINUOUS,
        .mask         = CLOCKSOURCE_MASK(64),
        .shift        = 22,
        .mult         = 0,      /* To be filled in */
        .read         = rtc_read,
};

static cycle_t timebase_read(void);
static struct clocksource clocksource_timebase = {
        .name         = "timebase",
        .rating       = 400,
        .flags        = CLOCK_SOURCE_IS_CONTINUOUS,
        .mask         = CLOCKSOURCE_MASK(64),
        .shift        = 22,
        .mult         = 0,      /* To be filled in */
        .read         = timebase_read,
};

#define DECREMENTER_MAX 0x7fffffff

static int decrementer_set_next_event(unsigned long evt,
                                      struct clock_event_device *dev);
static void decrementer_set_mode(enum clock_event_mode mode,
                                 struct clock_event_device *dev);

static struct clock_event_device decrementer_clockevent = {
       .name           = "decrementer",
       .rating         = 200,
       .shift          = 16,
       .mult           = 0,     /* To be filled in */
       .irq            = 0,
       .set_next_event = decrementer_set_next_event,
       .set_mode       = decrementer_set_mode,
       .features       = CLOCK_EVT_FEAT_ONESHOT,
};

struct decrementer_clock {
        struct clock_event_device event;
        u64 next_tb;
};

static DEFINE_PER_CPU(struct decrementer_clock, decrementers);

#ifdef CONFIG_PPC_ISERIES
static unsigned long __initdata iSeries_recal_titan;
static signed long __initdata iSeries_recal_tb;

/* Forward declaration is only needed for iSereis compiles */
static void __init clocksource_init(void);
#endif

#define XSEC_PER_SEC (1024*1024)

#ifdef CONFIG_PPC64
#define SCALE_XSEC(xsec, max)   (((xsec) * max) / XSEC_PER_SEC)
#else
/* compute ((xsec << 12) * max) >> 32 */
#define SCALE_XSEC(xsec, max)   mulhwu((xsec) << 12, max)
#endif

unsigned long tb_ticks_per_jiffy;
unsigned long tb_ticks_per_usec = 100; /* sane default */
EXPORT_SYMBOL(tb_ticks_per_usec);
unsigned long tb_ticks_per_sec;
EXPORT_SYMBOL(tb_ticks_per_sec);        /* for cputime_t conversions */
u64 tb_to_xs;
unsigned tb_to_us;

#define TICKLEN_SCALE   NTP_SCALE_SHIFT
static u64 last_tick_len;       /* units are ns / 2^TICKLEN_SCALE */
static u64 ticklen_to_xs;       /* 0.64 fraction */

/* If last_tick_len corresponds to about 1/HZ seconds, then
   last_tick_len << TICKLEN_SHIFT will be about 2^63. */
#define TICKLEN_SHIFT   (63 - 30 - TICKLEN_SCALE + SHIFT_HZ)

DEFINE_SPINLOCK(rtc_lock);
EXPORT_SYMBOL_GPL(rtc_lock);

static u64 tb_to_ns_scale __read_mostly;
static unsigned tb_to_ns_shift __read_mostly;
static unsigned long boot_tb __read_mostly;

extern struct timezone sys_tz;
static long timezone_offset;

unsigned long ppc_proc_freq;
EXPORT_SYMBOL(ppc_proc_freq);
unsigned long ppc_tb_freq;

static u64 tb_last_jiffy __cacheline_aligned_in_smp;
static DEFINE_PER_CPU(u64, last_jiffy);

#ifdef CONFIG_VIRT_CPU_ACCOUNTING
/*
 * Factors for converting from cputime_t (timebase ticks) to
 * jiffies, milliseconds, seconds, and clock_t (1/USER_HZ seconds).
 * These are all stored as 0.64 fixed-point binary fractions.
 */
u64 __cputime_jiffies_factor;
EXPORT_SYMBOL(__cputime_jiffies_factor);
u64 __cputime_msec_factor;
EXPORT_SYMBOL(__cputime_msec_factor);
u64 __cputime_sec_factor;
EXPORT_SYMBOL(__cputime_sec_factor);
u64 __cputime_clockt_factor;
EXPORT_SYMBOL(__cputime_clockt_factor);
DEFINE_PER_CPU(unsigned long, cputime_last_delta);
DEFINE_PER_CPU(unsigned long, cputime_scaled_last_delta);

static void calc_cputime_factors(void)
{
        struct div_result res;

        div128_by_32(HZ, 0, tb_ticks_per_sec, &res);
        __cputime_jiffies_factor = res.result_low;
        div128_by_32(1000, 0, tb_ticks_per_sec, &res);
        __cputime_msec_factor = res.result_low;
        div128_by_32(1, 0, tb_ticks_per_sec, &res);
        __cputime_sec_factor = res.result_low;
        div128_by_32(USER_HZ, 0, tb_ticks_per_sec, &res);
        __cputime_clockt_factor = res.result_low;
}

/*
 * Read the PURR on systems that have it, otherwise the timebase.
 */
static u64 read_purr(void)
{
        if (cpu_has_feature(CPU_FTR_PURR))
                return mfspr(SPRN_PURR);
        return mftb();
}

/*
 * Read the SPURR on systems that have it, otherwise the purr
 */
static u64 read_spurr(u64 purr)
{
        /*
         * cpus without PURR won't have a SPURR
         * We already know the former when we use this, so tell gcc
         */
        if (cpu_has_feature(CPU_FTR_PURR) && cpu_has_feature(CPU_FTR_SPURR))
                return mfspr(SPRN_SPURR);
        return purr;
}

/*
 * Account time for a transition between system, hard irq
 * or soft irq state.
 */
void account_system_vtime(struct task_struct *tsk)
{
        u64 now, nowscaled, delta, deltascaled, sys_time;
        unsigned long flags;

        local_irq_save(flags);
        now = read_purr();
        nowscaled = read_spurr(now);
        delta = now - get_paca()->startpurr;
        deltascaled = nowscaled - get_paca()->startspurr;
        get_paca()->startpurr = now;
        get_paca()->startspurr = nowscaled;
        if (!in_interrupt()) {
                /* deltascaled includes both user and system time.
                 * Hence scale it based on the purr ratio to estimate
                 * the system time */
                sys_time = get_paca()->system_time;
                if (get_paca()->user_time)
                        deltascaled = deltascaled * sys_time /
                             (sys_time + get_paca()->user_time);
                delta += sys_time;
                get_paca()->system_time = 0;
        }
        if (in_irq() || idle_task(smp_processor_id()) != tsk)
                account_system_time(tsk, 0, delta, deltascaled);
        else
                account_idle_time(delta);
        per_cpu(cputime_last_delta, smp_processor_id()) = delta;
        per_cpu(cputime_scaled_last_delta, smp_processor_id()) = deltascaled;
        local_irq_restore(flags);
}

/*
 * Transfer the user and system times accumulated in the paca
 * by the exception entry and exit code to the generic process
 * user and system time records.
 * Must be called with interrupts disabled.
 */
void account_process_tick(struct task_struct *tsk, int user_tick)
{
        cputime_t utime, utimescaled;

        utime = get_paca()->user_time;
        get_paca()->user_time = 0;
        utimescaled = cputime_to_scaled(utime);
        account_user_time(tsk, utime, utimescaled);
}

/*
 * Stuff for accounting stolen time.
 */
struct cpu_purr_data {
        int     initialized;                    /* thread is running */
        u64     tb;                     /* last TB value read */
        u64     purr;                   /* last PURR value read */
        u64     spurr;                  /* last SPURR value read */
};

/*
 * Each entry in the cpu_purr_data array is manipulated only by its
 * "owner" cpu -- usually in the timer interrupt but also occasionally
 * in process context for cpu online.  As long as cpus do not touch
 * each others' cpu_purr_data, disabling local interrupts is
 * sufficient to serialize accesses.
 */
static DEFINE_PER_CPU(struct cpu_purr_data, cpu_purr_data);

static void snapshot_tb_and_purr(void *data)
{
        unsigned long flags;
        struct cpu_purr_data *p = &__get_cpu_var(cpu_purr_data);

        local_irq_save(flags);
        p->tb = get_tb_or_rtc();
        p->purr = mfspr(SPRN_PURR);
        wmb();
        p->initialized = 1;
        local_irq_restore(flags);
}

/*
 * Called during boot when all cpus have come up.
 */
void snapshot_timebases(void)
{
        if (!cpu_has_feature(CPU_FTR_PURR))
                return;
        on_each_cpu(snapshot_tb_and_purr, NULL, 1);
}

/*
 * Must be called with interrupts disabled.
 */
void calculate_steal_time(void)
{
        u64 tb, purr;
        s64 stolen;
        struct cpu_purr_data *pme;

        pme = &__get_cpu_var(cpu_purr_data);
        if (!pme->initialized)
                return;         /* !CPU_FTR_PURR or early in early boot */
        tb = mftb();
        purr = mfspr(SPRN_PURR);
        stolen = (tb - pme->tb) - (purr - pme->purr);
        if (stolen > 0) {
                if (idle_task(smp_processor_id()) != current)
                        account_steal_time(stolen);
                else
                        account_idle_time(stolen);
        }
        pme->tb = tb;
        pme->purr = purr;
}

#ifdef CONFIG_PPC_SPLPAR
/*
 * Must be called before the cpu is added to the online map when
 * a cpu is being brought up at runtime.
 */
static void snapshot_purr(void)
{
        struct cpu_purr_data *pme;
        unsigned long flags;

        if (!cpu_has_feature(CPU_FTR_PURR))
                return;
        local_irq_save(flags);
        pme = &__get_cpu_var(cpu_purr_data);
        pme->tb = mftb();
        pme->purr = mfspr(SPRN_PURR);
        pme->initialized = 1;
        local_irq_restore(flags);
}

#endif /* CONFIG_PPC_SPLPAR */

#else /* ! CONFIG_VIRT_CPU_ACCOUNTING */
#define calc_cputime_factors()
#define calculate_steal_time()          do { } while (0)
#endif

#if !(defined(CONFIG_VIRT_CPU_ACCOUNTING) && defined(CONFIG_PPC_SPLPAR))
#define snapshot_purr()                 do { } while (0)
#endif

/*
 * Called when a cpu comes up after the system has finished booting,
 * i.e. as a result of a hotplug cpu action.
 */
void snapshot_timebase(void)
{
        __get_cpu_var(last_jiffy) = get_tb_or_rtc();
        snapshot_purr();
}

void __delay(unsigned long loops)
{
        unsigned long start;
        int diff;

        if (__USE_RTC()) {
                start = get_rtcl();
                do {
                        /* the RTCL register wraps at 1000000000 */
                        diff = get_rtcl() - start;
                        if (diff < 0)
                                diff += 1000000000;
                } while (diff < loops);
        } else {
                start = get_tbl();
                while (get_tbl() - start < loops)
                        HMT_low();
                HMT_medium();
        }
}
EXPORT_SYMBOL(__delay);

void udelay(unsigned long usecs)
{
        __delay(tb_ticks_per_usec * usecs);
}
EXPORT_SYMBOL(udelay);

static inline void update_gtod(u64 new_tb_stamp, u64 new_stamp_xsec,
                               u64 new_tb_to_xs)
{
        /*
         * tb_update_count is used to allow the userspace gettimeofday code
         * to assure itself that it sees a consistent view of the tb_to_xs and
         * stamp_xsec variables.  It reads the tb_update_count, then reads
         * tb_to_xs and stamp_xsec and then reads tb_update_count again.  If
         * the two values of tb_update_count match and are even then the
         * tb_to_xs and stamp_xsec values are consistent.  If not, then it
         * loops back and reads them again until this criteria is met.
         * We expect the caller to have done the first increment of
         * vdso_data->tb_update_count already.
         */
        vdso_data->tb_orig_stamp = new_tb_stamp;
        vdso_data->stamp_xsec = new_stamp_xsec;
        vdso_data->tb_to_xs = new_tb_to_xs;
        vdso_data->wtom_clock_sec = wall_to_monotonic.tv_sec;
        vdso_data->wtom_clock_nsec = wall_to_monotonic.tv_nsec;
        vdso_data->stamp_xtime = xtime;
        smp_wmb();
        ++(vdso_data->tb_update_count);
}

#ifdef CONFIG_SMP
unsigned long profile_pc(struct pt_regs *regs)
{
        unsigned long pc = instruction_pointer(regs);

        if (in_lock_functions(pc))
                return regs->link;

        return pc;
}
EXPORT_SYMBOL(profile_pc);
#endif

#ifdef CONFIG_PPC_ISERIES

/* 
 * This function recalibrates the timebase based on the 49-bit time-of-day
 * value in the Titan chip.  The Titan is much more accurate than the value
 * returned by the service processor for the timebase frequency.  
 */

static int __init iSeries_tb_recal(void)
{
        struct div_result divres;
        unsigned long titan, tb;

        /* Make sure we only run on iSeries */
        if (!firmware_has_feature(FW_FEATURE_ISERIES))
                return -ENODEV;

        tb = get_tb();
        titan = HvCallXm_loadTod();
        if ( iSeries_recal_titan ) {
                unsigned long tb_ticks = tb - iSeries_recal_tb;
                unsigned long titan_usec = (titan - iSeries_recal_titan) >> 12;
                unsigned long new_tb_ticks_per_sec   = (tb_ticks * USEC_PER_SEC)/titan_usec;
                unsigned long new_tb_ticks_per_jiffy = (new_tb_ticks_per_sec+(HZ/2))/HZ;
                long tick_diff = new_tb_ticks_per_jiffy - tb_ticks_per_jiffy;
                char sign = '+';                
                /* make sure tb_ticks_per_sec and tb_ticks_per_jiffy are consistent */
                new_tb_ticks_per_sec = new_tb_ticks_per_jiffy * HZ;

                if ( tick_diff < 0 ) {
                        tick_diff = -tick_diff;
                        sign = '-';
                }
                if ( tick_diff ) {
                        if ( tick_diff < tb_ticks_per_jiffy/25 ) {
                                printk( "Titan recalibrate: new tb_ticks_per_jiffy = %lu (%c%ld)\n",
                                                new_tb_ticks_per_jiffy, sign, tick_diff );
                                tb_ticks_per_jiffy = new_tb_ticks_per_jiffy;
                                tb_ticks_per_sec   = new_tb_ticks_per_sec;
                                calc_cputime_factors();
                                div128_by_32( XSEC_PER_SEC, 0, tb_ticks_per_sec, &divres );
                                tb_to_xs = divres.result_low;
                                vdso_data->tb_ticks_per_sec = tb_ticks_per_sec;
                                vdso_data->tb_to_xs = tb_to_xs;
                        }
                        else {
                                printk( "Titan recalibrate: FAILED (difference > 4 percent)\n"
                                        "                   new tb_ticks_per_jiffy = %lu\n"
                                        "                   old tb_ticks_per_jiffy = %lu\n",
                                        new_tb_ticks_per_jiffy, tb_ticks_per_jiffy );
                        }
                }
        }
        iSeries_recal_titan = titan;
        iSeries_recal_tb = tb;

        /* Called here as now we know accurate values for the timebase */
        clocksource_init();
        return 0;
}
late_initcall(iSeries_tb_recal);

/* Called from platform early init */
void __init iSeries_time_init_early(void)
{
        iSeries_recal_tb = get_tb();
        iSeries_recal_titan = HvCallXm_loadTod();
}
#endif /* CONFIG_PPC_ISERIES */

/*
 * For iSeries shared processors, we have to let the hypervisor
 * set the hardware decrementer.  We set a virtual decrementer
 * in the lppaca and call the hypervisor if the virtual
 * decrementer is less than the current value in the hardware
 * decrementer. (almost always the new decrementer value will
 * be greater than the current hardware decementer so the hypervisor
 * call will not be needed)
 */

/*
 * timer_interrupt - gets called when the decrementer overflows,
 * with interrupts disabled.
 */
void timer_interrupt(struct pt_regs * regs)
{
        struct pt_regs *old_regs;
        struct decrementer_clock *decrementer =  &__get_cpu_var(decrementers);
        struct clock_event_device *evt = &decrementer->event;
        u64 now;

        /* Ensure a positive value is written to the decrementer, or else
         * some CPUs will continuue to take decrementer exceptions */
        set_dec(DECREMENTER_MAX);

#ifdef CONFIG_PPC32
        if (atomic_read(&ppc_n_lost_interrupts) != 0)
                do_IRQ(regs);
#endif

        now = get_tb_or_rtc();
        if (now < decrementer->next_tb) {
                /* not time for this event yet */
                now = decrementer->next_tb - now;
                if (now <= DECREMENTER_MAX)
                        set_dec((int)now);
                return;
        }
        old_regs = set_irq_regs(regs);
        irq_enter();

        calculate_steal_time();

#ifdef CONFIG_PPC_ISERIES
        if (firmware_has_feature(FW_FEATURE_ISERIES))
                get_lppaca()->int_dword.fields.decr_int = 0;
#endif

        if (evt->event_handler)
                evt->event_handler(evt);

#ifdef CONFIG_PPC_ISERIES
        if (firmware_has_feature(FW_FEATURE_ISERIES) && hvlpevent_is_pending())
                process_hvlpevents();
#endif

#ifdef CONFIG_PPC64
        /* collect purr register values often, for accurate calculations */
        if (firmware_has_feature(FW_FEATURE_SPLPAR)) {
                struct cpu_usage *cu = &__get_cpu_var(cpu_usage_array);
                cu->current_tb = mfspr(SPRN_PURR);
        }
#endif

        irq_exit();
        set_irq_regs(old_regs);
}

void wakeup_decrementer(void)
{
        unsigned long ticks;

        /*
         * The timebase gets saved on sleep and restored on wakeup,
         * so all we need to do is to reset the decrementer.
         */
        ticks = tb_ticks_since(__get_cpu_var(last_jiffy));
        if (ticks < tb_ticks_per_jiffy)
                ticks = tb_ticks_per_jiffy - ticks;
        else
                ticks = 1;
        set_dec(ticks);
}

#ifdef CONFIG_SUSPEND
void generic_suspend_disable_irqs(void)
{
        preempt_disable();

        /* Disable the decrementer, so that it doesn't interfere
         * with suspending.
         */

        set_dec(0x7fffffff);
        local_irq_disable();
        set_dec(0x7fffffff);
}

void generic_suspend_enable_irqs(void)
{
        wakeup_decrementer();

        local_irq_enable();
        preempt_enable();
}

/* Overrides the weak version in kernel/power/main.c */
void arch_suspend_disable_irqs(void)
{
        if (ppc_md.suspend_disable_irqs)
                ppc_md.suspend_disable_irqs();
        generic_suspend_disable_irqs();
}

/* Overrides the weak version in kernel/power/main.c */
void arch_suspend_enable_irqs(void)
{
        generic_suspend_enable_irqs();
        if (ppc_md.suspend_enable_irqs)
                ppc_md.suspend_enable_irqs();
}
#endif

#ifdef CONFIG_SMP
void __init smp_space_timers(unsigned int max_cpus)
{
        int i;
        u64 previous_tb = per_cpu(last_jiffy, boot_cpuid);

        /* make sure tb > per_cpu(last_jiffy, cpu) for all cpus always */
        previous_tb -= tb_ticks_per_jiffy;

        for_each_possible_cpu(i) {
                if (i == boot_cpuid)
                        continue;
                per_cpu(last_jiffy, i) = previous_tb;
        }
}
#endif

/*
 * Scheduler clock - returns current time in nanosec units.
 *
 * Note: mulhdu(a, b) (multiply high double unsigned) returns
 * the high 64 bits of a * b, i.e. (a * b) >> 64, where a and b
 * are 64-bit unsigned numbers.
 */
unsigned long long sched_clock(void)
{
        if (__USE_RTC())
                return get_rtc();
        return mulhdu(get_tb() - boot_tb, tb_to_ns_scale) << tb_to_ns_shift;
}

static int __init get_freq(char *name, int cells, unsigned long *val)
{
        struct device_node *cpu;
        const unsigned int *fp;
        int found = 0;

        /* The cpu node should have timebase and clock frequency properties */
        cpu = of_find_node_by_type(NULL, "cpu");

        if (cpu) {
                fp = of_get_property(cpu, name, NULL);
                if (fp) {
                        found = 1;
                        *val = of_read_ulong(fp, cells);
                }

                of_node_put(cpu);
        }

        return found;
}

void __init generic_calibrate_decr(void)
{
        ppc_tb_freq = DEFAULT_TB_FREQ;          /* hardcoded default */

        if (!get_freq("ibm,extended-timebase-frequency", 2, &ppc_tb_freq) &&
            !get_freq("timebase-frequency", 1, &ppc_tb_freq)) {

                printk(KERN_ERR "WARNING: Estimating decrementer frequency "
                                "(not found)\n");
        }

        ppc_proc_freq = DEFAULT_PROC_FREQ;      /* hardcoded default */

        if (!get_freq("ibm,extended-clock-frequency", 2, &ppc_proc_freq) &&
            !get_freq("clock-frequency", 1, &ppc_proc_freq)) {

                printk(KERN_ERR "WARNING: Estimating processor frequency "
                                "(not found)\n");
        }

#if defined(CONFIG_BOOKE) || defined(CONFIG_40x)
        /* Clear any pending timer interrupts */
        mtspr(SPRN_TSR, TSR_ENW | TSR_WIS | TSR_DIS | TSR_FIS);

        /* Enable decrementer interrupt */
        mtspr(SPRN_TCR, TCR_DIE);
#endif
}

int update_persistent_clock(struct timespec now)
{
        struct rtc_time tm;

        if (!ppc_md.set_rtc_time)
                return 0;

        to_tm(now.tv_sec + 1 + timezone_offset, &tm);
        tm.tm_year -= 1900;
        tm.tm_mon -= 1;

        return ppc_md.set_rtc_time(&tm);
}

unsigned long read_persistent_clock(void)
{
        struct rtc_time tm;
        static int first = 1;

        /* XXX this is a litle fragile but will work okay in the short term */
        if (first) {
                first = 0;
                if (ppc_md.time_init)
                        timezone_offset = ppc_md.time_init();

                /* get_boot_time() isn't guaranteed to be safe to call late */
                if (ppc_md.get_boot_time)
                        return ppc_md.get_boot_time() -timezone_offset;
        }
        if (!ppc_md.get_rtc_time)
                return 0;
        ppc_md.get_rtc_time(&tm);
        return mktime(tm.tm_year+1900, tm.tm_mon+1, tm.tm_mday,
                      tm.tm_hour, tm.tm_min, tm.tm_sec);
}

/* clocksource code */
static cycle_t rtc_read(void)
{
        return (cycle_t)get_rtc();
}

static cycle_t timebase_read(void)
{
        return (cycle_t)get_tb();
}

void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
{
        u64 t2x, stamp_xsec;

        if (clock != &clocksource_timebase)
                return;

        /* Make userspace gettimeofday spin until we're done. */
        ++vdso_data->tb_update_count;
        smp_mb();

        /* XXX this assumes clock->shift == 22 */
        /* 4611686018 ~= 2^(20+64-22) / 1e9 */
        t2x = (u64) clock->mult * 4611686018ULL;
        stamp_xsec = (u64) xtime.tv_nsec * XSEC_PER_SEC;
        do_div(stamp_xsec, 1000000000);
        stamp_xsec += (u64) xtime.tv_sec * XSEC_PER_SEC;
        update_gtod(clock->cycle_last, stamp_xsec, t2x);
}

void update_vsyscall_tz(void)
{
        /* Make userspace gettimeofday spin until we're done. */
        ++vdso_data->tb_update_count;
        smp_mb();
        vdso_data->tz_minuteswest = sys_tz.tz_minuteswest;
        vdso_data->tz_dsttime = sys_tz.tz_dsttime;
        smp_mb();
        ++vdso_data->tb_update_count;
}

static void __init clocksource_init(void)
{
        struct clocksource *clock;

        if (__USE_RTC())
                clock = &clocksource_rtc;
        else
                clock = &clocksource_timebase;

        clock->mult = clocksource_hz2mult(tb_ticks_per_sec, clock->shift);

        if (clocksource_register(clock)) {
                printk(KERN_ERR "clocksource: %s is already registered\n",
                       clock->name);
                return;
        }

        printk(KERN_INFO "clocksource: %s mult[%x] shift[%d] registered\n",
               clock->name, clock->mult, clock->shift);
}

static int decrementer_set_next_event(unsigned long evt,
                                      struct clock_event_device *dev)
{
        __get_cpu_var(decrementers).next_tb = get_tb_or_rtc() + evt;
        set_dec(evt);
        return 0;
}

static void decrementer_set_mode(enum clock_event_mode mode,
                                 struct clock_event_device *dev)
{
        if (mode != CLOCK_EVT_MODE_ONESHOT)
                decrementer_set_next_event(DECREMENTER_MAX, dev);
}

static void register_decrementer_clockevent(int cpu)
{
        struct clock_event_device *dec = &per_cpu(decrementers, cpu).event;

        *dec = decrementer_clockevent;
        dec->cpumask = cpumask_of(cpu);

        printk(KERN_DEBUG "clockevent: %s mult[%lx] shift[%d] cpu[%d]\n",
               dec->name, dec->mult, dec->shift, cpu);

        clockevents_register_device(dec);
}

static void __init init_decrementer_clockevent(void)
{
        int cpu = smp_processor_id();

        decrementer_clockevent.mult = div_sc(ppc_tb_freq, NSEC_PER_SEC,
                                             decrementer_clockevent.shift);
        decrementer_clockevent.max_delta_ns =
                clockevent_delta2ns(DECREMENTER_MAX, &decrementer_clockevent);
        decrementer_clockevent.min_delta_ns =
                clockevent_delta2ns(2, &decrementer_clockevent);

        register_decrementer_clockevent(cpu);
}

void secondary_cpu_time_init(void)
{
        /* FIME: Should make unrelatred change to move snapshot_timebase
         * call here ! */
        register_decrementer_clockevent(smp_processor_id());
}

/* This function is only called on the boot processor */
void __init time_init(void)
{
        unsigned long flags;
        struct div_result res;
        u64 scale, x;
        unsigned shift;

        if (__USE_RTC()) {
                /* 601 processor: dec counts down by 128 every 128ns */
                ppc_tb_freq = 1000000000;
                tb_last_jiffy = get_rtcl();
        } else {
                /* Normal PowerPC with timebase register */
                ppc_md.calibrate_decr();
                printk(KERN_DEBUG "time_init: decrementer frequency = %lu.%.6lu MHz\n",
                       ppc_tb_freq / 1000000, ppc_tb_freq % 1000000);
                printk(KERN_DEBUG "time_init: processor frequency   = %lu.%.6lu MHz\n",
                       ppc_proc_freq / 1000000, ppc_proc_freq % 1000000);
                tb_last_jiffy = get_tb();
        }

        tb_ticks_per_jiffy = ppc_tb_freq / HZ;
        tb_ticks_per_sec = ppc_tb_freq;
        tb_ticks_per_usec = ppc_tb_freq / 1000000;
        tb_to_us = mulhwu_scale_factor(ppc_tb_freq, 1000000);
        calc_cputime_factors();

        /*
         * Calculate the length of each tick in ns.  It will not be
         * exactly 1e9/HZ unless ppc_tb_freq is divisible by HZ.
         * We compute 1e9 * tb_ticks_per_jiffy / ppc_tb_freq,
         * rounded up.
         */
        x = (u64) NSEC_PER_SEC * tb_ticks_per_jiffy + ppc_tb_freq - 1;
        do_div(x, ppc_tb_freq);
        tick_nsec = x;
        last_tick_len = x << TICKLEN_SCALE;

        /*
         * Compute ticklen_to_xs, which is a factor which gets multiplied
         * by (last_tick_len << TICKLEN_SHIFT) to get a tb_to_xs value.
         * It is computed as:
         * ticklen_to_xs = 2^N / (tb_ticks_per_jiffy * 1e9)
         * where N = 64 + 20 - TICKLEN_SCALE - TICKLEN_SHIFT
         * which turns out to be N = 51 - SHIFT_HZ.
         * This gives the result as a 0.64 fixed-point fraction.
         * That value is reduced by an offset amounting to 1 xsec per
         * 2^31 timebase ticks to avoid problems with time going backwards
         * by 1 xsec when we do timer_recalc_offset due to losing the
         * fractional xsec.  That offset is equal to ppc_tb_freq/2^51
         * since there are 2^20 xsec in a second.
         */
        div128_by_32((1ULL << 51) - ppc_tb_freq, 0,
                     tb_ticks_per_jiffy << SHIFT_HZ, &res);
        div128_by_32(res.result_high, res.result_low, NSEC_PER_SEC, &res);
        ticklen_to_xs = res.result_low;

        /* Compute tb_to_xs from tick_nsec */
        tb_to_xs = mulhdu(last_tick_len << TICKLEN_SHIFT, ticklen_to_xs);

        /*
         * Compute scale factor for sched_clock.
         * The calibrate_decr() function has set tb_ticks_per_sec,
         * which is the timebase frequency.
         * We compute 1e9 * 2^64 / tb_ticks_per_sec and interpret
         * the 128-bit result as a 64.64 fixed-point number.
         * We then shift that number right until it is less than 1.0,
         * giving us the scale factor and shift count to use in
         * sched_clock().
         */
        div128_by_32(1000000000, 0, tb_ticks_per_sec, &res);
        scale = res.result_low;
        for (shift = 0; res.result_high != 0; ++shift) {
                scale = (scale >> 1) | (res.result_high << 63);
                res.result_high >>= 1;
        }
        tb_to_ns_scale = scale;
        tb_to_ns_shift = shift;
        /* Save the current timebase to pretty up CONFIG_PRINTK_TIME */
        boot_tb = get_tb_or_rtc();

        write_seqlock_irqsave(&xtime_lock, flags);

        /* If platform provided a timezone (pmac), we correct the time */
        if (timezone_offset) {
                sys_tz.tz_minuteswest = -timezone_offset / 60;
                sys_tz.tz_dsttime = 0;
        }

        vdso_data->tb_orig_stamp = tb_last_jiffy;
        vdso_data->tb_update_count = 0;
        vdso_data->tb_ticks_per_sec = tb_ticks_per_sec;
        vdso_data->stamp_xsec = (u64) xtime.tv_sec * XSEC_PER_SEC;
        vdso_data->tb_to_xs = tb_to_xs;

        write_sequnlock_irqrestore(&xtime_lock, flags);

        /* Register the clocksource, if we're not running on iSeries */
        if (!firmware_has_feature(FW_FEATURE_ISERIES))
                clocksource_init();

        init_decrementer_clockevent();
}


#define FEBRUARY        2
#define STARTOFTIME     1970
#define SECDAY          86400L
#define SECYR           (SECDAY * 365)
#define leapyear(year)          ((year) % 4 == 0 && \
                                 ((year) % 100 != 0 || (year) % 400 == 0))
#define days_in_year(a)         (leapyear(a) ? 366 : 365)
#define days_in_month(a)        (month_days[(a) - 1])

static int month_days[12] = {
        31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};

/*
 * This only works for the Gregorian calendar - i.e. after 1752 (in the UK)
 */
void GregorianDay(struct rtc_time * tm)
{
        int leapsToDate;
        int lastYear;
        int day;
        int MonthOffset[] = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 };

        lastYear = tm->tm_year - 1;

        /*
         * Number of leap corrections to apply up to end of last year
         */
        leapsToDate = lastYear / 4 - lastYear / 100 + lastYear / 400;

        /*
         * This year is a leap year if it is divisible by 4 except when it is
         * divisible by 100 unless it is divisible by 400
         *
         * e.g. 1904 was a leap year, 1900 was not, 1996 is, and 2000 was
         */
        day = tm->tm_mon > 2 && leapyear(tm->tm_year);

        day += lastYear*365 + leapsToDate + MonthOffset[tm->tm_mon-1] +
                   tm->tm_mday;

        tm->tm_wday = day % 7;
}

void to_tm(int tim, struct rtc_time * tm)
{
        register int    i;
        register long   hms, day;

        day = tim / SECDAY;
        hms = tim % SECDAY;

        /* Hours, minutes, seconds are easy */
        tm->tm_hour = hms / 3600;
        tm->tm_min = (hms % 3600) / 60;
        tm->tm_sec = (hms % 3600) % 60;

        /* Number of years in days */
        for (i = STARTOFTIME; day >= days_in_year(i); i++)
                day -= days_in_year(i);
        tm->tm_year = i;

        /* Number of months in days left */
        if (leapyear(tm->tm_year))
                days_in_month(FEBRUARY) = 29;
        for (i = 1; day >= days_in_month(i); i++)
                day -= days_in_month(i);
        days_in_month(FEBRUARY) = 28;
        tm->tm_mon = i;

        /* Days are what is left over (+1) from all that. */
        tm->tm_mday = day + 1;

        /*
         * Determine the day of week
         */
        GregorianDay(tm);
}

/* Auxiliary function to compute scaling factors */
/* Actually the choice of a timebase running at 1/4 the of the bus
 * frequency giving resolution of a few tens of nanoseconds is quite nice.
 * It makes this computation very precise (27-28 bits typically) which
 * is optimistic considering the stability of most processor clock
 * oscillators and the precision with which the timebase frequency
 * is measured but does not harm.
 */
unsigned mulhwu_scale_factor(unsigned inscale, unsigned outscale)
{
        unsigned mlt=0, tmp, err;
        /* No concern for performance, it's done once: use a stupid
         * but safe and compact method to find the multiplier.
         */
  
        for (tmp = 1U<<31; tmp != 0; tmp >>= 1) {
                if (mulhwu(inscale, mlt|tmp) < outscale)
                        mlt |= tmp;
        }
  
        /* We might still be off by 1 for the best approximation.
         * A side effect of this is that if outscale is too large
         * the returned value will be zero.
         * Many corner cases have been checked and seem to work,
         * some might have been forgotten in the test however.
         */
  
        err = inscale * (mlt+1);
        if (err <= inscale/2)
                mlt++;
        return mlt;
}

/*
 * Divide a 128-bit dividend by a 32-bit divisor, leaving a 128 bit
 * result.
 */
void div128_by_32(u64 dividend_high, u64 dividend_low,
                  unsigned divisor, struct div_result *dr)
{
        unsigned long a, b, c, d;
        unsigned long w, x, y, z;
        u64 ra, rb, rc;

        a = dividend_high >> 32;
        b = dividend_high & 0xffffffff;
        c = dividend_low >> 32;
        d = dividend_low & 0xffffffff;

        w = a / divisor;
        ra = ((u64)(a - (w * divisor)) << 32) + b;

        rb = ((u64) do_div(ra, divisor) << 32) + c;
        x = ra;

        rc = ((u64) do_div(rb, divisor) << 32) + d;
        y = rb;

        do_div(rc, divisor);
        z = rc;

        dr->result_high = ((u64)w << 32) + x;
        dr->result_low  = ((u64)y << 32) + z;

}

static int __init rtc_init(void)
{
        struct platform_device *pdev;

        if (!ppc_md.get_rtc_time)
                return -ENODEV;

        pdev = platform_device_register_simple("rtc-generic", -1, NULL, 0);
        if (IS_ERR(pdev))
                return PTR_ERR(pdev);

        return 0;
}

module_init(rtc_init);