time.c

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/*
 *    Time of day based timer functions.
 *
 *  S390 version
 *    Copyright IBM Corp. 1999, 2008
 *    Author(s): Hartmut Penner ([email protected]),
 *               Martin Schwidefsky ([email protected]),
 *               Denis Joseph Barrow ([email protected],[email protected])
 *
 *  Derived from "arch/i386/kernel/time.c"
 *    Copyright (C) 1991, 1992, 1995  Linus Torvalds
 */

#define KMSG_COMPONENT "time"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#include <linux/kernel_stat.h>
#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/cpu.h>
#include <linux/stop_machine.h>
#include <linux/time.h>
#include <linux/device.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/types.h>
#include <linux/profile.h>
#include <linux/timex.h>
#include <linux/notifier.h>
#include <linux/timekeeper_internal.h>
#include <linux/clockchips.h>
#include <linux/gfp.h>
#include <linux/kprobes.h>
#include <asm/uaccess.h>
#include <asm/delay.h>
#include <asm/div64.h>
#include <asm/vdso.h>
#include <asm/irq.h>
#include <asm/irq_regs.h>
#include <asm/vtimer.h>
#include <asm/etr.h>
#include <asm/cio.h>
#include "entry.h"

/* change this if you have some constant time drift */
#define USECS_PER_JIFFY     ((unsigned long) 1000000/HZ)
#define CLK_TICKS_PER_JIFFY ((unsigned long) USECS_PER_JIFFY << 12)

u64 sched_clock_base_cc = -1;   /* Force to data section. */
EXPORT_SYMBOL_GPL(sched_clock_base_cc);

static DEFINE_PER_CPU(struct clock_event_device, comparators);

/*
 * Scheduler clock - returns current time in nanosec units.
 */
unsigned long long notrace __kprobes sched_clock(void)
{
    return (get_clock_monotonic() * 125) >> 9;
}

/*
 * Monotonic_clock - returns # of nanoseconds passed since time_init()
 */
unsigned long long monotonic_clock(void)
{
    return sched_clock();
}
EXPORT_SYMBOL(monotonic_clock);

void tod_to_timeval(__u64 todval, struct timespec *xt)
{
    unsigned long long sec;

    sec = todval >> 12;
    do_div(sec, 1000000);
    xt->tv_sec = sec;
    todval -= (sec * 1000000) << 12;
    xt->tv_nsec = ((todval * 1000) >> 12);
}
EXPORT_SYMBOL(tod_to_timeval);

void clock_comparator_work(void)
{
    struct clock_event_device *cd;

    S390_lowcore.clock_comparator = -1ULL;
    set_clock_comparator(S390_lowcore.clock_comparator);
    cd = &__get_cpu_var(comparators);
    cd->event_handler(cd);
}

/*
 * Fixup the clock comparator.
 */
static void fixup_clock_comparator(unsigned long long delta)
{
    /* If nobody is waiting there's nothing to fix. */
    if (S390_lowcore.clock_comparator == -1ULL)
        return;
    S390_lowcore.clock_comparator += delta;
    set_clock_comparator(S390_lowcore.clock_comparator);
}

static int s390_next_ktime(ktime_t expires,
               struct clock_event_device *evt)
{
    struct timespec ts;
    u64 nsecs;

    ts.tv_sec = ts.tv_nsec = 0;
    monotonic_to_bootbased(&ts);
    nsecs = ktime_to_ns(ktime_add(timespec_to_ktime(ts), expires));
    do_div(nsecs, 125);
    S390_lowcore.clock_comparator = sched_clock_base_cc + (nsecs << 9);
    set_clock_comparator(S390_lowcore.clock_comparator);
    return 0;
}

static void s390_set_mode(enum clock_event_mode mode,
              struct clock_event_device *evt)
{
}

/*
 * Set up lowcore and control register of the current cpu to
 * enable TOD clock and clock comparator interrupts.
 */
void init_cpu_timer(void)
{
    struct clock_event_device *cd;
    int cpu;

    S390_lowcore.clock_comparator = -1ULL;
    set_clock_comparator(S390_lowcore.clock_comparator);

    cpu = smp_processor_id();
    cd = &per_cpu(comparators, cpu);
    cd->name        = "comparator";
    cd->features        = CLOCK_EVT_FEAT_ONESHOT |
                  CLOCK_EVT_FEAT_KTIME;
    cd->mult        = 16777;
    cd->shift       = 12;
    cd->min_delta_ns    = 1;
    cd->max_delta_ns    = LONG_MAX;
    cd->rating      = 400;
    cd->cpumask     = cpumask_of(cpu);
    cd->set_next_ktime  = s390_next_ktime;
    cd->set_mode        = s390_set_mode;

    clockevents_register_device(cd);

    /* Enable clock comparator timer interrupt. */
    __ctl_set_bit(0,11);

    /* Always allow the timing alert external interrupt. */
    __ctl_set_bit(0, 4);
}

static void clock_comparator_interrupt(struct ext_code ext_code,
                       unsigned int param32,
                       unsigned long param64)
{
    kstat_cpu(smp_processor_id()).irqs[EXTINT_CLK]++;
    if (S390_lowcore.clock_comparator == -1ULL)
        set_clock_comparator(S390_lowcore.clock_comparator);
}

static void etr_timing_alert(struct etr_irq_parm *);
static void stp_timing_alert(struct stp_irq_parm *);

static void timing_alert_interrupt(struct ext_code ext_code,
                   unsigned int param32, unsigned long param64)
{
    kstat_cpu(smp_processor_id()).irqs[EXTINT_TLA]++;
    if (param32 & 0x00c40000)
        etr_timing_alert((struct etr_irq_parm *) &param32);
    if (param32 & 0x00038000)
        stp_timing_alert((struct stp_irq_parm *) &param32);
}

static void etr_reset(void);
static void stp_reset(void);

void read_persistent_clock(struct timespec *ts)
{
    tod_to_timeval(get_clock() - TOD_UNIX_EPOCH, ts);
}

void read_boot_clock(struct timespec *ts)
{
    tod_to_timeval(sched_clock_base_cc - TOD_UNIX_EPOCH, ts);
}

static cycle_t read_tod_clock(struct clocksource *cs)
{
    return get_clock();
}

static struct clocksource clocksource_tod = {
    .name       = "tod",
    .rating     = 400,
    .read       = read_tod_clock,
    .mask       = -1ULL,
    .mult       = 1000,
    .shift      = 12,
    .flags      = CLOCK_SOURCE_IS_CONTINUOUS,
};

struct clocksource * __init clocksource_default_clock(void)
{
    return &clocksource_tod;
}

void update_vsyscall_old(struct timespec *wall_time, struct timespec *wtm,
            struct clocksource *clock, u32 mult)
{
    if (clock != &clocksource_tod)
        return;

    /* Make userspace gettimeofday spin until we're done. */
    ++vdso_data->tb_update_count;
    smp_wmb();
    vdso_data->xtime_tod_stamp = clock->cycle_last;
    vdso_data->xtime_clock_sec = wall_time->tv_sec;
    vdso_data->xtime_clock_nsec = wall_time->tv_nsec;
    vdso_data->wtom_clock_sec = wtm->tv_sec;
    vdso_data->wtom_clock_nsec = wtm->tv_nsec;
    vdso_data->ntp_mult = mult;
    smp_wmb();
    ++vdso_data->tb_update_count;
}

extern struct timezone sys_tz;

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

/*
 * Initialize the TOD clock and the CPU timer of
 * the boot cpu.
 */
void __init time_init(void)
{
    /* Reset time synchronization interfaces. */
    etr_reset();
    stp_reset();

    /* request the clock comparator external interrupt */
    if (register_external_interrupt(0x1004, clock_comparator_interrupt))
                panic("Couldn't request external interrupt 0x1004");

    /* request the timing alert external interrupt */
    if (register_external_interrupt(0x1406, timing_alert_interrupt))
        panic("Couldn't request external interrupt 0x1406");

    if (clocksource_register(&clocksource_tod) != 0)
        panic("Could not register TOD clock source");

    /* Enable TOD clock interrupts on the boot cpu. */
    init_cpu_timer();

    /* Enable cpu timer interrupts on the boot cpu. */
    vtime_init();
}

/*
 * The time is "clock". old is what we think the time is.
 * Adjust the value by a multiple of jiffies and add the delta to ntp.
 * "delay" is an approximation how long the synchronization took. If
 * the time correction is positive, then "delay" is subtracted from
 * the time difference and only the remaining part is passed to ntp.
 */
static unsigned long long adjust_time(unsigned long long old,
                      unsigned long long clock,
                      unsigned long long delay)
{
    unsigned long long delta, ticks;
    struct timex adjust;

    if (clock > old) {
        /* It is later than we thought. */
        delta = ticks = clock - old;
        delta = ticks = (delta < delay) ? 0 : delta - delay;
        delta -= do_div(ticks, CLK_TICKS_PER_JIFFY);
        adjust.offset = ticks * (1000000 / HZ);
    } else {
        /* It is earlier than we thought. */
        delta = ticks = old - clock;
        delta -= do_div(ticks, CLK_TICKS_PER_JIFFY);
        delta = -delta;
        adjust.offset = -ticks * (1000000 / HZ);
    }
    sched_clock_base_cc += delta;
    if (adjust.offset != 0) {
        pr_notice("The ETR interface has adjusted the clock "
              "by %li microseconds\n", adjust.offset);
        adjust.modes = ADJ_OFFSET_SINGLESHOT;
        do_adjtimex(&adjust);
    }
    return delta;
}

static DEFINE_PER_CPU(atomic_t, clock_sync_word);
static DEFINE_MUTEX(clock_sync_mutex);
static unsigned long clock_sync_flags;

#define CLOCK_SYNC_HAS_ETR  0
#define CLOCK_SYNC_HAS_STP  1
#define CLOCK_SYNC_ETR      2
#define CLOCK_SYNC_STP      3

/*
 * The synchronous get_clock function. It will write the current clock
 * value to the clock pointer and return 0 if the clock is in sync with
 * the external time source. If the clock mode is local it will return
 * -EOPNOTSUPP and -EAGAIN if the clock is not in sync with the external
 * reference.
 */
int get_sync_clock(unsigned long long *clock)
{
    atomic_t *sw_ptr;
    unsigned int sw0, sw1;

    sw_ptr = &get_cpu_var(clock_sync_word);
    sw0 = atomic_read(sw_ptr);
    *clock = get_clock();
    sw1 = atomic_read(sw_ptr);
    put_cpu_var(clock_sync_word);
    if (sw0 == sw1 && (sw0 & 0x80000000U))
        /* Success: time is in sync. */
        return 0;
    if (!test_bit(CLOCK_SYNC_HAS_ETR, &clock_sync_flags) &&
        !test_bit(CLOCK_SYNC_HAS_STP, &clock_sync_flags))
        return -EOPNOTSUPP;
    if (!test_bit(CLOCK_SYNC_ETR, &clock_sync_flags) &&
        !test_bit(CLOCK_SYNC_STP, &clock_sync_flags))
        return -EACCES;
    return -EAGAIN;
}
EXPORT_SYMBOL(get_sync_clock);

/*
 * Make get_sync_clock return -EAGAIN.
 */
static void disable_sync_clock(void *dummy)
{
    atomic_t *sw_ptr = &__get_cpu_var(clock_sync_word);
    /*
     * Clear the in-sync bit 2^31. All get_sync_clock calls will
     * fail until the sync bit is turned back on. In addition
     * increase the "sequence" counter to avoid the race of an
     * etr event and the complete recovery against get_sync_clock.
     */
    atomic_clear_mask(0x80000000, sw_ptr);
    atomic_inc(sw_ptr);
}

/*
 * Make get_sync_clock return 0 again.
 * Needs to be called from a context disabled for preemption.
 */
static void enable_sync_clock(void)
{
    atomic_t *sw_ptr = &__get_cpu_var(clock_sync_word);
    atomic_set_mask(0x80000000, sw_ptr);
}

/*
 * Function to check if the clock is in sync.
 */
static inline int check_sync_clock(void)
{
    atomic_t *sw_ptr;
    int rc;

    sw_ptr = &get_cpu_var(clock_sync_word);
    rc = (atomic_read(sw_ptr) & 0x80000000U) != 0;
    put_cpu_var(clock_sync_word);
    return rc;
}

/* Single threaded workqueue used for etr and stp sync events */
static struct workqueue_struct *time_sync_wq;

static void __init time_init_wq(void)
{
    if (time_sync_wq)
        return;
    time_sync_wq = create_singlethread_workqueue("timesync");
}

/*
 * External Time Reference (ETR) code.
 */
static int etr_port0_online;
static int etr_port1_online;
static int etr_steai_available;

static int __init early_parse_etr(char *p)
{
    if (strncmp(p, "off", 3) == 0)
        etr_port0_online = etr_port1_online = 0;
    else if (strncmp(p, "port0", 5) == 0)
        etr_port0_online = 1;
    else if (strncmp(p, "port1", 5) == 0)
        etr_port1_online = 1;
    else if (strncmp(p, "on", 2) == 0)
        etr_port0_online = etr_port1_online = 1;
    return 0;
}
early_param("etr", early_parse_etr);

enum etr_event {
    ETR_EVENT_PORT0_CHANGE,
    ETR_EVENT_PORT1_CHANGE,
    ETR_EVENT_PORT_ALERT,
    ETR_EVENT_SYNC_CHECK,
    ETR_EVENT_SWITCH_LOCAL,
    ETR_EVENT_UPDATE,
};

/*
 * Valid bit combinations of the eacr register are (x = don't care):
 * e0 e1 dp p0 p1 ea es sl
 *  0  0  x  0  0  0  0  0  initial, disabled state
 *  0  0  x  0  1  1  0  0  port 1 online
 *  0  0  x  1  0  1  0  0  port 0 online
 *  0  0  x  1  1  1  0  0  both ports online
 *  0  1  x  0  1  1  0  0  port 1 online and usable, ETR or PPS mode
 *  0  1  x  0  1  1  0  1  port 1 online, usable and ETR mode
 *  0  1  x  0  1  1  1  0  port 1 online, usable, PPS mode, in-sync
 *  0  1  x  0  1  1  1  1  port 1 online, usable, ETR mode, in-sync
 *  0  1  x  1  1  1  0  0  both ports online, port 1 usable
 *  0  1  x  1  1  1  1  0  both ports online, port 1 usable, PPS mode, in-sync
 *  0  1  x  1  1  1  1  1  both ports online, port 1 usable, ETR mode, in-sync
 *  1  0  x  1  0  1  0  0  port 0 online and usable, ETR or PPS mode
 *  1  0  x  1  0  1  0  1  port 0 online, usable and ETR mode
 *  1  0  x  1  0  1  1  0  port 0 online, usable, PPS mode, in-sync
 *  1  0  x  1  0  1  1  1  port 0 online, usable, ETR mode, in-sync
 *  1  0  x  1  1  1  0  0  both ports online, port 0 usable
 *  1  0  x  1  1  1  1  0  both ports online, port 0 usable, PPS mode, in-sync
 *  1  0  x  1  1  1  1  1  both ports online, port 0 usable, ETR mode, in-sync
 *  1  1  x  1  1  1  1  0  both ports online & usable, ETR, in-sync
 *  1  1  x  1  1  1  1  1  both ports online & usable, ETR, in-sync
 */
static struct etr_eacr etr_eacr;
static u64 etr_tolec;           /* time of last eacr update */
static struct etr_aib etr_port0;
static int etr_port0_uptodate;
static struct etr_aib etr_port1;
static int etr_port1_uptodate;
static unsigned long etr_events;
static struct timer_list etr_timer;

static void etr_timeout(unsigned long dummy);
static void etr_work_fn(struct work_struct *work);
static DEFINE_MUTEX(etr_work_mutex);
static DECLARE_WORK(etr_work, etr_work_fn);

/*
 * Reset ETR attachment.
 */
static void etr_reset(void)
{
    etr_eacr =  (struct etr_eacr) {
        .e0 = 0, .e1 = 0, ._pad0 = 4, .dp = 0,
        .p0 = 0, .p1 = 0, ._pad1 = 0, .ea = 0,
        .es = 0, .sl = 0 };
    if (etr_setr(&etr_eacr) == 0) {
        etr_tolec = get_clock();
        set_bit(CLOCK_SYNC_HAS_ETR, &clock_sync_flags);
        if (etr_port0_online && etr_port1_online)
            set_bit(CLOCK_SYNC_ETR, &clock_sync_flags);
    } else if (etr_port0_online || etr_port1_online) {
        pr_warning("The real or virtual hardware system does "
               "not provide an ETR interface\n");
        etr_port0_online = etr_port1_online = 0;
    }
}

static int __init etr_init(void)
{
    struct etr_aib aib;

    if (!test_bit(CLOCK_SYNC_HAS_ETR, &clock_sync_flags))
        return 0;
    time_init_wq();
    /* Check if this machine has the steai instruction. */
    if (etr_steai(&aib, ETR_STEAI_STEPPING_PORT) == 0)
        etr_steai_available = 1;
    setup_timer(&etr_timer, etr_timeout, 0UL);
    if (etr_port0_online) {
        set_bit(ETR_EVENT_PORT0_CHANGE, &etr_events);
        queue_work(time_sync_wq, &etr_work);
    }
    if (etr_port1_online) {
        set_bit(ETR_EVENT_PORT1_CHANGE, &etr_events);
        queue_work(time_sync_wq, &etr_work);
    }
    return 0;
}

arch_initcall(etr_init);

/*
 * Two sorts of ETR machine checks. The architecture reads:
 * "When a machine-check niterruption occurs and if a switch-to-local or
 *  ETR-sync-check interrupt request is pending but disabled, this pending
 *  disabled interruption request is indicated and is cleared".
 * Which means that we can get etr_switch_to_local events from the machine
 * check handler although the interruption condition is disabled. Lovely..
 */

/*
 * Switch to local machine check. This is called when the last usable
 * ETR port goes inactive. After switch to local the clock is not in sync.
 */
void etr_switch_to_local(void)
{
    if (!etr_eacr.sl)
        return;
    disable_sync_clock(NULL);
    if (!test_and_set_bit(ETR_EVENT_SWITCH_LOCAL, &etr_events)) {
        etr_eacr.es = etr_eacr.sl = 0;
        etr_setr(&etr_eacr);
        queue_work(time_sync_wq, &etr_work);
    }
}

/*
 * ETR sync check machine check. This is called when the ETR OTE and the
 * local clock OTE are farther apart than the ETR sync check tolerance.
 * After a ETR sync check the clock is not in sync. The machine check
 * is broadcasted to all cpus at the same time.
 */
void etr_sync_check(void)
{
    if (!etr_eacr.es)
        return;
    disable_sync_clock(NULL);
    if (!test_and_set_bit(ETR_EVENT_SYNC_CHECK, &etr_events)) {
        etr_eacr.es = 0;
        etr_setr(&etr_eacr);
        queue_work(time_sync_wq, &etr_work);
    }
}

/*
 * ETR timing alert. There are two causes:
 * 1) port state change, check the usability of the port
 * 2) port alert, one of the ETR-data-validity bits (v1-v2 bits of the
 *    sldr-status word) or ETR-data word 1 (edf1) or ETR-data word 3 (edf3)
 *    or ETR-data word 4 (edf4) has changed.
 */
static void etr_timing_alert(struct etr_irq_parm *intparm)
{
    if (intparm->pc0)
        /* ETR port 0 state change. */
        set_bit(ETR_EVENT_PORT0_CHANGE, &etr_events);
    if (intparm->pc1)
        /* ETR port 1 state change. */
        set_bit(ETR_EVENT_PORT1_CHANGE, &etr_events);
    if (intparm->eai)
        /*
         * ETR port alert on either port 0, 1 or both.
         * Both ports are not up-to-date now.
         */
        set_bit(ETR_EVENT_PORT_ALERT, &etr_events);
    queue_work(time_sync_wq, &etr_work);
}

static void etr_timeout(unsigned long dummy)
{
    set_bit(ETR_EVENT_UPDATE, &etr_events);
    queue_work(time_sync_wq, &etr_work);
}

/*
 * Check if the etr mode is pss.
 */
static inline int etr_mode_is_pps(struct etr_eacr eacr)
{
    return eacr.es && !eacr.sl;
}

/*
 * Check if the etr mode is etr.
 */
static inline int etr_mode_is_etr(struct etr_eacr eacr)
{
    return eacr.es && eacr.sl;
}

/*
 * Check if the port can be used for TOD synchronization.
 * For PPS mode the port has to receive OTEs. For ETR mode
 * the port has to receive OTEs, the ETR stepping bit has to
 * be zero and the validity bits for data frame 1, 2, and 3
 * have to be 1.
 */
static int etr_port_valid(struct etr_aib *aib, int port)
{
    unsigned int psc;

    /* Check that this port is receiving OTEs. */
    if (aib->tsp == 0)
        return 0;

    psc = port ? aib->esw.psc1 : aib->esw.psc0;
    if (psc == etr_lpsc_pps_mode)
        return 1;
    if (psc == etr_lpsc_operational_step)
        return !aib->esw.y && aib->slsw.v1 &&
            aib->slsw.v2 && aib->slsw.v3;
    return 0;
}

/*
 * Check if two ports are on the same network.
 */
static int etr_compare_network(struct etr_aib *aib1, struct etr_aib *aib2)
{
    // FIXME: any other fields we have to compare?
    return aib1->edf1.net_id == aib2->edf1.net_id;
}

/*
 * Wrapper for etr_stei that converts physical port states
 * to logical port states to be consistent with the output
 * of stetr (see etr_psc vs. etr_lpsc).
 */
static void etr_steai_cv(struct etr_aib *aib, unsigned int func)
{
    BUG_ON(etr_steai(aib, func) != 0);
    /* Convert port state to logical port state. */
    if (aib->esw.psc0 == 1)
        aib->esw.psc0 = 2;
    else if (aib->esw.psc0 == 0 && aib->esw.p == 0)
        aib->esw.psc0 = 1;
    if (aib->esw.psc1 == 1)
        aib->esw.psc1 = 2;
    else if (aib->esw.psc1 == 0 && aib->esw.p == 1)
        aib->esw.psc1 = 1;
}

/*
 * Check if the aib a2 is still connected to the same attachment as
 * aib a1, the etv values differ by one and a2 is valid.
 */
static int etr_aib_follows(struct etr_aib *a1, struct etr_aib *a2, int p)
{
    int state_a1, state_a2;

    /* Paranoia check: e0/e1 should better be the same. */
    if (a1->esw.eacr.e0 != a2->esw.eacr.e0 ||
        a1->esw.eacr.e1 != a2->esw.eacr.e1)
        return 0;

    /* Still connected to the same etr ? */
    state_a1 = p ? a1->esw.psc1 : a1->esw.psc0;
    state_a2 = p ? a2->esw.psc1 : a2->esw.psc0;
    if (state_a1 == etr_lpsc_operational_step) {
        if (state_a2 != etr_lpsc_operational_step ||
            a1->edf1.net_id != a2->edf1.net_id ||
            a1->edf1.etr_id != a2->edf1.etr_id ||
            a1->edf1.etr_pn != a2->edf1.etr_pn)
            return 0;
    } else if (state_a2 != etr_lpsc_pps_mode)
        return 0;

    /* The ETV value of a2 needs to be ETV of a1 + 1. */
    if (a1->edf2.etv + 1 != a2->edf2.etv)
        return 0;

    if (!etr_port_valid(a2, p))
        return 0;

    return 1;
}

struct clock_sync_data {
    atomic_t cpus;
    int in_sync;
    unsigned long long fixup_cc;
    int etr_port;
    struct etr_aib *etr_aib;
};

static void clock_sync_cpu(struct clock_sync_data *sync)
{
    atomic_dec(&sync->cpus);
    enable_sync_clock();
    /*
     * This looks like a busy wait loop but it isn't. etr_sync_cpus
     * is called on all other cpus while the TOD clocks is stopped.
     * __udelay will stop the cpu on an enabled wait psw until the
     * TOD is running again.
     */
    while (sync->in_sync == 0) {
        __udelay(1);
        /*
         * A different cpu changes *in_sync. Therefore use
         * barrier() to force memory access.
         */
        barrier();
    }
    if (sync->in_sync != 1)
        /* Didn't work. Clear per-cpu in sync bit again. */
        disable_sync_clock(NULL);
    /*
     * This round of TOD syncing is done. Set the clock comparator
     * to the next tick and let the processor continue.
     */
    fixup_clock_comparator(sync->fixup_cc);
}

/*
 * Sync the TOD clock using the port referred to by aibp. This port
 * has to be enabled and the other port has to be disabled. The
 * last eacr update has to be more than 1.6 seconds in the past.
 */
static int etr_sync_clock(void *data)
{
    static int first;
    unsigned long long clock, old_clock, delay, delta;
    struct clock_sync_data *etr_sync;
    struct etr_aib *sync_port, *aib;
    int port;
    int rc;

    etr_sync = data;

    if (xchg(&first, 1) == 1) {
        /* Slave */
        clock_sync_cpu(etr_sync);
        return 0;
    }

    /* Wait until all other cpus entered the sync function. */
    while (atomic_read(&etr_sync->cpus) != 0)
        cpu_relax();

    port = etr_sync->etr_port;
    aib = etr_sync->etr_aib;
    sync_port = (port == 0) ? &etr_port0 : &etr_port1;
    enable_sync_clock();

    /* Set clock to next OTE. */
    __ctl_set_bit(14, 21);
    __ctl_set_bit(0, 29);
    clock = ((unsigned long long) (aib->edf2.etv + 1)) << 32;
    old_clock = get_clock();
    if (set_clock(clock) == 0) {
        __udelay(1);    /* Wait for the clock to start. */
        __ctl_clear_bit(0, 29);
        __ctl_clear_bit(14, 21);
        etr_stetr(aib);
        /* Adjust Linux timing variables. */
        delay = (unsigned long long)
            (aib->edf2.etv - sync_port->edf2.etv) << 32;
        delta = adjust_time(old_clock, clock, delay);
        etr_sync->fixup_cc = delta;
        fixup_clock_comparator(delta);
        /* Verify that the clock is properly set. */
        if (!etr_aib_follows(sync_port, aib, port)) {
            /* Didn't work. */
            disable_sync_clock(NULL);
            etr_sync->in_sync = -EAGAIN;
            rc = -EAGAIN;
        } else {
            etr_sync->in_sync = 1;
            rc = 0;
        }
    } else {
        /* Could not set the clock ?!? */
        __ctl_clear_bit(0, 29);
        __ctl_clear_bit(14, 21);
        disable_sync_clock(NULL);
        etr_sync->in_sync = -EAGAIN;
        rc = -EAGAIN;
    }
    xchg(&first, 0);
    return rc;
}

static int etr_sync_clock_stop(struct etr_aib *aib, int port)
{
    struct clock_sync_data etr_sync;
    struct etr_aib *sync_port;
    int follows;
    int rc;

    /* Check if the current aib is adjacent to the sync port aib. */
    sync_port = (port == 0) ? &etr_port0 : &etr_port1;
    follows = etr_aib_follows(sync_port, aib, port);
    memcpy(sync_port, aib, sizeof(*aib));
    if (!follows)
        return -EAGAIN;
    memset(&etr_sync, 0, sizeof(etr_sync));
    etr_sync.etr_aib = aib;
    etr_sync.etr_port = port;
    get_online_cpus();
    atomic_set(&etr_sync.cpus, num_online_cpus() - 1);
    rc = stop_machine(etr_sync_clock, &etr_sync, cpu_online_mask);
    put_online_cpus();
    return rc;
}

/*
 * Handle the immediate effects of the different events.
 * The port change event is used for online/offline changes.
 */
static struct etr_eacr etr_handle_events(struct etr_eacr eacr)
{
    if (test_and_clear_bit(ETR_EVENT_SYNC_CHECK, &etr_events))
        eacr.es = 0;
    if (test_and_clear_bit(ETR_EVENT_SWITCH_LOCAL, &etr_events))
        eacr.es = eacr.sl = 0;
    if (test_and_clear_bit(ETR_EVENT_PORT_ALERT, &etr_events))
        etr_port0_uptodate = etr_port1_uptodate = 0;

    if (test_and_clear_bit(ETR_EVENT_PORT0_CHANGE, &etr_events)) {
        if (eacr.e0)
            /*
             * Port change of an enabled port. We have to
             * assume that this can have caused an stepping
             * port switch.
             */
            etr_tolec = get_clock();
        eacr.p0 = etr_port0_online;
        if (!eacr.p0)
            eacr.e0 = 0;
        etr_port0_uptodate = 0;
    }
    if (test_and_clear_bit(ETR_EVENT_PORT1_CHANGE, &etr_events)) {
        if (eacr.e1)
            /*
             * Port change of an enabled port. We have to
             * assume that this can have caused an stepping
             * port switch.
             */
            etr_tolec = get_clock();
        eacr.p1 = etr_port1_online;
        if (!eacr.p1)
            eacr.e1 = 0;
        etr_port1_uptodate = 0;
    }
    clear_bit(ETR_EVENT_UPDATE, &etr_events);
    return eacr;
}

/*
 * Set up a timer that expires after the etr_tolec + 1.6 seconds if
 * one of the ports needs an update.
 */
static void etr_set_tolec_timeout(unsigned long long now)
{
    unsigned long micros;

    if ((!etr_eacr.p0 || etr_port0_uptodate) &&
        (!etr_eacr.p1 || etr_port1_uptodate))
        return;
    micros = (now > etr_tolec) ? ((now - etr_tolec) >> 12) : 0;
    micros = (micros > 1600000) ? 0 : 1600000 - micros;
    mod_timer(&etr_timer, jiffies + (micros * HZ) / 1000000 + 1);
}

/*
 * Set up a time that expires after 1/2 second.
 */
static void etr_set_sync_timeout(void)
{
    mod_timer(&etr_timer, jiffies + HZ/2);
}

/*
 * Update the aib information for one or both ports.
 */
static struct etr_eacr etr_handle_update(struct etr_aib *aib,
                     struct etr_eacr eacr)
{
    /* With both ports disabled the aib information is useless. */
    if (!eacr.e0 && !eacr.e1)
        return eacr;

    /* Update port0 or port1 with aib stored in etr_work_fn. */
    if (aib->esw.q == 0) {
        /* Information for port 0 stored. */
        if (eacr.p0 && !etr_port0_uptodate) {
            etr_port0 = *aib;
            if (etr_port0_online)
                etr_port0_uptodate = 1;
        }
    } else {
        /* Information for port 1 stored. */
        if (eacr.p1 && !etr_port1_uptodate) {
            etr_port1 = *aib;
            if (etr_port0_online)
                etr_port1_uptodate = 1;
        }
    }

    /*
     * Do not try to get the alternate port aib if the clock
     * is not in sync yet.
     */
    if (!eacr.es || !check_sync_clock())
        return eacr;

    /*
     * If steai is available we can get the information about
     * the other port immediately. If only stetr is available the
     * data-port bit toggle has to be used.
     */
    if (etr_steai_available) {
        if (eacr.p0 && !etr_port0_uptodate) {
            etr_steai_cv(&etr_port0, ETR_STEAI_PORT_0);
            etr_port0_uptodate = 1;
        }
        if (eacr.p1 && !etr_port1_uptodate) {
            etr_steai_cv(&etr_port1, ETR_STEAI_PORT_1);
            etr_port1_uptodate = 1;
        }
    } else {
        /*
         * One port was updated above, if the other
         * port is not uptodate toggle dp bit.
         */
        if ((eacr.p0 && !etr_port0_uptodate) ||
            (eacr.p1 && !etr_port1_uptodate))
            eacr.dp ^= 1;
        else
            eacr.dp = 0;
    }
    return eacr;
}

/*
 * Write new etr control register if it differs from the current one.
 * Return 1 if etr_tolec has been updated as well.
 */
static void etr_update_eacr(struct etr_eacr eacr)
{
    int dp_changed;

    if (memcmp(&etr_eacr, &eacr, sizeof(eacr)) == 0)
        /* No change, return. */
        return;
    /*
     * The disable of an active port of the change of the data port
     * bit can/will cause a change in the data port.
     */
    dp_changed = etr_eacr.e0 > eacr.e0 || etr_eacr.e1 > eacr.e1 ||
        (etr_eacr.dp ^ eacr.dp) != 0;
    etr_eacr = eacr;
    etr_setr(&etr_eacr);
    if (dp_changed)
        etr_tolec = get_clock();
}

/*
 * ETR work. In this function you'll find the main logic. In
 * particular this is the only function that calls etr_update_eacr(),
 * it "controls" the etr control register.
 */
static void etr_work_fn(struct work_struct *work)
{
    unsigned long long now;
    struct etr_eacr eacr;
    struct etr_aib aib;
    int sync_port;

    /* prevent multiple execution. */
    mutex_lock(&etr_work_mutex);

    /* Create working copy of etr_eacr. */
    eacr = etr_eacr;

    /* Check for the different events and their immediate effects. */
    eacr = etr_handle_events(eacr);

    /* Check if ETR is supposed to be active. */
    eacr.ea = eacr.p0 || eacr.p1;
    if (!eacr.ea) {
        /* Both ports offline. Reset everything. */
        eacr.dp = eacr.es = eacr.sl = 0;
        on_each_cpu(disable_sync_clock, NULL, 1);
        del_timer_sync(&etr_timer);
        etr_update_eacr(eacr);
        goto out_unlock;
    }

    /* Store aib to get the current ETR status word. */
    BUG_ON(etr_stetr(&aib) != 0);
    etr_port0.esw = etr_port1.esw = aib.esw;    /* Copy status word. */
    now = get_clock();

    /*
     * Update the port information if the last stepping port change
     * or data port change is older than 1.6 seconds.
     */
    if (now >= etr_tolec + (1600000 << 12))
        eacr = etr_handle_update(&aib, eacr);

    /*
     * Select ports to enable. The preferred synchronization mode is PPS.
     * If a port can be enabled depends on a number of things:
     * 1) The port needs to be online and uptodate. A port is not
     *    disabled just because it is not uptodate, but it is only
     *    enabled if it is uptodate.
     * 2) The port needs to have the same mode (pps / etr).
     * 3) The port needs to be usable -> etr_port_valid() == 1
     * 4) To enable the second port the clock needs to be in sync.
     * 5) If both ports are useable and are ETR ports, the network id
     *    has to be the same.
     * The eacr.sl bit is used to indicate etr mode vs. pps mode.
     */
    if (eacr.p0 && aib.esw.psc0 == etr_lpsc_pps_mode) {
        eacr.sl = 0;
        eacr.e0 = 1;
        if (!etr_mode_is_pps(etr_eacr))
            eacr.es = 0;
        if (!eacr.es || !eacr.p1 || aib.esw.psc1 != etr_lpsc_pps_mode)
            eacr.e1 = 0;
        // FIXME: uptodate checks ?
        else if (etr_port0_uptodate && etr_port1_uptodate)
            eacr.e1 = 1;
        sync_port = (etr_port0_uptodate &&
                 etr_port_valid(&etr_port0, 0)) ? 0 : -1;
    } else if (eacr.p1 && aib.esw.psc1 == etr_lpsc_pps_mode) {
        eacr.sl = 0;
        eacr.e0 = 0;
        eacr.e1 = 1;
        if (!etr_mode_is_pps(etr_eacr))
            eacr.es = 0;
        sync_port = (etr_port1_uptodate &&
                 etr_port_valid(&etr_port1, 1)) ? 1 : -1;
    } else if (eacr.p0 && aib.esw.psc0 == etr_lpsc_operational_step) {
        eacr.sl = 1;
        eacr.e0 = 1;
        if (!etr_mode_is_etr(etr_eacr))
            eacr.es = 0;
        if (!eacr.es || !eacr.p1 ||
            aib.esw.psc1 != etr_lpsc_operational_alt)
            eacr.e1 = 0;
        else if (etr_port0_uptodate && etr_port1_uptodate &&
             etr_compare_network(&etr_port0, &etr_port1))
            eacr.e1 = 1;
        sync_port = (etr_port0_uptodate &&
                 etr_port_valid(&etr_port0, 0)) ? 0 : -1;
    } else if (eacr.p1 && aib.esw.psc1 == etr_lpsc_operational_step) {
        eacr.sl = 1;
        eacr.e0 = 0;
        eacr.e1 = 1;
        if (!etr_mode_is_etr(etr_eacr))
            eacr.es = 0;
        sync_port = (etr_port1_uptodate &&
                 etr_port_valid(&etr_port1, 1)) ? 1 : -1;
    } else {
        /* Both ports not usable. */
        eacr.es = eacr.sl = 0;
        sync_port = -1;
    }

    /*
     * If the clock is in sync just update the eacr and return.
     * If there is no valid sync port wait for a port update.
     */
    if ((eacr.es && check_sync_clock()) || sync_port < 0) {
        etr_update_eacr(eacr);
        etr_set_tolec_timeout(now);
        goto out_unlock;
    }

    /*
     * Prepare control register for clock syncing
     * (reset data port bit, set sync check control.
     */
    eacr.dp = 0;
    eacr.es = 1;

    /*
     * Update eacr and try to synchronize the clock. If the update
     * of eacr caused a stepping port switch (or if we have to
     * assume that a stepping port switch has occurred) or the
     * clock syncing failed, reset the sync check control bit
     * and set up a timer to try again after 0.5 seconds
     */
    etr_update_eacr(eacr);
    if (now < etr_tolec + (1600000 << 12) ||
        etr_sync_clock_stop(&aib, sync_port) != 0) {
        /* Sync failed. Try again in 1/2 second. */
        eacr.es = 0;
        etr_update_eacr(eacr);
        etr_set_sync_timeout();
    } else
        etr_set_tolec_timeout(now);
out_unlock:
    mutex_unlock(&etr_work_mutex);
}

/*
 * Sysfs interface functions
 */
static struct bus_type etr_subsys = {
    .name       = "etr",
    .dev_name   = "etr",
};

static struct device etr_port0_dev = {
    .id = 0,
    .bus    = &etr_subsys,
};

static struct device etr_port1_dev = {
    .id = 1,
    .bus    = &etr_subsys,
};

/*
 * ETR subsys attributes
 */
static ssize_t etr_stepping_port_show(struct device *dev,
                    struct device_attribute *attr,
                    char *buf)
{
    return sprintf(buf, "%i\n", etr_port0.esw.p);
}

static DEVICE_ATTR(stepping_port, 0400, etr_stepping_port_show, NULL);

static ssize_t etr_stepping_mode_show(struct device *dev,
                    struct device_attribute *attr,
                    char *buf)
{
    char *mode_str;

    if (etr_mode_is_pps(etr_eacr))
        mode_str = "pps";
    else if (etr_mode_is_etr(etr_eacr))
        mode_str = "etr";
    else
        mode_str = "local";
    return sprintf(buf, "%s\n", mode_str);
}

static DEVICE_ATTR(stepping_mode, 0400, etr_stepping_mode_show, NULL);

/*
 * ETR port attributes
 */
static inline struct etr_aib *etr_aib_from_dev(struct device *dev)
{
    if (dev == &etr_port0_dev)
        return etr_port0_online ? &etr_port0 : NULL;
    else
        return etr_port1_online ? &etr_port1 : NULL;
}

static ssize_t etr_online_show(struct device *dev,
                struct device_attribute *attr,
                char *buf)
{
    unsigned int online;

    online = (dev == &etr_port0_dev) ? etr_port0_online : etr_port1_online;
    return sprintf(buf, "%i\n", online);
}

static ssize_t etr_online_store(struct device *dev,
                struct device_attribute *attr,
                const char *buf, size_t count)
{
    unsigned int value;

    value = simple_strtoul(buf, NULL, 0);
    if (value != 0 && value != 1)
        return -EINVAL;
    if (!test_bit(CLOCK_SYNC_HAS_ETR, &clock_sync_flags))
        return -EOPNOTSUPP;
    mutex_lock(&clock_sync_mutex);
    if (dev == &etr_port0_dev) {
        if (etr_port0_online == value)
            goto out;   /* Nothing to do. */
        etr_port0_online = value;
        if (etr_port0_online && etr_port1_online)
            set_bit(CLOCK_SYNC_ETR, &clock_sync_flags);
        else
            clear_bit(CLOCK_SYNC_ETR, &clock_sync_flags);
        set_bit(ETR_EVENT_PORT0_CHANGE, &etr_events);
        queue_work(time_sync_wq, &etr_work);
    } else {
        if (etr_port1_online == value)
            goto out;   /* Nothing to do. */
        etr_port1_online = value;
        if (etr_port0_online && etr_port1_online)
            set_bit(CLOCK_SYNC_ETR, &clock_sync_flags);
        else
            clear_bit(CLOCK_SYNC_ETR, &clock_sync_flags);
        set_bit(ETR_EVENT_PORT1_CHANGE, &etr_events);
        queue_work(time_sync_wq, &etr_work);
    }
out:
    mutex_unlock(&clock_sync_mutex);
    return count;
}

static DEVICE_ATTR(online, 0600, etr_online_show, etr_online_store);

static ssize_t etr_stepping_control_show(struct device *dev,
                    struct device_attribute *attr,
                    char *buf)
{
    return sprintf(buf, "%i\n", (dev == &etr_port0_dev) ?
               etr_eacr.e0 : etr_eacr.e1);
}

static DEVICE_ATTR(stepping_control, 0400, etr_stepping_control_show, NULL);

static ssize_t etr_mode_code_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
    if (!etr_port0_online && !etr_port1_online)
        /* Status word is not uptodate if both ports are offline. */
        return -ENODATA;
    return sprintf(buf, "%i\n", (dev == &etr_port0_dev) ?
               etr_port0.esw.psc0 : etr_port0.esw.psc1);
}

static DEVICE_ATTR(state_code, 0400, etr_mode_code_show, NULL);

static ssize_t etr_untuned_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
    struct etr_aib *aib = etr_aib_from_dev(dev);

    if (!aib || !aib->slsw.v1)
        return -ENODATA;
    return sprintf(buf, "%i\n", aib->edf1.u);
}

static DEVICE_ATTR(untuned, 0400, etr_untuned_show, NULL);

static ssize_t etr_network_id_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
    struct etr_aib *aib = etr_aib_from_dev(dev);

    if (!aib || !aib->slsw.v1)
        return -ENODATA;
    return sprintf(buf, "%i\n", aib->edf1.net_id);
}

static DEVICE_ATTR(network, 0400, etr_network_id_show, NULL);

static ssize_t etr_id_show(struct device *dev,
            struct device_attribute *attr, char *buf)
{
    struct etr_aib *aib = etr_aib_from_dev(dev);

    if (!aib || !aib->slsw.v1)
        return -ENODATA;
    return sprintf(buf, "%i\n", aib->edf1.etr_id);
}

static DEVICE_ATTR(id, 0400, etr_id_show, NULL);

static ssize_t etr_port_number_show(struct device *dev,
            struct device_attribute *attr, char *buf)
{
    struct etr_aib *aib = etr_aib_from_dev(dev);

    if (!aib || !aib->slsw.v1)
        return -ENODATA;
    return sprintf(buf, "%i\n", aib->edf1.etr_pn);
}

static DEVICE_ATTR(port, 0400, etr_port_number_show, NULL);

static ssize_t etr_coupled_show(struct device *dev,
            struct device_attribute *attr, char *buf)
{
    struct etr_aib *aib = etr_aib_from_dev(dev);

    if (!aib || !aib->slsw.v3)
        return -ENODATA;
    return sprintf(buf, "%i\n", aib->edf3.c);
}

static DEVICE_ATTR(coupled, 0400, etr_coupled_show, NULL);

static ssize_t etr_local_time_show(struct device *dev,
            struct device_attribute *attr, char *buf)
{
    struct etr_aib *aib = etr_aib_from_dev(dev);

    if (!aib || !aib->slsw.v3)
        return -ENODATA;
    return sprintf(buf, "%i\n", aib->edf3.blto);
}

static DEVICE_ATTR(local_time, 0400, etr_local_time_show, NULL);

static ssize_t etr_utc_offset_show(struct device *dev,
            struct device_attribute *attr, char *buf)
{
    struct etr_aib *aib = etr_aib_from_dev(dev);

    if (!aib || !aib->slsw.v3)
        return -ENODATA;
    return sprintf(buf, "%i\n", aib->edf3.buo);
}

static DEVICE_ATTR(utc_offset, 0400, etr_utc_offset_show, NULL);

static struct device_attribute *etr_port_attributes[] = {
    &dev_attr_online,
    &dev_attr_stepping_control,
    &dev_attr_state_code,
    &dev_attr_untuned,
    &dev_attr_network,
    &dev_attr_id,
    &dev_attr_port,
    &dev_attr_coupled,
    &dev_attr_local_time,
    &dev_attr_utc_offset,
    NULL
};

static int __init etr_register_port(struct device *dev)
{
    struct device_attribute **attr;
    int rc;

    rc = device_register(dev);
    if (rc)
        goto out;
    for (attr = etr_port_attributes; *attr; attr++) {
        rc = device_create_file(dev, *attr);
        if (rc)
            goto out_unreg;
    }
    return 0;
out_unreg:
    for (; attr >= etr_port_attributes; attr--)
        device_remove_file(dev, *attr);
    device_unregister(dev);
out:
    return rc;
}

static void __init etr_unregister_port(struct device *dev)
{
    struct device_attribute **attr;

    for (attr = etr_port_attributes; *attr; attr++)
        device_remove_file(dev, *attr);
    device_unregister(dev);
}

static int __init etr_init_sysfs(void)
{
    int rc;

    rc = subsys_system_register(&etr_subsys, NULL);
    if (rc)
        goto out;
    rc = device_create_file(etr_subsys.dev_root, &dev_attr_stepping_port);
    if (rc)
        goto out_unreg_subsys;
    rc = device_create_file(etr_subsys.dev_root, &dev_attr_stepping_mode);
    if (rc)
        goto out_remove_stepping_port;
    rc = etr_register_port(&etr_port0_dev);
    if (rc)
        goto out_remove_stepping_mode;
    rc = etr_register_port(&etr_port1_dev);
    if (rc)
        goto out_remove_port0;
    return 0;

out_remove_port0:
    etr_unregister_port(&etr_port0_dev);
out_remove_stepping_mode:
    device_remove_file(etr_subsys.dev_root, &dev_attr_stepping_mode);
out_remove_stepping_port:
    device_remove_file(etr_subsys.dev_root, &dev_attr_stepping_port);
out_unreg_subsys:
    bus_unregister(&etr_subsys);
out:
    return rc;
}

device_initcall(etr_init_sysfs);

/*
 * Server Time Protocol (STP) code.
 */
static int stp_online;
static struct stp_sstpi stp_info;
static void *stp_page;

static void stp_work_fn(struct work_struct *work);
static DEFINE_MUTEX(stp_work_mutex);
static DECLARE_WORK(stp_work, stp_work_fn);
static struct timer_list stp_timer;

static int __init early_parse_stp(char *p)
{
    if (strncmp(p, "off", 3) == 0)
        stp_online = 0;
    else if (strncmp(p, "on", 2) == 0)
        stp_online = 1;
    return 0;
}
early_param("stp", early_parse_stp);

/*
 * Reset STP attachment.
 */
static void __init stp_reset(void)
{
    int rc;

    stp_page = (void *) get_zeroed_page(GFP_ATOMIC);
    rc = chsc_sstpc(stp_page, STP_OP_CTRL, 0x0000);
    if (rc == 0)
        set_bit(CLOCK_SYNC_HAS_STP, &clock_sync_flags);
    else if (stp_online) {
        pr_warning("The real or virtual hardware system does "
               "not provide an STP interface\n");
        free_page((unsigned long) stp_page);
        stp_page = NULL;
        stp_online = 0;
    }
}

static void stp_timeout(unsigned long dummy)
{
    queue_work(time_sync_wq, &stp_work);
}

static int __init stp_init(void)
{
    if (!test_bit(CLOCK_SYNC_HAS_STP, &clock_sync_flags))
        return 0;
    setup_timer(&stp_timer, stp_timeout, 0UL);
    time_init_wq();
    if (!stp_online)
        return 0;
    queue_work(time_sync_wq, &stp_work);
    return 0;
}

arch_initcall(stp_init);

/*
 * STP timing alert. There are three causes:
 * 1) timing status change
 * 2) link availability change
 * 3) time control parameter change
 * In all three cases we are only interested in the clock source state.
 * If a STP clock source is now available use it.
 */
static void stp_timing_alert(struct stp_irq_parm *intparm)
{
    if (intparm->tsc || intparm->lac || intparm->tcpc)
        queue_work(time_sync_wq, &stp_work);
}

/*
 * STP sync check machine check. This is called when the timing state
 * changes from the synchronized state to the unsynchronized state.
 * After a STP sync check the clock is not in sync. The machine check
 * is broadcasted to all cpus at the same time.
 */
void stp_sync_check(void)
{
    disable_sync_clock(NULL);
    queue_work(time_sync_wq, &stp_work);
}

/*
 * STP island condition machine check. This is called when an attached
 * server  attempts to communicate over an STP link and the servers
 * have matching CTN ids and have a valid stratum-1 configuration
 * but the configurations do not match.
 */
void stp_island_check(void)
{
    disable_sync_clock(NULL);
    queue_work(time_sync_wq, &stp_work);
}


static int stp_sync_clock(void *data)
{
    static int first;
    unsigned long long old_clock, delta;
    struct clock_sync_data *stp_sync;
    int rc;

    stp_sync = data;

    if (xchg(&first, 1) == 1) {
        /* Slave */
        clock_sync_cpu(stp_sync);
        return 0;
    }

    /* Wait until all other cpus entered the sync function. */
    while (atomic_read(&stp_sync->cpus) != 0)
        cpu_relax();

    enable_sync_clock();

    rc = 0;
    if (stp_info.todoff[0] || stp_info.todoff[1] ||
        stp_info.todoff[2] || stp_info.todoff[3] ||
        stp_info.tmd != 2) {
        old_clock = get_clock();
        rc = chsc_sstpc(stp_page, STP_OP_SYNC, 0);
        if (rc == 0) {
            delta = adjust_time(old_clock, get_clock(), 0);
            fixup_clock_comparator(delta);
            rc = chsc_sstpi(stp_page, &stp_info,
                    sizeof(struct stp_sstpi));
            if (rc == 0 && stp_info.tmd != 2)
                rc = -EAGAIN;
        }
    }
    if (rc) {
        disable_sync_clock(NULL);
        stp_sync->in_sync = -EAGAIN;
    } else
        stp_sync->in_sync = 1;
    xchg(&first, 0);
    return 0;
}

/*
 * STP work. Check for the STP state and take over the clock
 * synchronization if the STP clock source is usable.
 */
static void stp_work_fn(struct work_struct *work)
{
    struct clock_sync_data stp_sync;
    int rc;

    /* prevent multiple execution. */
    mutex_lock(&stp_work_mutex);

    if (!stp_online) {
        chsc_sstpc(stp_page, STP_OP_CTRL, 0x0000);
        del_timer_sync(&stp_timer);
        goto out_unlock;
    }

    rc = chsc_sstpc(stp_page, STP_OP_CTRL, 0xb0e0);
    if (rc)
        goto out_unlock;

    rc = chsc_sstpi(stp_page, &stp_info, sizeof(struct stp_sstpi));
    if (rc || stp_info.c == 0)
        goto out_unlock;

    /* Skip synchronization if the clock is already in sync. */
    if (check_sync_clock())
        goto out_unlock;

    memset(&stp_sync, 0, sizeof(stp_sync));
    get_online_cpus();
    atomic_set(&stp_sync.cpus, num_online_cpus() - 1);
    stop_machine(stp_sync_clock, &stp_sync, cpu_online_mask);
    put_online_cpus();

    if (!check_sync_clock())
        /*
         * There is a usable clock but the synchonization failed.
         * Retry after a second.
         */
        mod_timer(&stp_timer, jiffies + HZ);

out_unlock:
    mutex_unlock(&stp_work_mutex);
}

/*
 * STP subsys sysfs interface functions
 */
static struct bus_type stp_subsys = {
    .name       = "stp",
    .dev_name   = "stp",
};

static ssize_t stp_ctn_id_show(struct device *dev,
                struct device_attribute *attr,
                char *buf)
{
    if (!stp_online)
        return -ENODATA;
    return sprintf(buf, "%016llx\n",
               *(unsigned long long *) stp_info.ctnid);
}

static DEVICE_ATTR(ctn_id, 0400, stp_ctn_id_show, NULL);

static ssize_t stp_ctn_type_show(struct device *dev,
                struct device_attribute *attr,
                char *buf)
{
    if (!stp_online)
        return -ENODATA;
    return sprintf(buf, "%i\n", stp_info.ctn);
}

static DEVICE_ATTR(ctn_type, 0400, stp_ctn_type_show, NULL);

static ssize_t stp_dst_offset_show(struct device *dev,
                   struct device_attribute *attr,
                   char *buf)
{
    if (!stp_online || !(stp_info.vbits & 0x2000))
        return -ENODATA;
    return sprintf(buf, "%i\n", (int)(s16) stp_info.dsto);
}

static DEVICE_ATTR(dst_offset, 0400, stp_dst_offset_show, NULL);

static ssize_t stp_leap_seconds_show(struct device *dev,
                    struct device_attribute *attr,
                    char *buf)
{
    if (!stp_online || !(stp_info.vbits & 0x8000))
        return -ENODATA;
    return sprintf(buf, "%i\n", (int)(s16) stp_info.leaps);
}

static DEVICE_ATTR(leap_seconds, 0400, stp_leap_seconds_show, NULL);

static ssize_t stp_stratum_show(struct device *dev,
                struct device_attribute *attr,
                char *buf)
{
    if (!stp_online)
        return -ENODATA;
    return sprintf(buf, "%i\n", (int)(s16) stp_info.stratum);
}

static DEVICE_ATTR(stratum, 0400, stp_stratum_show, NULL);

static ssize_t stp_time_offset_show(struct device *dev,
                struct device_attribute *attr,
                char *buf)
{
    if (!stp_online || !(stp_info.vbits & 0x0800))
        return -ENODATA;
    return sprintf(buf, "%i\n", (int) stp_info.tto);
}

static DEVICE_ATTR(time_offset, 0400, stp_time_offset_show, NULL);

static ssize_t stp_time_zone_offset_show(struct device *dev,
                struct device_attribute *attr,
                char *buf)
{
    if (!stp_online || !(stp_info.vbits & 0x4000))
        return -ENODATA;
    return sprintf(buf, "%i\n", (int)(s16) stp_info.tzo);
}

static DEVICE_ATTR(time_zone_offset, 0400,
             stp_time_zone_offset_show, NULL);

static ssize_t stp_timing_mode_show(struct device *dev,
                struct device_attribute *attr,
                char *buf)
{
    if (!stp_online)
        return -ENODATA;
    return sprintf(buf, "%i\n", stp_info.tmd);
}

static DEVICE_ATTR(timing_mode, 0400, stp_timing_mode_show, NULL);

static ssize_t stp_timing_state_show(struct device *dev,
                struct device_attribute *attr,
                char *buf)
{
    if (!stp_online)
        return -ENODATA;
    return sprintf(buf, "%i\n", stp_info.tst);
}

static DEVICE_ATTR(timing_state, 0400, stp_timing_state_show, NULL);

static ssize_t stp_online_show(struct device *dev,
                struct device_attribute *attr,
                char *buf)
{
    return sprintf(buf, "%i\n", stp_online);
}

static ssize_t stp_online_store(struct device *dev,
                struct device_attribute *attr,
                const char *buf, size_t count)
{
    unsigned int value;

    value = simple_strtoul(buf, NULL, 0);
    if (value != 0 && value != 1)
        return -EINVAL;
    if (!test_bit(CLOCK_SYNC_HAS_STP, &clock_sync_flags))
        return -EOPNOTSUPP;
    mutex_lock(&clock_sync_mutex);
    stp_online = value;
    if (stp_online)
        set_bit(CLOCK_SYNC_STP, &clock_sync_flags);
    else
        clear_bit(CLOCK_SYNC_STP, &clock_sync_flags);
    queue_work(time_sync_wq, &stp_work);
    mutex_unlock(&clock_sync_mutex);
    return count;
}

/*
 * Can't use DEVICE_ATTR because the attribute should be named
 * stp/online but dev_attr_online already exists in this file ..
 */
static struct device_attribute dev_attr_stp_online = {
    .attr = { .name = "online", .mode = 0600 },
    .show   = stp_online_show,
    .store  = stp_online_store,
};

static struct device_attribute *stp_attributes[] = {
    &dev_attr_ctn_id,
    &dev_attr_ctn_type,
    &dev_attr_dst_offset,
    &dev_attr_leap_seconds,
    &dev_attr_stp_online,
    &dev_attr_stratum,
    &dev_attr_time_offset,
    &dev_attr_time_zone_offset,
    &dev_attr_timing_mode,
    &dev_attr_timing_state,
    NULL
};

static int __init stp_init_sysfs(void)
{
    struct device_attribute **attr;
    int rc;

    rc = subsys_system_register(&stp_subsys, NULL);
    if (rc)
        goto out;
    for (attr = stp_attributes; *attr; attr++) {
        rc = device_create_file(stp_subsys.dev_root, *attr);
        if (rc)
            goto out_unreg;
    }
    return 0;
out_unreg:
    for (; attr >= stp_attributes; attr--)
        device_remove_file(stp_subsys.dev_root, *attr);
    bus_unregister(&stp_subsys);
out:
    return rc;
}

device_initcall(stp_init_sysfs);