arch/s390/kernel/time.c

/*
 *  arch/s390/kernel/time.c
 *    Time of day based timer functions.
 *
 *  S390 version
 *    Copyright (C) 1999 IBM Deutschland Entwicklung GmbH, IBM Corporation
 *    Author(s): Hartmut Penner (hp@de.ibm.com),
 *               Martin Schwidefsky (schwidefsky@de.ibm.com),
 *               Denis Joseph Barrow (djbarrow@de.ibm.com,barrow_dj@yahoo.com)
 *
 *  Derived from "arch/i386/kernel/time.c"
 *    Copyright (C) 1991, 1992, 1995  Linus Torvalds
 */

#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/time.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/clocksource.h>

#include <asm/uaccess.h>
#include <asm/delay.h>
#include <asm/s390_ext.h>
#include <asm/div64.h>
#include <asm/irq.h>
#include <asm/irq_regs.h>
#include <asm/timer.h>
#include <asm/etr.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)

/* The value of the TOD clock for 1.1.1970. */
#define TOD_UNIX_EPOCH 0x7d91048bca000000ULL

/*
 * Create a small time difference between the timer interrupts
 * on the different cpus to avoid lock contention.
 */
#define CPU_DEVIATION       (smp_processor_id() << 12)

#define TICK_SIZE tick

static ext_int_info_t ext_int_info_cc;
static ext_int_info_t ext_int_etr_cc;
static u64 init_timer_cc;
static u64 jiffies_timer_cc;
static u64 xtime_cc;

/*
 * Scheduler clock - returns current time in nanosec units.
 */
unsigned long long sched_clock(void)
{
	return ((get_clock() - jiffies_timer_cc) * 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 *xtime)
{
	unsigned long long sec;

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

#ifdef CONFIG_PROFILING
#define s390_do_profile()	profile_tick(CPU_PROFILING)
#else
#define s390_do_profile()	do { ; } while(0)
#endif /* CONFIG_PROFILING */

/*
 * Advance the per cpu tick counter up to the time given with the
 * "time" argument. The per cpu update consists of accounting
 * the virtual cpu time, calling update_process_times and calling
 * the profiling hook. If xtime is before time it is advanced as well.
 */
void account_ticks(u64 time)
{
	__u32 ticks;
	__u64 tmp;

	/* Calculate how many ticks have passed. */
	if (time < S390_lowcore.jiffy_timer)
		return;
	tmp = time - S390_lowcore.jiffy_timer;
	if (tmp >= 2*CLK_TICKS_PER_JIFFY) {  /* more than two ticks ? */
		ticks = __div(tmp, CLK_TICKS_PER_JIFFY) + 1;
		S390_lowcore.jiffy_timer +=
			CLK_TICKS_PER_JIFFY * (__u64) ticks;
	} else if (tmp >= CLK_TICKS_PER_JIFFY) {
		ticks = 2;
		S390_lowcore.jiffy_timer += 2*CLK_TICKS_PER_JIFFY;
	} else {
		ticks = 1;
		S390_lowcore.jiffy_timer += CLK_TICKS_PER_JIFFY;
	}

#ifdef CONFIG_SMP
	/*
	 * Do not rely on the boot cpu to do the calls to do_timer.
	 * Spread it over all cpus instead.
	 */
	write_seqlock(&xtime_lock);
	if (S390_lowcore.jiffy_timer > xtime_cc) {
		__u32 xticks;
		tmp = S390_lowcore.jiffy_timer - xtime_cc;
		if (tmp >= 2*CLK_TICKS_PER_JIFFY) {
			xticks = __div(tmp, CLK_TICKS_PER_JIFFY);
			xtime_cc += (__u64) xticks * CLK_TICKS_PER_JIFFY;
		} else {
			xticks = 1;
			xtime_cc += CLK_TICKS_PER_JIFFY;
		}
		do_timer(xticks);
	}
	write_sequnlock(&xtime_lock);
#else
	do_timer(ticks);
#endif

#ifdef CONFIG_VIRT_CPU_ACCOUNTING
	account_tick_vtime(current);
#else
	while (ticks--)
		update_process_times(user_mode(get_irq_regs()));
#endif

	s390_do_profile();
}

#ifdef CONFIG_NO_IDLE_HZ

#ifdef CONFIG_NO_IDLE_HZ_INIT
int sysctl_hz_timer = 0;
#else
int sysctl_hz_timer = 1;
#endif

/*
 * Stop the HZ tick on the current CPU.
 * Only cpu_idle may call this function.
 */
static void stop_hz_timer(void)
{
	unsigned long flags;
	unsigned long seq, next;
	__u64 timer, todval;
	int cpu = smp_processor_id();

	if (sysctl_hz_timer != 0)
		return;

	cpu_set(cpu, nohz_cpu_mask);

	/*
	 * Leave the clock comparator set up for the next timer
	 * tick if either rcu or a softirq is pending.
	 */
	if (rcu_needs_cpu(cpu) || local_softirq_pending()) {
		cpu_clear(cpu, nohz_cpu_mask);
		return;
	}

	/*
	 * This cpu is going really idle. Set up the clock comparator
	 * for the next event.
	 */
	next = next_timer_interrupt();
	do {
		seq = read_seqbegin_irqsave(&xtime_lock, flags);
		timer = ((__u64) next) - ((__u64) jiffies) + jiffies_64;
	} while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
	todval = -1ULL;
	/* Be careful about overflows. */
	if (timer < (-1ULL / CLK_TICKS_PER_JIFFY)) {
		timer = jiffies_timer_cc + timer * CLK_TICKS_PER_JIFFY;
		if (timer >= jiffies_timer_cc)
			todval = timer;
	}
	set_clock_comparator(todval);
}

/*
 * Start the HZ tick on the current CPU.
 * Only cpu_idle may call this function.
 */
static void start_hz_timer(void)
{
	BUG_ON(!in_interrupt());

	if (!cpu_isset(smp_processor_id(), nohz_cpu_mask))
		return;
	account_ticks(get_clock());
	set_clock_comparator(S390_lowcore.jiffy_timer + CPU_DEVIATION);
	cpu_clear(smp_processor_id(), nohz_cpu_mask);
}

static int nohz_idle_notify(struct notifier_block *self,
			    unsigned long action, void *hcpu)
{
	switch (action) {
	case CPU_IDLE:
		stop_hz_timer();
		break;
	case CPU_NOT_IDLE:
		start_hz_timer();
		break;
	}
	return NOTIFY_OK;
}

static struct notifier_block nohz_idle_nb = {
	.notifier_call = nohz_idle_notify,
};

static void __init nohz_init(void)
{
	if (register_idle_notifier(&nohz_idle_nb))
		panic("Couldn't register idle notifier");
}

#endif

/*
 * Set up per cpu jiffy timer and set the clock comparator.
 */
static void setup_jiffy_timer(void)
{
	/* Set up clock comparator to next jiffy. */
	S390_lowcore.jiffy_timer =
		jiffies_timer_cc + (jiffies_64 + 1) * CLK_TICKS_PER_JIFFY;
	set_clock_comparator(S390_lowcore.jiffy_timer + CPU_DEVIATION);
}

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

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

	/* Always allow ETR external interrupts, even without an ETR. */
	__ctl_set_bit(0, 4);
}

static void clock_comparator_interrupt(__u16 code)
{
	/* set clock comparator for next tick */
	set_clock_comparator(S390_lowcore.jiffy_timer + CPU_DEVIATION);
}

static void etr_reset(void);
static void etr_init(void);
static void etr_ext_handler(__u16);

/*
 * Get the TOD clock running.
 */
static u64 __init reset_tod_clock(void)
{
	u64 time;

	etr_reset();
	if (store_clock(&time) == 0)
		return time;
	/* TOD clock not running. Set the clock to Unix Epoch. */
	if (set_clock(TOD_UNIX_EPOCH) != 0 || store_clock(&time) != 0)
		panic("TOD clock not operational.");

	return TOD_UNIX_EPOCH;
}

static cycle_t read_tod_clock(void)
{
	return get_clock();
}

static struct clocksource clocksource_tod = {
	.name		= "tod",
	.rating		= 100,
	.read		= read_tod_clock,
	.mask		= -1ULL,
	.mult		= 1000,
	.shift		= 12,
	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
};


/*
 * Initialize the TOD clock and the CPU timer of
 * the boot cpu.
 */
void __init time_init(void)
{
	init_timer_cc = reset_tod_clock();
	xtime_cc = init_timer_cc + CLK_TICKS_PER_JIFFY;
	jiffies_timer_cc = init_timer_cc - jiffies_64 * CLK_TICKS_PER_JIFFY;

	/* set xtime */
	tod_to_timeval(init_timer_cc - TOD_UNIX_EPOCH, &xtime);
        set_normalized_timespec(&wall_to_monotonic,
                                -xtime.tv_sec, -xtime.tv_nsec);

	/* request the clock comparator external interrupt */
	if (register_early_external_interrupt(0x1004,
					      clock_comparator_interrupt,
					      &ext_int_info_cc) != 0)
                panic("Couldn't request external interrupt 0x1004");

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

	/* request the etr external interrupt */
	if (register_early_external_interrupt(0x1406, etr_ext_handler,
					      &ext_int_etr_cc) != 0)
		panic("Couldn't request external interrupt 0x1406");

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

#ifdef CONFIG_NO_IDLE_HZ
	nohz_init();
#endif

#ifdef CONFIG_VIRT_TIMER
	vtime_init();
#endif
	etr_init();
}

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

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,
};

enum etr_flags {
	ETR_FLAG_ENOSYS,
	ETR_FLAG_EACCES,
	ETR_FLAG_STEAI,
};

/*
 * 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 unsigned long etr_flags;
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 struct tasklet_struct etr_tasklet;
static DEFINE_PER_CPU(atomic_t, etr_sync_word);

static void etr_timeout(unsigned long dummy);
static void etr_tasklet_fn(unsigned long dummy);

/*
 * The etr 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
 * -ENOSYS and -EAGAIN if the clock is not in sync with the external
 * reference. This function is what ETR is all about..
 */
int get_sync_clock(unsigned long long *clock)
{
	atomic_t *sw_ptr;
	unsigned int sw0, sw1;

	sw_ptr = &get_cpu_var(etr_sync_word);
	sw0 = atomic_read(sw_ptr);
	*clock = get_clock();
	sw1 = atomic_read(sw_ptr);
	put_cpu_var(etr_sync_sync);
	if (sw0 == sw1 && (sw0 & 0x80000000U))
		/* Success: time is in sync. */
		return 0;
	if (test_bit(ETR_FLAG_ENOSYS, &etr_flags))
		return -ENOSYS;
	if (test_bit(ETR_FLAG_EACCES, &etr_flags))
		return -EACCES;
	return -EAGAIN;
}
EXPORT_SYMBOL(get_sync_clock);

/*
 * Make get_sync_clock return -EAGAIN.
 */
static void etr_disable_sync_clock(void *dummy)
{
	atomic_t *sw_ptr = &__get_cpu_var(etr_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 etr_enable_sync_clock(void)
{
	atomic_t *sw_ptr = &__get_cpu_var(etr_sync_word);
	atomic_set_mask(0x80000000, sw_ptr);
}

/*
 * 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();
	else {
		set_bit(ETR_FLAG_ENOSYS, &etr_flags);
		if (etr_port0_online || etr_port1_online) {
			printk(KERN_WARNING "Running on non ETR capable "
			       "machine, only local mode available.\n");
			etr_port0_online = etr_port1_online = 0;
		}
	}
}

static void etr_init(void)
{
	struct etr_aib aib;

	if (test_bit(ETR_FLAG_ENOSYS, &etr_flags))
		return;
	/* Check if this machine has the steai instruction. */
	if (etr_steai(&aib, ETR_STEAI_STEPPING_PORT) == 0)
		set_bit(ETR_FLAG_STEAI, &etr_flags);
	setup_timer(&etr_timer, etr_timeout, 0UL);
	tasklet_init(&etr_tasklet, etr_tasklet_fn, 0);
	if (!etr_port0_online && !etr_port1_online)
		set_bit(ETR_FLAG_EACCES, &etr_flags);
	if (etr_port0_online) {
		set_bit(ETR_EVENT_PORT0_CHANGE, &etr_events);
		tasklet_hi_schedule(&etr_tasklet);
	}
	if (etr_port1_online) {
		set_bit(ETR_EVENT_PORT1_CHANGE, &etr_events);
		tasklet_hi_schedule(&etr_tasklet);
	}
}

/*
 * 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;
	etr_disable_sync_clock(NULL);
	set_bit(ETR_EVENT_SWITCH_LOCAL, &etr_events);
	tasklet_hi_schedule(&etr_tasklet);
}

/*
 * 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;
	etr_disable_sync_clock(NULL);
	set_bit(ETR_EVENT_SYNC_CHECK, &etr_events);
	tasklet_hi_schedule(&etr_tasklet);
}

/*
 * ETR external interrupt. 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_ext_handler(__u16 code)
{
	struct etr_interruption_parameter *intparm =
		(struct etr_interruption_parameter *) &S390_lowcore.ext_params;

	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);
	tasklet_hi_schedule(&etr_tasklet);
}

static void etr_timeout(unsigned long dummy)
{
	set_bit(ETR_EVENT_UPDATE, &etr_events);
	tasklet_hi_schedule(&etr_tasklet);
}

/*
 * 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;
}

/*
 * The time is "clock". xtime 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 void etr_adjust_time(unsigned long long clock, unsigned long long delay)
{
	unsigned long long delta, ticks;
	struct timex adjust;

	/*
	 * We don't have to take the xtime lock because the cpu
	 * executing etr_adjust_time is running disabled in
	 * tasklet context and all other cpus are looping in
	 * etr_sync_cpu_start.
	 */
	if (clock > xtime_cc) {
		/* It is later than we thought. */
		delta = ticks = clock - xtime_cc;
		delta = ticks = (delta < delay) ? 0 : delta - delay;
		delta -= do_div(ticks, CLK_TICKS_PER_JIFFY);
		init_timer_cc = init_timer_cc + delta;
		jiffies_timer_cc = jiffies_timer_cc + delta;
		xtime_cc = xtime_cc + delta;
		adjust.offset = ticks * (1000000 / HZ);
	} else {
		/* It is earlier than we thought. */
		delta = ticks = xtime_cc - clock;
		delta -= do_div(ticks, CLK_TICKS_PER_JIFFY);
		init_timer_cc = init_timer_cc - delta;
		jiffies_timer_cc = jiffies_timer_cc - delta;
		xtime_cc = xtime_cc - delta;
		adjust.offset = -ticks * (1000000 / HZ);
	}
	if (adjust.offset != 0) {
		printk(KERN_NOTICE "etr: time adjusted by %li micro-seconds\n",
		       adjust.offset);
		adjust.modes = ADJ_OFFSET_SINGLESHOT;
		do_adjtimex(&adjust);
	}
}

static void etr_sync_cpu_start(void *dummy)
{
	int *in_sync = dummy;

	etr_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 (*in_sync == 0)
		__udelay(1);
	if (*in_sync != 1)
		/* Didn't work. Clear per-cpu in sync bit again. */
		etr_disable_sync_clock(NULL);
	/*
	 * This round of TOD syncing is done. Set the clock comparator
	 * to the next tick and let the processor continue.
	 */
	setup_jiffy_timer();
}

static void etr_sync_cpu_end(void *dummy)
{
}

/*
 * Sync the TOD clock using the port refered 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(struct etr_aib *aib, int port)
{
	struct etr_aib *sync_port;
	unsigned long long clock, delay;
	int in_sync, 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;

	/*
	 * Catch all other cpus and make them wait until we have
	 * successfully synced the clock. smp_call_function will
	 * return after all other cpus are in etr_sync_cpu_start.
	 */
	in_sync = 0;
	preempt_disable();
	smp_call_function(etr_sync_cpu_start,&in_sync,0,0);
	local_irq_disable();
	etr_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;
	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;
		etr_adjust_time(clock, delay);
		setup_jiffy_timer();
		/* Verify that the clock is properly set. */
		if (!etr_aib_follows(sync_port, aib, port)) {
			/* Didn't work. */
			etr_disable_sync_clock(NULL);
			in_sync = -EAGAIN;
			rc = -EAGAIN;
		} else {
			in_sync = 1;
			rc = 0;
		}
	} else {
		/* Could not set the clock ?!? */
		__ctl_clear_bit(0, 29);
		__ctl_clear_bit(14, 21);
		etr_disable_sync_clock(NULL);
		in_sync = -EAGAIN;
		rc = -EAGAIN;
	}
	local_irq_enable();
	smp_call_function(etr_sync_cpu_end,NULL,0,0);
	preempt_enable();
	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_tasklet_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)
		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 (test_bit(ETR_FLAG_STEAI, &etr_flags)) {
		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 tasklet. 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_tasklet_fn(unsigned long dummy)
{
	unsigned long long now;
	struct etr_eacr eacr;
	struct etr_aib aib;
	int sync_port;

	/* 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(etr_disable_sync_clock, NULL, 0, 1);
		del_timer_sync(&etr_timer);
		etr_update_eacr(eacr);
		set_bit(ETR_FLAG_EACCES, &etr_flags);
		return;
	}

	/* 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 prefered 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;
		clear_bit(ETR_FLAG_EACCES, &etr_flags);
	} 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;
		clear_bit(ETR_FLAG_EACCES, &etr_flags);
	} 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;
		clear_bit(ETR_FLAG_EACCES, &etr_flags);
	} 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;
		clear_bit(ETR_FLAG_EACCES, &etr_flags);
	} else {
		/* Both ports not usable. */
		eacr.es = eacr.sl = 0;
		sync_port = -1;
		set_bit(ETR_FLAG_EACCES, &etr_flags);
	}

	/*
	 * 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 || sync_port < 0) {
		etr_update_eacr(eacr);
		etr_set_tolec_timeout(now);
		return;
	}

	/*
	 * 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 occured) 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(&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);
}

/*
 * Sysfs interface functions
 */
static struct sysdev_class etr_sysclass = {
	set_kset_name("etr")
};

static struct sys_device etr_port0_dev = {
	.id	= 0,
	.cls	= &etr_sysclass,
};

static struct sys_device etr_port1_dev = {
	.id	= 1,
	.cls	= &etr_sysclass,
};

/*
 * ETR class attributes
 */
static ssize_t etr_stepping_port_show(struct sysdev_class *class, char *buf)
{
	return sprintf(buf, "%i\n", etr_port0.esw.p);
}

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

static ssize_t etr_stepping_mode_show(struct sysdev_class *class, 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 SYSDEV_CLASS_ATTR(stepping_mode, 0400, etr_stepping_mode_show, NULL);

/*
 * ETR port attributes
 */
static inline struct etr_aib *etr_aib_from_dev(struct sys_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 sys_device *dev, 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 sys_device *dev,
			      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(ETR_FLAG_ENOSYS, &etr_flags))
		return -ENOSYS;
	if (dev == &etr_port0_dev) {
		if (etr_port0_online == value)
			return count;	/* Nothing to do. */
		etr_port0_online = value;
		set_bit(ETR_EVENT_PORT0_CHANGE, &etr_events);
		tasklet_hi_schedule(&etr_tasklet);
	} else {
		if (etr_port1_online == value)
			return count;	/* Nothing to do. */
		etr_port1_online = value;
		set_bit(ETR_EVENT_PORT1_CHANGE, &etr_events);
		tasklet_hi_schedule(&etr_tasklet);
	}
	return count;
}

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

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

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

static ssize_t etr_mode_code_show(struct sys_device *dev, 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 SYSDEV_ATTR(state_code, 0400, etr_mode_code_show, NULL);

static ssize_t etr_untuned_show(struct sys_device *dev, 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 SYSDEV_ATTR(untuned, 0400, etr_untuned_show, NULL);

static ssize_t etr_network_id_show(struct sys_device *dev, 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 SYSDEV_ATTR(network, 0400, etr_network_id_show, NULL);

static ssize_t etr_id_show(struct sys_device *dev, 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 SYSDEV_ATTR(id, 0400, etr_id_show, NULL);

static ssize_t etr_port_number_show(struct sys_device *dev, 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 SYSDEV_ATTR(port, 0400, etr_port_number_show, NULL);

static ssize_t etr_coupled_show(struct sys_device *dev, 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 SYSDEV_ATTR(coupled, 0400, etr_coupled_show, NULL);

static ssize_t etr_local_time_show(struct sys_device *dev, 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 SYSDEV_ATTR(local_time, 0400, etr_local_time_show, NULL);

static ssize_t etr_utc_offset_show(struct sys_device *dev, 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 SYSDEV_ATTR(utc_offset, 0400, etr_utc_offset_show, NULL);

static struct sysdev_attribute *etr_port_attributes[] = {
	&attr_online,
	&attr_stepping_control,
	&attr_state_code,
	&attr_untuned,
	&attr_network,
	&attr_id,
	&attr_port,
	&attr_coupled,
	&attr_local_time,
	&attr_utc_offset,
	NULL
};

static int __init etr_register_port(struct sys_device *dev)
{
	struct sysdev_attribute **attr;
	int rc;

	rc = sysdev_register(dev);
	if (rc)
		goto out;
	for (attr = etr_port_attributes; *attr; attr++) {
		rc = sysdev_create_file(dev, *attr);
		if (rc)
			goto out_unreg;
	}
	return 0;
out_unreg:
	for (; attr >= etr_port_attributes; attr--)
		sysdev_remove_file(dev, *attr);
	sysdev_unregister(dev);
out:
	return rc;
}

static void __init etr_unregister_port(struct sys_device *dev)
{
	struct sysdev_attribute **attr;

	for (attr = etr_port_attributes; *attr; attr++)
		sysdev_remove_file(dev, *attr);
	sysdev_unregister(dev);
}

static int __init etr_init_sysfs(void)
{
	int rc;

	rc = sysdev_class_register(&etr_sysclass);
	if (rc)
		goto out;
	rc = sysdev_class_create_file(&etr_sysclass, &attr_stepping_port);
	if (rc)
		goto out_unreg_class;
	rc = sysdev_class_create_file(&etr_sysclass, &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:
	sysdev_class_remove_file(&etr_sysclass, &attr_stepping_mode);
out_remove_stepping_port:
	sysdev_class_remove_file(&etr_sysclass, &attr_stepping_port);
out_unreg_class:
	sysdev_class_unregister(&etr_sysclass);
out:
	return rc;
}

device_initcall(etr_init_sysfs);