[S390] ETR support.

This patch adds support for clock synchronization to an external time
reference (ETR). The external time reference sends an oscillator
signal and a synchronization signal every 2^20 microseconds to keep
the TOD clocks of all connected servers in sync. For availability
two ETR units can be connected to a machine. If the clock deviates
for more than the sync-check tolerance all cpus get a machine check
that indicates that the clock is out of sync. For the lovely details
how to get the clock back in sync see the code below.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

5 files changed, 1160 insertions, 86 deletions

diff --git a/arch/s390/kernel/s390_ext.c b/arch/s390/kernel/s390_ext.c
index bc5beaa8f98e..acf93dba7727 100644
--- a/arch/s390/kernel/s390_ext.c
+++ b/arch/s390/kernel/s390_ext.c
@@ -125,14 +125,12 @@ void do_extint(struct pt_regs *regs, unsigned short code)
                  * Make sure that the i/o interrupt did not "overtake"
                  * the last HZ timer interrupt.
                  */
-                account_ticks();
+                account_ticks(S390_lowcore.int_clock);
         kstat_cpu(smp_processor_id()).irqs[EXTERNAL_INTERRUPT]++;
         index = ext_hash(code);
         for (p = ext_int_hash[index]; p; p = p->next) {
-                if (likely(p->code == code)) {
-                        if (likely(p->handler))
-                                p->handler(code);
-                }
+                if (likely(p->code == code))
+                        p->handler(code);
         }
         irq_exit();
         set_irq_regs(old_regs);
diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index cb155d9fd749..08f9a4dfb18b 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -457,9 +457,10 @@ int __devinit start_secondary(void *cpuvoid)
         /* Setup the cpu */
         cpu_init();
         preempt_disable();
-        /* init per CPU timer */
+        /* Enable TOD clock interrupts on the secondary cpu. */
         init_cpu_timer();
 #ifdef CONFIG_VIRT_TIMER
+        /* Enable cpu timer interrupts on the secondary cpu. */
         init_cpu_vtimer();
 #endif
         /* Enable pfault pseudo page faults on this cpu. */
diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index 5d4a190fa307..39a72d3cb89a 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -37,11 +37,15 @@
 #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.
@@ -51,6 +55,7 @@
 #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;
@@ -89,29 +94,21 @@ void tod_to_timeval(__u64 todval, struct timespec *xtime)
 #define s390_do_profile()       do { ; } while(0)
 #endif /* CONFIG_PROFILING */
 
-
 /*
- * timer_interrupt() needs to keep up the real-time clock,
- * as well as call the "do_timer()" routine every clocktick
+ * 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(void)
+void account_ticks(u64 time)
 {
-        __u64 tmp;
         __u32 ticks;
+        __u64 tmp;
 
         /* Calculate how many ticks have passed. */
-        if (S390_lowcore.int_clock < S390_lowcore.jiffy_timer) {
-                /*
-                 * We have to program the clock comparator even if
-                 * no tick has passed. That happens if e.g. an i/o
-                 * interrupt wakes up an idle processor that has
-                 * switched off its hz timer.
-                 */
-                tmp = S390_lowcore.jiffy_timer + CPU_DEVIATION;
-                asm volatile ("SCKC %0" : : "m" (tmp));
+        if (time < S390_lowcore.jiffy_timer)
                 return;
-        }
-        tmp = S390_lowcore.int_clock - S390_lowcore.jiffy_timer;
+        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 +=
@@ -124,10 +121,6 @@ void account_ticks(void)
                 S390_lowcore.jiffy_timer += CLK_TICKS_PER_JIFFY;
         }
 
-        /* set clock comparator for next tick */
-        tmp = S390_lowcore.jiffy_timer + CPU_DEVIATION;
-        asm volatile ("SCKC %0" : : "m" (tmp));
-
 #ifdef CONFIG_SMP
         /*
          * Do not rely on the boot cpu to do the calls to do_timer.
@@ -210,7 +203,7 @@ static inline void stop_hz_timer(void)
                 if (timer >= jiffies_timer_cc)
                         todval = timer;
         }
-        asm volatile ("SCKC %0" : : "m" (todval));
+        set_clock_comparator(todval);
 }
 
 /*
@@ -223,7 +216,8 @@ static inline void start_hz_timer(void)
 
         if (!cpu_isset(smp_processor_id(), nohz_cpu_mask))
                 return;
-        account_ticks();
+        account_ticks(get_clock());
+        set_clock_comparator(S390_lowcore.jiffy_timer + CPU_DEVIATION);
         cpu_clear(smp_processor_id(), nohz_cpu_mask);
 }
 
@@ -254,21 +248,56 @@ static void __init nohz_init(void)
 #endif
 
 /*
- * Start the clock comparator on the current CPU.
+ * 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)
 {
-        unsigned long cr0;
-        __u64 timer;
+        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.");
 
-        timer = jiffies_timer_cc + jiffies_64 * CLK_TICKS_PER_JIFFY;
-        S390_lowcore.jiffy_timer = timer + CLK_TICKS_PER_JIFFY;
-        timer += CLK_TICKS_PER_JIFFY + CPU_DEVIATION;
-        asm volatile ("SCKC %0" : : "m" (timer));
-        /* allow clock comparator timer interrupt */
-        __ctl_store(cr0, 0, 0);
-        cr0 |= 0x800;
-        __ctl_load(cr0, 0, 0);
+        return TOD_UNIX_EPOCH;
 }
 
 static cycle_t read_tod_clock(void)
@@ -293,48 +322,31 @@ static struct clocksource clocksource_tod = {
  */
 void __init time_init(void)
 {
-        __u64 set_time_cc;
-        int cc;
-
-        /* kick the TOD clock */
-        asm volatile(
-                "       stck    0(%2)\n"
-                "       ipm     %0\n"
-                "       srl     %0,28"
-                : "=d" (cc), "=m" (init_timer_cc)
-                : "a" (&init_timer_cc) : "cc");
-        switch (cc) {
-        case 0: /* clock in set state: all is fine */
-                break;
-        case 1: /* clock in non-set state: FIXME */
-                printk("time_init: TOD clock in non-set state\n");
-                break;
-        case 2: /* clock in error state: FIXME */
-                printk("time_init: TOD clock in error state\n");
-                break;
-        case 3: /* clock in stopped or not-operational state: FIXME */
-                printk("time_init: TOD clock stopped/non-operational\n");
-                break;
-        }
+        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 */
-        xtime_cc = init_timer_cc + CLK_TICKS_PER_JIFFY;
-        set_time_cc = init_timer_cc - 0x8126d60e46000000LL +
-                (0x3c26700LL*1000000*4096);
-        tod_to_timeval(set_time_cc, &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, NULL,
+        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");
 
-        init_cpu_timer();
+        /* 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();
@@ -343,5 +355,1048 @@ void __init time_init(void)
 #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);
diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c
index 01f3d29bdb06..9d5b02801b46 100644
--- a/arch/s390/kernel/vtime.c
+++ b/arch/s390/kernel/vtime.c
@@ -524,16 +524,15 @@ EXPORT_SYMBOL(del_virt_timer);
 void init_cpu_vtimer(void)
 {
         struct vtimer_queue *vt_list;
-        unsigned long cr0;
 
         /* kick the virtual timer */
         S390_lowcore.exit_timer = VTIMER_MAX_SLICE;
         S390_lowcore.last_update_timer = VTIMER_MAX_SLICE;
         asm volatile ("SPT %0" : : "m" (S390_lowcore.last_update_timer));
         asm volatile ("STCK %0" : "=m" (S390_lowcore.last_update_clock));
-        __ctl_store(cr0, 0, 0);
-        cr0 |= 0x400;
-        __ctl_load(cr0, 0, 0);
+
+        /* enable cpu timer interrupts */
+        __ctl_set_bit(0,10);
 
         vt_list = &per_cpu(virt_cpu_timer, smp_processor_id());
         INIT_LIST_HEAD(&vt_list->list);
@@ -572,6 +571,7 @@ void __init vtime_init(void)
         if (register_idle_notifier(&vtimer_idle_nb))
                 panic("Couldn't register idle notifier");
 
+        /* Enable cpu timer interrupts on the boot cpu. */
         init_cpu_vtimer();
 }
 
diff --git a/arch/s390/lib/delay.c b/arch/s390/lib/delay.c
index 027c4742a001..02854449b74b 100644
--- a/arch/s390/lib/delay.c
+++ b/arch/s390/lib/delay.c
@@ -1,5 +1,5 @@
 /*
- *  arch/s390/kernel/delay.c
+ *  arch/s390/lib/delay.c
  *    Precise Delay Loops for S390
  *
  *  S390 version
@@ -13,10 +13,8 @@
 
 #include <linux/sched.h>
 #include <linux/delay.h>
-
-#ifdef CONFIG_SMP
-#include <asm/smp.h>
-#endif
+#include <linux/timex.h>
+#include <linux/irqflags.h>
 
 void __delay(unsigned long loops)
 {
@@ -31,17 +29,39 @@ void __delay(unsigned long loops)
 }
 
 /*
- * Waits for 'usecs' microseconds using the tod clock, giving up the time slice
- * of the virtual PU inbetween to avoid congestion.
+ * Waits for 'usecs' microseconds using the TOD clock comparator.
  */
 void __udelay(unsigned long usecs)
 {
-        uint64_t start_cc;
+        u64 end, time, jiffy_timer = 0;
+        unsigned long flags, cr0, mask, dummy;
+
+        local_irq_save(flags);
+        if (raw_irqs_disabled_flags(flags)) {
+                jiffy_timer = S390_lowcore.jiffy_timer;
+                S390_lowcore.jiffy_timer = -1ULL - (4096 << 12);
+                __ctl_store(cr0, 0, 0);
+                dummy = (cr0 & 0xffff00e0) | 0x00000800;
+                __ctl_load(dummy , 0, 0);
+                mask = psw_kernel_bits | PSW_MASK_WAIT | PSW_MASK_EXT;
+        } else
+                mask = psw_kernel_bits | PSW_MASK_WAIT |
+                        PSW_MASK_EXT | PSW_MASK_IO;
+
+        end = get_clock() + ((u64) usecs << 12);
+        do {
+                time = end < S390_lowcore.jiffy_timer ?
+                        end : S390_lowcore.jiffy_timer;
+                set_clock_comparator(time);
+                trace_hardirqs_on();
+                __load_psw_mask(mask);
+                local_irq_disable();
+        } while (get_clock() < end);
 
-        if (usecs == 0)
-                return;
-        start_cc = get_clock();
-        do {
-                cpu_relax();
-        } while (((get_clock() - start_cc)/4096) < usecs);
+        if (raw_irqs_disabled_flags(flags)) {
+                __ctl_load(cr0, 0, 0);
+                S390_lowcore.jiffy_timer = jiffy_timer;
+        }
+        set_clock_comparator(S390_lowcore.jiffy_timer);
+        local_irq_restore(flags);
 }