[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>

1 files changed, 4 insertions, 4 deletions

diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c
index 01f3d29bdb0..9d5b02801b4 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();
 }