[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>
diff --git a/drivers/s390/cio/cio.c b/drivers/s390/cio/cio.c
index 07a4cbf..ad2b379 100644
--- a/drivers/s390/cio/cio.c
+++ b/drivers/s390/cio/cio.c
@@ -646,7 +646,7 @@
* Make sure that the i/o interrupt did not "overtake"
* the last HZ timer interrupt.
*/
- account_ticks();
+ account_ticks(S390_lowcore.int_clock);
/*
* Get interrupt information from lowcore
*/
@@ -850,6 +850,19 @@
return -EBUSY; /* uhm... */
}
+/* we can't use the normal udelay here, since it enables external interrupts */
+
+static void udelay_reset(unsigned long usecs)
+{
+ uint64_t start_cc, end_cc;
+
+ asm volatile ("STCK %0" : "=m" (start_cc));
+ do {
+ cpu_relax();
+ asm volatile ("STCK %0" : "=m" (end_cc));
+ } while (((end_cc - start_cc)/4096) < usecs);
+}
+
static inline int
__clear_subchannel_easy(struct subchannel_id schid)
{
@@ -865,7 +878,7 @@
if (schid_equal(&ti.schid, &schid))
return 0;
}
- udelay(100);
+ udelay_reset(100);
}
return -EBUSY;
}