[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, 15 insertions, 2 deletions

diff --git a/drivers/s390/cio/cio.c b/drivers/s390/cio/cio.c
index 07a4cbfc2436..ad2b37929848 100644
--- a/drivers/s390/cio/cio.c
+++ b/drivers/s390/cio/cio.c
@@ -646,7 +646,7 @@ do_IRQ (struct pt_regs *regs)
                  * 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 @@ __disable_subchannel_easy(struct subchannel_id schid, struct schib *schib)
         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 @@ __clear_subchannel_easy(struct subchannel_id schid)
                         if (schid_equal(&ti.schid, &schid))
                                 return 0;
                 }
-                udelay(100);
+                udelay_reset(100);
         }
         return -EBUSY;
 }