[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, 34 insertions, 14 deletions

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);
 }