s390/debug: make debug event time stamps relative to the boot TOD clock

The debug features currently uses absolute TOD time stamps for the
debug events. Given that the TOD clock can jump forward and backward
due to STP sync checks the order of debug events can get obfuscated.

Replace the absolute TOD time stamps with a delta to the IPL time
stamp. On a STP sync check the TOD clock correction is added to
the IPL time stamp as well to make the deltas unaffected by STP
sync check.

The readout of the debug feature entries will convert the deltas
back to absolute time stamps based on the Unix epoch.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/timex.h

@@ -178,14 +178,6 @@ int get_phys_clock(unsigned long long *clock);
 void init_cpu_timer(void);
 unsigned long long monotonic_clock(void);
 
-void tod_to_timeval(__u64 todval, struct timespec64 *xt);
-
-static inline
-void stck_to_timespec64(unsigned long long stck, struct timespec64 *ts)
-{
-	tod_to_timeval(stck - TOD_UNIX_EPOCH, ts);
-}
-
 extern u64 sched_clock_base_cc;
 
 /**

arch/s390/kernel/debug.c

@@ -866,7 +866,7 @@ static inline void
 debug_finish_entry(debug_info_t * id, debug_entry_t* active, int level,
 			int exception)
 {
-	active->id.stck = get_tod_clock_fast();
+	active->id.stck = get_tod_clock_fast() - sched_clock_base_cc;
 	active->id.fields.cpuid = smp_processor_id();
 	active->caller = __builtin_return_address(0);
 	active->id.fields.exception = exception;
@@ -1455,23 +1455,24 @@ int
 debug_dflt_header_fn(debug_info_t * id, struct debug_view *view,
 			 int area, debug_entry_t * entry, char *out_buf)
 {
-	struct timespec64 time_spec;
+	unsigned long sec, usec;
 	char *except_str;
 	unsigned long caller;
 	int rc = 0;
 	unsigned int level;
 
 	level = entry->id.fields.level;
-	stck_to_timespec64(entry->id.stck, &time_spec);
+	sec = (entry->id.stck >> 12) + (sched_clock_base_cc >> 12);
+	sec = sec - (TOD_UNIX_EPOCH >> 12);
+	usec = do_div(sec, USEC_PER_SEC);
 
 	if (entry->id.fields.exception)
 		except_str = "*";
 	else
 		except_str = "-";
 	caller = (unsigned long) entry->caller;
-	rc += sprintf(out_buf, "%02i %011lld:%06lu %1u %1s %02i %p  ",
-		      area, (long long)time_spec.tv_sec,
-		      time_spec.tv_nsec / 1000, level, except_str,
+	rc += sprintf(out_buf, "%02i %011ld:%06lu %1u %1s %02i %p  ",
+		      area, sec, usec, level, except_str,
 		      entry->id.fields.cpuid, (void *)caller);
 	return rc;
 }

arch/s390/kernel/time.c

@@ -110,7 +110,7 @@ unsigned long long monotonic_clock(void)
 }
 EXPORT_SYMBOL(monotonic_clock);
 
-void tod_to_timeval(__u64 todval, struct timespec64 *xt)
+static void tod_to_timeval(__u64 todval, struct timespec64 *xt)
 {
 	unsigned long long sec;
 
@@ -120,7 +120,6 @@ void tod_to_timeval(__u64 todval, struct timespec64 *xt)
 	todval -= (sec * 1000000) << 12;
 	xt->tv_nsec = ((todval * 1000) >> 12);
 }
-EXPORT_SYMBOL(tod_to_timeval);
 
 void clock_comparator_work(void)
 {