s390/time: add support for the TOD clock epoch extension

The TOD epoch extension adds 8 epoch bits to the TOD clock to provide
a continuous clock after 2042/09/17. The store-clock-extended (STCKE)
instruction will store the epoch index in the first byte of the
16 bytes stored by the instruction. The read_boot_clock64 and the
read_presistent_clock64 functions need to take the additional bits
into account to give the correct result after 2042/09/17.

The clock-comparator register will stay 64 bit wide. The comparison
of the clock-comparator with the TOD clock is limited to bytes
1 to 8 of the extended TOD format. To deal with the overflow problem
due to an epoch change the clock-comparator sign control in CR0 can
be used to switch the comparison of the 64-bit TOD clock with the
clock-comparator to a signed comparison.

The decision between the signed vs. unsigned clock-comparator
comparisons is done at boot time. Only if the TOD clock is in the
second half of a 142 year epoch the signed comparison is used.
This solves the epoch overflow issue as long as the machine is
booted at least once in an epoch.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/arch/s390/kernel/debug.c b/arch/s390/kernel/debug.c
index 86b3e74f569e..1d9e83c401fc 100644
--- a/arch/s390/kernel/debug.c
+++ b/arch/s390/kernel/debug.c
@@ -866,7 +866,8 @@ 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() - sched_clock_base_cc;
+	active->id.stck = get_tod_clock_fast() -
+		*(unsigned long long *) &tod_clock_base[1];
 	active->id.fields.cpuid = smp_processor_id();
 	active->caller = __builtin_return_address(0);
 	active->id.fields.exception = exception;
@@ -1455,15 +1456,15 @@ int
 debug_dflt_header_fn(debug_info_t * id, struct debug_view *view,
 			 int area, debug_entry_t * entry, char *out_buf)
 {
-	unsigned long sec, usec;
+	unsigned long base, sec, usec;
 	char *except_str;
 	unsigned long caller;
 	int rc = 0;
 	unsigned int level;
 
 	level = entry->id.fields.level;
-	sec = (entry->id.stck >> 12) + (sched_clock_base_cc >> 12);
-	sec = sec - (TOD_UNIX_EPOCH >> 12);
+	base = (*(unsigned long *) &tod_clock_base[0]) >> 4;
+	sec = (entry->id.stck >> 12) + base - (TOD_UNIX_EPOCH >> 12);
 	usec = do_div(sec, USEC_PER_SEC);
 
 	if (entry->id.fields.exception)