From 6e2ef5e4f6cc57344762932d70d38ba4ec65fa8b Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Thu, 27 Oct 2016 12:41:39 +0200 Subject: 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 --- arch/s390/lib/delay.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/s390/lib/delay.c') diff --git a/arch/s390/lib/delay.c b/arch/s390/lib/delay.c index 92e90e40b6fb..7f17555ad4d5 100644 --- a/arch/s390/lib/delay.c +++ b/arch/s390/lib/delay.c @@ -57,7 +57,7 @@ static void __udelay_enabled(unsigned long long usecs) end = get_tod_clock_fast() + (usecs << 12); do { clock_saved = 0; - if (end < S390_lowcore.clock_comparator) { + if (tod_after(S390_lowcore.clock_comparator, end)) { clock_saved = local_tick_disable(); set_clock_comparator(end); } -- cgit v1.2.3-59-g8ed1b