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/kernel/head.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'arch/s390/kernel/head.S') diff --git a/arch/s390/kernel/head.S b/arch/s390/kernel/head.S index eff5b31671d4..8ed753c72d9b 100644 --- a/arch/s390/kernel/head.S +++ b/arch/s390/kernel/head.S @@ -302,7 +302,8 @@ ENTRY(startup_kdump) xc 0xe00(256),0xe00 xc 0xf00(256),0xf00 lctlg %c0,%c15,0x200(%r0) # initialize control registers - stck __LC_LAST_UPDATE_CLOCK + stcke __LC_BOOT_CLOCK + mvc __LC_LAST_UPDATE_CLOCK(8),__LC_BOOT_CLOCK+1 spt 6f-.LPG0(%r13) mvc __LC_LAST_UPDATE_TIMER(8),6f-.LPG0(%r13) l %r15,.Lstack-.LPG0(%r13) -- cgit v1.2.1