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/head64.S | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch/s390/kernel/head64.S') diff --git a/arch/s390/kernel/head64.S b/arch/s390/kernel/head64.S index 31c91f24e562..0d8f2a858ced 100644 --- a/arch/s390/kernel/head64.S +++ b/arch/s390/kernel/head64.S @@ -21,8 +21,8 @@ ENTRY(startup_continue) xc __LC_LPP+1(7,0),__LC_LPP+1 # clear lpp and current_pid mvi __LC_LPP,0x80 # and set LPP_MAGIC .insn s,0xb2800000,__LC_LPP # load program parameter -0: larl %r1,sched_clock_base_cc - mvc 0(8,%r1),__LC_LAST_UPDATE_CLOCK +0: larl %r1,tod_clock_base + mvc 0(16,%r1),__LC_BOOT_CLOCK larl %r13,.LPG1 # get base lctlg %c0,%c15,.Lctl-.LPG1(%r13) # load control registers lg %r12,.Lparmaddr-.LPG1(%r13) # pointer to parameter area -- cgit