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| author | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2016-10-27 12:41:39 +0200 |
|---|---|---|
| committer | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2017-07-26 08:25:14 +0200 |
| commit | 6e2ef5e4f6cc57344762932d70d38ba4ec65fa8b (patch) | |
| tree | 51e148a3b1e6991260af2ac51e6b1a6d5eb0f83a /arch/s390/kernel/head.S | |
| parent | 45be0a02f8110a13502fac6167a893c7c0eff432 (diff) | |
| download | linux-next-6e2ef5e4f6cc57344762932d70d38ba4ec65fa8b.tar.gz | |
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>
Diffstat (limited to 'arch/s390/kernel/head.S')
| -rw-r--r-- | arch/s390/kernel/head.S | 3 |
1 files changed, 2 insertions, 1 deletions
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) |