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author | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2016-10-27 13:41:39 +0300 |
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committer | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2017-07-26 09:25:14 +0300 |
commit | 6e2ef5e4f6cc57344762932d70d38ba4ec65fa8b (patch) | |
tree | 51e148a3b1e6991260af2ac51e6b1a6d5eb0f83a /arch/c6x/include | |
parent | 45be0a02f8110a13502fac6167a893c7c0eff432 (diff) | |
download | linux-6e2ef5e4f6cc57344762932d70d38ba4ec65fa8b.tar.xz |
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/c6x/include')
0 files changed, 0 insertions, 0 deletions