path: root/arch/s390/Makefile
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authorMartin Schwidefsky <schwidefsky@de.ibm.com>2016-10-27 12:41:39 +0200
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2017-07-26 08:25:14 +0200
commit6e2ef5e4f6cc57344762932d70d38ba4ec65fa8b (patch)
tree51e148a3b1e6991260af2ac51e6b1a6d5eb0f83a /arch/s390/Makefile
parents390/sclp: single increment assignment control (diff)
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>
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