diff options
| 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/include/asm/setup.h | |
| parent | 45be0a02f8110a13502fac6167a893c7c0eff432 (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>
Diffstat (limited to 'arch/s390/include/asm/setup.h')
| -rw-r--r-- | arch/s390/include/asm/setup.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/s390/include/asm/setup.h b/arch/s390/include/asm/setup.h index 49c425903894..61da4bd6edad 100644 --- a/arch/s390/include/asm/setup.h +++ b/arch/s390/include/asm/setup.h @@ -32,6 +32,7 @@ #define MACHINE_FLAG_TLB_GUEST _BITUL(14) #define MACHINE_FLAG_NX _BITUL(15) #define MACHINE_FLAG_GS _BITUL(16) +#define MACHINE_FLAG_SCC _BITUL(17) #define LPP_MAGIC _BITUL(31) #define LPP_PFAULT_PID_MASK _AC(0xffffffff, UL) @@ -72,6 +73,7 @@ extern void detect_memory_memblock(void); #define MACHINE_HAS_TLB_GUEST (S390_lowcore.machine_flags & MACHINE_FLAG_TLB_GUEST) #define MACHINE_HAS_NX (S390_lowcore.machine_flags & MACHINE_FLAG_NX) #define MACHINE_HAS_GS (S390_lowcore.machine_flags & MACHINE_FLAG_GS) +#define MACHINE_HAS_SCC (S390_lowcore.machine_flags & MACHINE_FLAG_SCC) /* * Console mode. Override with conmode= |