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>

1 files changed, 34 insertions, 4 deletions

diff --git a/arch/s390/include/asm/timex.h b/arch/s390/include/asm/timex.h
index 118535123f34..0ea03c11458d 100644
--- a/arch/s390/include/asm/timex.h
+++ b/arch/s390/include/asm/timex.h
@@ -15,6 +15,8 @@
 /* The value of the TOD clock for 1.1.1970. */
 #define TOD_UNIX_EPOCH 0x7d91048bca000000ULL
 
+extern u64 clock_comparator_max;
+
 /* Inline functions for clock register access. */
 static inline int set_tod_clock(__u64 time)
 {
@@ -126,7 +128,7 @@ static inline unsigned long long local_tick_disable(void)
 	unsigned long long old;
 
 	old = S390_lowcore.clock_comparator;
-	S390_lowcore.clock_comparator = -1ULL;
+	S390_lowcore.clock_comparator = clock_comparator_max;
 	set_clock_comparator(S390_lowcore.clock_comparator);
 	return old;
 }
@@ -178,20 +180,20 @@ int get_phys_clock(unsigned long long *clock);
 void init_cpu_timer(void);
 unsigned long long monotonic_clock(void);
 
-extern u64 sched_clock_base_cc;
+extern unsigned char tod_clock_base[16] __aligned(8);
 
 /**
  * get_clock_monotonic - returns current time in clock rate units
  *
  * The caller must ensure that preemption is disabled.
- * The clock and sched_clock_base get changed via stop_machine.
+ * The clock and tod_clock_base get changed via stop_machine.
  * Therefore preemption must be disabled when calling this
  * function, otherwise the returned value is not guaranteed to
  * be monotonic.
  */
 static inline unsigned long long get_tod_clock_monotonic(void)
 {
-	return get_tod_clock() - sched_clock_base_cc;
+	return get_tod_clock() - *(unsigned long long *) &tod_clock_base[1];
 }
 
 /**
@@ -218,4 +220,32 @@ static inline unsigned long long tod_to_ns(unsigned long long todval)
 	return ((todval >> 9) * 125) + (((todval & 0x1ff) * 125) >> 9);
 }
 
+/**
+ * tod_after - compare two 64 bit TOD values
+ * @a: first 64 bit TOD timestamp
+ * @b: second 64 bit TOD timestamp
+ *
+ * Returns: true if a is later than b
+ */
+static inline int tod_after(unsigned long long a, unsigned long long b)
+{
+	if (MACHINE_HAS_SCC)
+		return (long long) a > (long long) b;
+	return a > b;
+}
+
+/**
+ * tod_after_eq - compare two 64 bit TOD values
+ * @a: first 64 bit TOD timestamp
+ * @b: second 64 bit TOD timestamp
+ *
+ * Returns: true if a is later than b
+ */
+static inline int tod_after_eq(unsigned long long a, unsigned long long b)
+{
+	if (MACHINE_HAS_SCC)
+		return (long long) a >= (long long) b;
+	return a >= b;
+}
+
 #endif