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Commit 8adbf78e authored by Martin Schwidefsky's avatar Martin Schwidefsky
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s390,time: revert direct ktime path for s390 clockevent device 



Git commit 4f37a68c
"s390: Use direct ktime path for s390 clockevent device" makes use
of the CLOCK_EVT_FEAT_KTIME clockevent option to avoid the delta
calculation with ktime_get() in clockevents_program_event and the
get_tod_clock() in s390_next_event. This is based on the assumption
that the difference between the internal ktime and the hardware
clock is reflected in the wall_to_monotonic delta. But this is not
true, the ntp corrections are applied via changes to the tk->mult
multiplier and this is not reflected in wall_to_monotonic.

In theory this could be solved by using the raw monotonic clock
but it is simpler to switch back to the standard clock delta
calculation.

Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 79c74ecb

arch/s390/kernel/time.c

+4 −15
Original line number Diff line number Diff line
@@ -108,20 +108,10 @@ static void fixup_clock_comparator(unsigned long long delta) 
	set_clock_comparator(S390_lowcore.clock_comparator);

}



static int s390_next_ktime(ktime_t expires,

static int s390_next_event(unsigned long delta,

			   struct clock_event_device *evt)

{

	struct timespec ts;

	u64 nsecs;



	ts.tv_sec = ts.tv_nsec = 0;

	monotonic_to_bootbased(&ts);

	nsecs = ktime_to_ns(ktime_add(timespec_to_ktime(ts), expires));

	do_div(nsecs, 125);

	S390_lowcore.clock_comparator = sched_clock_base_cc + (nsecs << 9);

	/* Program the maximum value if we have an overflow (== year 2042) */

	if (unlikely(S390_lowcore.clock_comparator < sched_clock_base_cc))

		S390_lowcore.clock_comparator = -1ULL;

	S390_lowcore.clock_comparator = get_tod_clock() + delta;

	set_clock_comparator(S390_lowcore.clock_comparator);

	return 0;

}
@@ -146,15 +136,14 @@ void init_cpu_timer(void) 
	cpu = smp_processor_id();

	cd = &per_cpu(comparators, cpu);

	cd->name		= "comparator";

	cd->features		= CLOCK_EVT_FEAT_ONESHOT |

				  CLOCK_EVT_FEAT_KTIME;

	cd->features		= CLOCK_EVT_FEAT_ONESHOT;

	cd->mult		= 16777;

	cd->shift		= 12;

	cd->min_delta_ns	= 1;

	cd->max_delta_ns	= LONG_MAX;

	cd->rating		= 400;

	cd->cpumask		= cpumask_of(cpu);

	cd->set_next_ktime	= s390_next_ktime;

	cd->set_next_event	= s390_next_event;

	cd->set_mode		= s390_set_mode;



	clockevents_register_device(cd);