clockevents: Add direct ktime programming function

There is at least one architecture (s390) with a sane clockevent device
that can be programmed with the equivalent of a ktime. No need to create
a delta against the current time, the ktime can be used directly.

A new clock device function 'set_next_ktime' is introduced that is called
with the unmodified ktime for the timer if the clock event device has the 
CLOCK_EVT_FEAT_KTIME bit set.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: john stultz <johnstul@us.ibm.com>
Link: http://lkml.kernel.org/r/20110823133142.815350967@de.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 4 insertions, 0 deletions

diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 713ef94eceef..1ecd6ba36d6c 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -216,6 +216,10 @@ int clockevents_program_event(struct clock_event_device *dev, ktime_t expires,
         if (dev->mode == CLOCK_EVT_MODE_SHUTDOWN)
                 return 0;
 
+        /* Shortcut for clockevent devices that can deal with ktime. */
+        if (dev->features & CLOCK_EVT_FEAT_KTIME)
+                return dev->set_next_ktime(expires, dev);
+
         delta = ktime_to_ns(ktime_sub(expires, ktime_get()));
         if (delta <= 0)
                 return force ? clockevents_program_min_delta(dev) : -ETIME;