pps: add parallel port PPS signal generator

[pandora-kernel.git] / drivers / pps / generators / pps_gen_parport.c

diff --git a/drivers/pps/generators/pps_gen_parport.c b/drivers/pps/generators/pps_gen_parport.c
index a15fe25..5c32f8d 100644 (file)
--- a/drivers/pps/generators/pps_gen_parport.c
+++ b/drivers/pps/generators/pps_gen_parport.c
@@ -76,8 +76,15 @@ static enum hrtimer_restart hrtimer_event(struct hrtimer *timer)
        long lim, delta;
        unsigned long flags;
 
-       /* NB: approx time with blocked interrupts =
-          send_delay + 3 * SAFETY_INTERVAL */
+       /* We have to disable interrupts here. The idea is to prevent
+        * other interrupts on the same processor to introduce random
+        * lags while polling the clock. getnstimeofday() takes <1us on
+        * most machines while other interrupt handlers can take much
+        * more potentially.
+        *
+        * NB: approx time with blocked interrupts =
+        * send_delay + 3 * SAFETY_INTERVAL
+        */
        local_irq_save(flags);
 
        /* first of all we get the time stamp... */