pps: add parallel port PPS signal generator

Add PPS signal generator which utilizes STROBE pin of a parallel port to
send PPS signals.  It uses parport abstraction layer and hrtimers to
precisely control the signal.

Signed-off-by: Alexander Gordeev <lasaine@lvk.cs.msu.su>
Cc: Rodolfo Giometti <giometti@linux.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 10 insertions, 7 deletions

diff --git a/drivers/pps/generators/Kconfig b/drivers/pps/generators/Kconfig
index 5fbd6148c804..f3a73dd77660 100644
--- a/drivers/pps/generators/Kconfig
+++ b/drivers/pps/generators/Kconfig
@@ -2,16 +2,12 @@
 # PPS generators configuration
 #
 
-if PPS
-
 comment "PPS generators support"
 
 config PPS_GENERATOR_PARPORT
         tristate "Parallel port PPS signal generator"
-        depends on PARPORT != n && GENERIC_TIME
+        depends on PARPORT
         help
           If you say yes here you get support for a PPS signal generator which
           utilizes STROBE pin of a parallel port to send PPS signals. It uses
           parport abstraction layer and hrtimers to precisely control the signal.
-
-endif
diff --git a/drivers/pps/generators/pps_gen_parport.c b/drivers/pps/generators/pps_gen_parport.c
index a15fe25efd55..5c32f8dacf56 100644
--- 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... */