[v3,09/13] clocksource: samsung_pwm_timer: Work around rounding errors in clockevents core

Commit Message

Tomasz Figa April 23, 2013, 3:46 p.m. UTC

Due to rounding errors in clockevents core (in conversions between ticks
and nsecs), it might happen that the set_next_event callback gets called
with cycles = 0, causing the code to incorrectly program the PWM timer.

This patch modifies the callback to program the timer for 1 tick, if
received tick count value is 0.

Signed-off-by: Tomasz Figa <[e-mail]>
Signed-off-by: Kyungmin Park <[e-mail]>
---
 drivers/clocksource/samsung_pwm_timer.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

Patch

diff --git a/drivers/clocksource/samsung_pwm_timer.c b/drivers/clocksource/samsung_pwm_timer.c
index 92b2f13..0234c8d 100644
--- a/drivers/clocksource/samsung_pwm_timer.c
+++ b/drivers/clocksource/samsung_pwm_timer.c
@@ -176,6 +176,19 @@  static void samsung_time_start(unsigned int channel, bool periodic)
 static int samsung_set_next_event(unsigned long cycles,
 				struct clock_event_device *evt)
 {
+	/*
+	 * This check is needed to account for internal rounding
+	 * errors inside clockevents core, which might result in
+	 * passing cycles = 0, which in turn would not generate any
+	 * timer interrupt and hang the system.
+	 *
+	 * Another solution would be to set up the clockevent device
+	 * with min_delta = 2, but this would unnecessarily increase
+	 * the minimum sleep period.
+	 */
+	if (!cycles)
+		cycles = 1;
+
 	samsung_time_setup(pwm.event_id, cycles);
 	samsung_time_start(pwm.event_id, false);