clocksource: samsung_pwm_timer: Work around rounding errors in clockevents core

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 <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Olof Johansson <olof@lixom.net>

diff --git a/drivers/clocksource/samsung_pwm_timer.c b/drivers/clocksource/samsung_pwm_timer.c
index 92b2f130ae9bb399dc1c6fa63d655f405df9b253..0234c8d2c8f26ccefc187be2385f103e8197f48c 100644 (file)
--- 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);