[PATCH 22/25] clocksource/drivers/tegra: Cycles can't be 0

From: Daniel Lezcano
Date: Wed Jun 26 2019 - 10:48:19 EST


From: Dmitry Osipenko <digetx@xxxxxxxxx>

Tegra's timer uses n+1 scheme for the counter, i.e. timer will fire after
one tick if 0 is loaded. The minimum and maximum numbers of oneshot ticks
are defined by clockevents_config_and_register(min, max) invocation and
the min value is set to 1 tick. Hence "cycles" value can't ever be 0,
unless it's a bug in clocksource core.

Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
Acked-by: Jon Hunter <jonathanh@xxxxxxxxxx>
Acked-by: Thierry Reding <treding@xxxxxxxxxx>
Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
---
drivers/clocksource/timer-tegra.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/clocksource/timer-tegra.c b/drivers/clocksource/timer-tegra.c
index 8e70f38f1898..a907e71065bd 100644
--- a/drivers/clocksource/timer-tegra.c
+++ b/drivers/clocksource/timer-tegra.c
@@ -56,9 +56,16 @@ static int tegra_timer_set_next_event(unsigned long cycles,
{
void __iomem *reg_base = timer_of_base(to_timer_of(evt));

- writel_relaxed(TIMER_PTV_EN |
- ((cycles > 1) ? (cycles - 1) : 0), /* n+1 scheme */
- reg_base + TIMER_PTV);
+ /*
+ * Tegra's timer uses n+1 scheme for the counter, i.e. timer will
+ * fire after one tick if 0 is loaded.
+ *
+ * The minimum and maximum numbers of oneshot ticks are defined
+ * by clockevents_config_and_register(1, 0x1fffffff + 1) invocation
+ * below in the code. Hence the cycles (ticks) can't be outside of
+ * a range supportable by hardware.
+ */
+ writel_relaxed(TIMER_PTV_EN | (cycles - 1), reg_base + TIMER_PTV);

return 0;
}
--
2.17.1