Commit-ID: 4744daa10dcd3a1470fbeba4945fbf44dcb1b0d1
Gitweb: https://git.kernel.org/tip/4744daa10dcd3a1470fbeba4945fbf44dcb1b0d1
Author: Benjamin Gaignard <benjamin.gaignard@xxxxxx>
AuthorDate: Mon, 8 Jan 2018 14:28:54 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 8 Jan 2018 17:57:25 +0100
clocksource/drivers/stm32: Compute a prescaler value with a targeted rate
The prescaler value is arbitrarily set to 1024 without any regard to the
timer frequency. For 32-bit timers, there is no need to set a prescaler
value as they wrap in an acceptable interval and give the opportunity to
have precise timers on this platform. However, for 16-bit timers a prescaler
value is needed if we don't want to wrap too often per second which is
inefficient and adds more and more error margin. With a targeted clock
of 10MHz, the 16 bits are precise enough whatever the timer frequency is
as we will compute the prescaler.
Tested-by: Benjamin Gaignard <benjamin.gaignard@xxxxxx>
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@xxxxxx>
Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
Acked-by: Benjamin Gaignard <benjamin.gaignard@xxxxxx>
Cc: Alexandre Torgue <alexandre.torgue@xxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1515418139-23276-15-git-send-email-daniel.lezcano@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
drivers/clocksource/timer-stm32.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/drivers/clocksource/timer-stm32.c b/drivers/clocksource/timer-stm32.c
index 33c7c90..928ac28 100644
--- a/drivers/clocksource/timer-stm32.c
+++ b/drivers/clocksource/timer-stm32.c
@@ -37,6 +37,9 @@
#define TIM_EGR_UG BIT(0)
+#define TIM_PSC_MAX USHRT_MAX
+#define TIM_PSC_CLKRATE 10000
+
static int stm32_clock_event_shutdown(struct clock_event_device *clkevt)
{
struct timer_of *to = to_timer_of(clkevt);
@@ -116,7 +119,14 @@ static void __init stm32_clockevent_init(struct timer_of *to)
prescaler = 1;
to->clkevt.rating = 250;
} else {
- prescaler = 1024;
+ prescaler = DIV_ROUND_CLOSEST(timer_of_rate(to),
+ TIM_PSC_CLKRATE);
+ /*
+ * The prescaler register is an u16, the variable
+ * can't be greater than TIM_PSC_MAX, let's cap it in
+ * this case.
+ */
+ prescaler = prescaler < TIM_PSC_MAX ? prescaler : TIM_PSC_MAX;
to->clkevt.rating = 100;
}
writel_relaxed(0, timer_of_base(to) + TIM_ARR);
--
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