From: Benjamin Gaignard <[email protected]> The prescaler value is arbitrarily set to 1024 without any regard to the timer frequency. For 32bits 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 16bits timers a prescaler value is needed if we don't want to wrap too often per second which is unefficient and adds more and more error margin. With a targeted clock of 10MHz, the 16bits are precise enough whatever the timer frequency is as we will compute the prescaler.
[Daniel Lezcano]: Massaged the changelog and added comment. Signed-off-by: Benjamin Gaignard <[email protected]> Signed-off-by: Daniel Lezcano <[email protected]> --- 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 862134e..ac55896 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); -- 2.7.4
