Commit-ID: 4744daa10dcd3a1470fbeba4945fbf44dcb1b0d1 Gitweb: https://git.kernel.org/tip/4744daa10dcd3a1470fbeba4945fbf44dcb1b0d1 Author: Benjamin Gaignard <[email protected]> AuthorDate: Mon, 8 Jan 2018 14:28:54 +0100 Committer: Ingo Molnar <[email protected]> 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 <[email protected]> Signed-off-by: Benjamin Gaignard <[email protected]> Signed-off-by: Daniel Lezcano <[email protected]> Acked-by: Benjamin Gaignard <[email protected]> Cc: Alexandre Torgue <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Maxime Coquelin <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[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 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);
