Messages in this thread Patch in this message | | | From | Benjamin Gaignard <> | Subject | [PATCH 2/4] clocksource: stm32: use prescaler to adjust the resolution | Date | Fri, 15 Dec 2017 09:52:45 +0100 |
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Rather than use fixed prescaler values compute it to get a clock as close as possible of 10KHz and a resolution of 0.1ms.
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com> --- drivers/clocksource/timer-stm32.c | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-)
diff --git a/drivers/clocksource/timer-stm32.c b/drivers/clocksource/timer-stm32.c index 23a321cca45b..de721d318065 100644 --- a/drivers/clocksource/timer-stm32.c +++ b/drivers/clocksource/timer-stm32.c @@ -37,6 +37,11 @@ #define TIM_EGR_UG BIT(0) +#define MAX_TIM_PSC 0xFFFF + +/* Target a 10KHz clock to get a resolution of 0.1 ms */ +#define TARGETED_CLK_RATE 10000 + static int stm32_clock_event_shutdown(struct clock_event_device *evt) { struct timer_of *to = to_timer_of(evt); @@ -83,7 +88,7 @@ static irqreturn_t stm32_clock_event_handler(int irq, void *dev_id) static void __init stm32_clockevent_init(struct timer_of *to) { unsigned long max_delta; - int prescaler; + unsigned long prescaler; to->clkevt.name = "stm32_clockevent"; to->clkevt.features = CLOCK_EVT_FEAT_PERIODIC; @@ -96,13 +101,17 @@ static void __init stm32_clockevent_init(struct timer_of *to) /* Detect whether the timer is 16 or 32 bits */ writel_relaxed(~0U, timer_of_base(to) + TIM_ARR); max_delta = readl_relaxed(timer_of_base(to) + TIM_ARR); - if (max_delta == ~0U) { - prescaler = 1; + to->clkevt.rating = 50; + if (max_delta == ~0U) to->clkevt.rating = 250; - } else { - prescaler = 1024; - to->clkevt.rating = 50; - } + + /* + * Get the highest possible prescaler value to be as close + * as possible of TARGETED_CLK_RATE + */ + prescaler = DIV_ROUND_CLOSEST(timer_of_rate(to), TARGETED_CLK_RATE); + if (prescaler > MAX_TIM_PSC) + prescaler = MAX_TIM_PSC; writel_relaxed(0, timer_of_base(to) + TIM_ARR); writel_relaxed(prescaler - 1, timer_of_base(to) + TIM_PSC); -- 2.15.0
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