diff options
author | Benjamin Gaignard <benjamin.gaignard@st.com> | 2018-01-04 13:03:00 +0100 |
---|---|---|
committer | Daniel Lezcano <daniel.lezcano@linaro.org> | 2018-01-08 12:10:02 +0100 |
commit | b9712bd04a18afd5aadbd1259f70833b772c874d (patch) | |
tree | 6bc279ae5f1e5a4e0e3931cf1aed76acb43a1439 | |
parent | 776a8af9f130de0fe6324e967b13306c260335a4 (diff) |
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 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.
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Tested-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Acked-by: Benjamin Gaignard <benjamin.gaignard@st.com>
-rw-r--r-- | drivers/clocksource/timer-stm32.c | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/drivers/clocksource/timer-stm32.c b/drivers/clocksource/timer-stm32.c index 862134e0b1be..ac558960ae4e 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); |