linux-kernel - Re: [PATCH v8 3/6] clocksource: stm32: increase min delta value

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Message-ID: <4a9d9f25-ffcd-714c-c70f-ef1e9dbc8747@linaro.org>
Date:   Fri, 8 Dec 2017 10:28:15 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        robh+dt@...nel.org, mark.rutland@....com, linux@...linux.org.uk,
        mcoquelin.stm32@...il.com, alexandre.torgue@...com,
        tglx@...utronix.de, ludovic.barre@...com, julien.thierry@....com,
        sudeep.holla@....com, arnd@...db.de
Cc:     devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 3/6] clocksource: stm32: increase min delta value

On 14/11/2017 09:52, Benjamin Gaignard wrote:
> The CPU is a CortexM4 @ 200MHZ and the clocks driving
> the timers are at 90MHZ with a min delta at 1 you could
> have an interrupt each 0.01 ms which is really to much.
> By increase it to 0x60 it give more time (around 1 ms)
> to CPU to handle the interrupt.
> 
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...aro.org>
> ---
>  drivers/clocksource/timer-stm32.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clocksource/timer-stm32.c b/drivers/clocksource/timer-stm32.c
> index fc61fd1..ae41a19 100644
> --- a/drivers/clocksource/timer-stm32.c
> +++ b/drivers/clocksource/timer-stm32.c
> @@ -36,6 +36,8 @@
>  
>  #define TIM_EGR_UG	BIT(0)
>  
> +#define MIN_DELTA	0x60

Explain why 0x60 is a good value.

>  static int stm32_clock_event_shutdown(struct clock_event_device *evt)
>  {
>  	struct timer_of *to = to_timer_of(evt);
> @@ -129,7 +131,7 @@ static int __init stm32_clockevent_init(struct device_node *node)
>  	writel_relaxed(0, timer_of_base(to) + TIM_SR);
>  
>  	clockevents_config_and_register(&to->clkevt,
> -					timer_of_period(to), 0x1, max_delta);
> +					timer_of_period(to), MIN_DELTA, max_delta);
>  
>  	pr_info("%pOF: STM32 clockevent driver initialized (%d bits)\n",
>  			node, bits);
> 


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