linux-kernel - Re: [PATCH v8 4/6] clocksource: stm32: only use 32 bits timers

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Message-ID: <f22fd299-a742-1144-75d0-256a538af619@linaro.org>
Date:   Fri, 8 Dec 2017 09:34:44 +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 4/6] clocksource: stm32: only use 32 bits timers

On 14/11/2017 09:52, Benjamin Gaignard wrote:
> The clock driving counters is at 90MHz so the maximum period
> for 16 bis counters is around 750 ms

728 us

> which is a short period for a clocksource.

Which clocksource are you talking about ?

> For 32 bits counters this period is close
> 47 secondes which is more acceptable.
> 
> This patch remove 16 bits counters support and makes sure that
> they won't be probed anymore.

Are we talking about clockevent or clocksource?

Is this issue present today ? Or is it if we add the clocksource support
? We are talking about clocksource but we change the clockevent code.

All this is very confusing.

I have a rough idea of what is happening, but it is not up to me to
decode and infer from the changes, you need to describe *clearly* the
situation.

 - What happens if we use a 16bits timer as a clockevent ?
 - What happens if we use a 16bits timer as a clocksource ?
 - Why is it preferable to remove the support of the 16bits timers
instead of downgrading them with the rating ?

> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...aro.org>

> ---
>  drivers/clocksource/timer-stm32.c | 26 ++++++++++++--------------
>  1 file changed, 12 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/clocksource/timer-stm32.c b/drivers/clocksource/timer-stm32.c
> index ae41a19..8173bcf 100644
> --- a/drivers/clocksource/timer-stm32.c
> +++ b/drivers/clocksource/timer-stm32.c
> @@ -83,9 +83,9 @@ static irqreturn_t stm32_clock_event_handler(int irq, void *dev_id)
>  static int __init stm32_clockevent_init(struct device_node *node)
>  {
>  	struct reset_control *rstc;
> -	unsigned long max_delta;
> -	int ret, bits, prescaler = 1;
> +	unsigned long max_arr;
>  	struct timer_of *to;
> +	int ret;
>  
>  	to = kzalloc(sizeof(*to), GFP_KERNEL);
>  	if (!to)
> @@ -115,29 +115,27 @@ static int __init stm32_clockevent_init(struct device_node *node)
>  
>  	/* 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;
> -		bits = 32;
> -	} else {
> -		prescaler = 1024;
> -		bits = 16;
> +	max_arr = readl_relaxed(timer_of_base(to) + TIM_ARR);
> +	if (max_arr != ~0U) {
> +		pr_err("32 bits timer is needed\n");
> +		ret = -EINVAL;
> +		goto deinit;
>  	}

Wrap this in a function:

static bool stm32_timer_is_32bits(struct timer_of *to)
{
	return readl_relaxed(timer_of_base(to) + TIM_ARR) == ~0UL;
}

Then clearly inform the user.

if (!stm32_timer_is_32bits(to)) {
	pr_warn("Timer %pOF is a 16 bits timer\n", node);
	/* abort the registration or downgrade the timer's rating */
}

> +
>  	writel_relaxed(0, timer_of_base(to) + TIM_ARR);
>  
> -	writel_relaxed(prescaler - 1, timer_of_base(to) + TIM_PSC);
> +	writel_relaxed(0, timer_of_base(to) + TIM_PSC);
>  	writel_relaxed(TIM_EGR_UG, timer_of_base(to) + TIM_EGR);
>  	writel_relaxed(TIM_DIER_UIE, timer_of_base(to) + TIM_DIER);
>  	writel_relaxed(0, timer_of_base(to) + TIM_SR);
>  
>  	clockevents_config_and_register(&to->clkevt,
> -					timer_of_period(to), MIN_DELTA, max_delta);
> -
> -	pr_info("%pOF: STM32 clockevent driver initialized (%d bits)\n",
> -			node, bits);
> +					timer_of_period(to), MIN_DELTA, ~0U);
>  
>  	return 0;
>  
> +deinit:
> +	timer_of_exit(to);

Fix this please (timer_of_cleanup).

In the future, make sure the patches are git-bisect safe.



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