linux-kernel - Re: [PATCH v3 8/8] clocksource/drivers/tegra: Set up maximum-ticks limit properly

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Date:   Tue, 18 Jun 2019 18:52:33 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        "Peter De Schrijver" <pdeschrijver@...dia.com>
CC:     <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 8/8] clocksource/drivers/tegra: Set up maximum-ticks
 limit properly


On 18/06/2019 15:03, Dmitry Osipenko wrote:
> Tegra's timer has 29 bits for the counter and for the "load" register
> which sets counter to a load-value. The counter's value is lower than
> the actual value by 1 because it starts to decrement after one tick,
> hence the maximum number of ticks that hardware can handle equals to
> 29 bits + 1.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/clocksource/timer-tegra.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clocksource/timer-tegra.c b/drivers/clocksource/timer-tegra.c
> index b84324288749..355b29ff6362 100644
> --- a/drivers/clocksource/timer-tegra.c
> +++ b/drivers/clocksource/timer-tegra.c
> @@ -137,9 +137,17 @@ static int tegra_timer_setup(unsigned int cpu)
>  	irq_force_affinity(to->clkevt.irq, cpumask_of(cpu));
>  	enable_irq(to->clkevt.irq);
>  
> +	/*
> +	 * Tegra's timer uses n+1 scheme for the counter, i.e. timer will
> +	 * fire after one tick if 0 is loaded and thus minimum number of
> +	 * ticks is 1. In result both of the clocksource's tick limits are
> +	 * higher than a minimum and maximum that hardware register can
> +	 * take by 1, this is then taken into account by set_next_event
> +	 * callback.
> +	 */
>  	clockevents_config_and_register(&to->clkevt, timer_of_rate(to),
>  					1, /* min */
> -					0x1fffffff); /* 29 bits */
> +					0x1fffffff + 1); /* max 29 bits + 1 */
>  
>  	return 0;
>  }
> 


Acked-by: Jon Hunter <jonathanh@...dia.com>

Cheers
Jon

-- 
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