linux-kernel - Re: [PATCH v2 1/3] clocksource: davinci: only enable tim34 in periodic mode once it's initialized

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Date:   Fri, 10 Jan 2020 00:12:21 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Bartosz Golaszewski <brgl@...ev.pl>, Sekhar Nori <nsekhar@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        David Lechner <david@...hnology.com>,
        Kevin Hilman <khilman@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v2 1/3] clocksource: davinci: only enable tim34 in
 periodic mode once it's initialized

On 24/12/2019 11:03, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> 
> The DM365 platform has a strange quirk (only present when using ancient
> u-boot - mainline u-boot v2013.01 and later works fine) where if we
> enable the second half of the timer in periodic mode before we do its
> initialization - the time won't start flowing and we can't boot.
> 
> When using more recent u-boot, we can enable the timer, then reinitialize
> it and all works fine.
> 
> I've been unable to figure out why that is, but a workaround for this
> is straightforward - don't enable the tim34 timer in periodic mode until
> it's properly initialized.
> 
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
> ---
>  drivers/clocksource/timer-davinci.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/clocksource/timer-davinci.c b/drivers/clocksource/timer-davinci.c
> index 62745c962049..2801f21bb0e2 100644
> --- a/drivers/clocksource/timer-davinci.c
> +++ b/drivers/clocksource/timer-davinci.c
> @@ -62,6 +62,7 @@ static struct {
>  	struct clocksource dev;
>  	void __iomem *base;
>  	unsigned int tim_off;
> +	bool initialized;
>  } davinci_clocksource;
>  
>  static struct davinci_clockevent *
> @@ -94,8 +95,9 @@ static void davinci_tim12_shutdown(void __iomem *base)
>  	 * halves. In this case TIM34 runs in periodic mode and we must
>  	 * not modify it.
>  	 */
> -	tcr |= DAVINCI_TIMER_ENAMODE_PERIODIC <<
> -		DAVINCI_TIMER_ENAMODE_SHIFT_TIM34;
> +	if (likely(davinci_clocksource.initialized))
> +		tcr |= DAVINCI_TIMER_ENAMODE_PERIODIC <<
> +		       DAVINCI_TIMER_ENAMODE_SHIFT_TIM34;
>  
>  	writel_relaxed(tcr, base + DAVINCI_TIMER_REG_TCR);
>  }
> @@ -107,8 +109,9 @@ static void davinci_tim12_set_oneshot(void __iomem *base)
>  	tcr = DAVINCI_TIMER_ENAMODE_ONESHOT <<
>  		DAVINCI_TIMER_ENAMODE_SHIFT_TIM12;
>  	/* Same as above. */
> -	tcr |= DAVINCI_TIMER_ENAMODE_PERIODIC <<
> -		DAVINCI_TIMER_ENAMODE_SHIFT_TIM34;
> +	if (likely(davinci_clocksource.initialized))
> +		tcr |= DAVINCI_TIMER_ENAMODE_PERIODIC <<
> +		       DAVINCI_TIMER_ENAMODE_SHIFT_TIM34;
>  
>  	writel_relaxed(tcr, base + DAVINCI_TIMER_REG_TCR);
>  }
> @@ -206,6 +209,8 @@ static void davinci_clocksource_init_tim34(void __iomem *base)
>  	writel_relaxed(0x0, base + DAVINCI_TIMER_REG_TIM34);
>  	writel_relaxed(UINT_MAX, base + DAVINCI_TIMER_REG_PRD34);
>  	writel_relaxed(tcr, base + DAVINCI_TIMER_REG_TCR);
> +
> +	davinci_clocksource.initialized = true;
>  }

Why not move clockevents_config_and_register() after
davinci_clocksource_init_tim34() is called ?


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