linux-kernel - Re: [PATCH 1/3] clocksource: davinci: work around a clocksource problem on dm365 SoC

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Date:   Mon, 16 Dec 2019 11:58:31 -0600
From:   David Lechner <david@...hnology.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>, Sekhar Nori <nsekhar@...com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        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 1/3] clocksource: davinci: work around a clocksource
 problem on dm365 SoC

On 12/13/19 10:24 AM, 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 - just cache the enable bits for tim34.


I had a hard time groking this code. See suggested changes below for
something that would make the intention more clear (to me at least).


> 
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
> ---
>   drivers/clocksource/timer-davinci.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clocksource/timer-davinci.c b/drivers/clocksource/timer-davinci.c
> index 62745c962049..1c22443acaeb 100644
> --- a/drivers/clocksource/timer-davinci.c
> +++ b/drivers/clocksource/timer-davinci.c
> @@ -64,6 +64,8 @@ static struct {
>   	unsigned int tim_off;
>   } davinci_clocksource;
>   
> +static unsigned int davinci_clocksource_tim32_mode;

static unsigned bool davinci_clocksource_initialized;

> +
>   static struct davinci_clockevent *
>   to_davinci_clockevent(struct clock_event_device *clockevent)
>   {
> @@ -94,7 +96,7 @@ 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 <<
> +	tcr |= davinci_clocksource_tim32_mode <<
>   		DAVINCI_TIMER_ENAMODE_SHIFT_TIM34;

	if (davinci_clocksource_initialized)
		tcr |= DAVINCI_TIMER_ENAMODE_PERIODIC <<
			DAVINCI_TIMER_ENAMODE_SHIFT_TIM34;

>   
>   	writel_relaxed(tcr, base + DAVINCI_TIMER_REG_TCR);
> @@ -107,7 +109,7 @@ 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 <<
> +	tcr |= davinci_clocksource_tim32_mode <<
>   		DAVINCI_TIMER_ENAMODE_SHIFT_TIM34;

	if (davinci_clocksource_initialized)
		tcr |= DAVINCI_TIMER_ENAMODE_PERIODIC <<
			DAVINCI_TIMER_ENAMODE_SHIFT_TIM34;

>   
>   	writel_relaxed(tcr, base + DAVINCI_TIMER_REG_TCR);
> @@ -206,6 +208,8 @@ 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_tim32_mode = DAVINCI_TIMER_ENAMODE_PERIODIC;


	davinci_clocksource_initialized  = true;

>   }
>   
>   /*
>