linux-kernel - Re: [PATCH] clocksource/drivers/timer-mediatek: optimize systimer irq clear flow on Mediatek Socs

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Date:   Mon, 22 Mar 2021 11:10:50 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Fengquan Chen <Fengquan.Chen@...iatek.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Cc:     dehui.sun@...iatek.com
Subject: Re: [PATCH] clocksource/drivers/timer-mediatek: optimize systimer irq
 clear flow on Mediatek Socs

On 02/03/2021 08:28, Fengquan Chen wrote:
> 1)ensure systimer is enabled before clear and disable interrupt, which only
> for systimer in Mediatek Socs.
>
> 2)clear any pending timer-irq when shutdown to keep suspend flow clean,
> when use systimer as tick-broadcast timer
> 
> Change-Id: Ia3eda83324af2fdaf5cbb3569a9bf020a11f8009

Remove the above.

Add a Fixes tag.

> Signed-off-by: Fengquan Chen <fengquan.chen@...iatek.com>
> ---
>  drivers/clocksource/timer-mediatek.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/clocksource/timer-mediatek.c b/drivers/clocksource/timer-mediatek.c
> index 9318edc..9f1f095dc 100644
> --- a/drivers/clocksource/timer-mediatek.c
> +++ b/drivers/clocksource/timer-mediatek.c
> @@ -75,6 +75,7 @@
>  static void mtk_syst_ack_irq(struct timer_of *to)
>  {
>  	/* Clear and disable interrupt */
> +	writel(SYST_CON_EN, SYST_CON_REG(to));

	SYST_CON_EN is set below, why do you have to do it before?

Is that a hw bug ?

It is confusing what the description of the SYST_CON_EN says:

/*
 * SYST_CON_EN: Clock enable. Shall be set to
 *   - Start timer countdown.
 *   - Allow timeout ticks being updated.
 *   - Allow changing interrupt functions.

What means "interrupt functions" ?

Does writing writel(SYST_CON_EN, SYST_CON_REG(to)) before
SYST_CON_IRQ_CLR allows to clear the interrupt flag?

Can you explain how the timer works regarding this part?

It sounds to me a bit strange.

 *
 * SYST_CON_IRQ_EN: Set to allow interrupt.
 *
 * SYST_CON_IRQ_CLR: Set to clear interrupt.
 */


>  	writel(SYST_CON_IRQ_CLR | SYST_CON_EN, SYST_CON_REG(to));
>  }
>  
> @@ -111,6 +112,9 @@ static int mtk_syst_clkevt_next_event(unsigned long ticks,
>  
>  static int mtk_syst_clkevt_shutdown(struct clock_event_device *clkevt)
>  {
> +	/* Clear any irq */
> +	mtk_syst_ack_irq(to_timer_of(clkevt));
> +
>  	/* Disable timer */
>  	writel(0, SYST_CON_REG(to_timer_of(clkevt)));
>  
> 


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