linux-kernel - Re: [PATCH v1] arm: clocksource: Check if timer is enabled for timer irq

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Date:   Thu, 11 Aug 2022 10:49:35 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Ayan Kumar Halder <ayankuma@....com>
Cc:     <stefano.stabellini@...inx.com>, <sstabellini@...nel.org>,
        <julien@....org>, <bertrand.marquis@....com>,
        <mark.rutland@....com>, <daniel.lezcano@...aro.org>,
        <tglx@...utronix.de>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] arm: clocksource: Check if timer is enabled for timer irq

On Thu, 11 Aug 2022 10:36:20 +0100,
Ayan Kumar Halder <ayankuma@....com> wrote:
> 
> Refer ARM DDI 0487G.b, CNTP_CTL_EL0,
> ISTATUS, bit [2] - When the value of the ENABLE bit is 1, ISTATUS
> indicates whether the timer condition is met.
> 
> Thus, one need to check ENABLE bit along with ISTATUS, to confirm
> whether the timer condition is met. Further as the doc says,
> "When the value of the ENABLE bit is 0, the ISTATUS field is UNKNOWN."
> 
> Signed-off-by: Ayan Kumar Halder <ayankuma@....com>
> ---
> 
> Please refer to https://lore.kernel.org/all/6cfcd4fa-3afd-1c70-6a70-9df557ee1811@xen.org/T/
> for the previous discussion on this issue on xen-devel mailing list.
> 
>  drivers/clocksource/arm_arch_timer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 9ab8221ee3c6..96921772814c 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -647,7 +647,7 @@ static __always_inline irqreturn_t timer_handler(const int access,
>  	unsigned long ctrl;
>  
>  	ctrl = arch_timer_reg_read(access, ARCH_TIMER_REG_CTRL, evt);
> -	if (ctrl & ARCH_TIMER_CTRL_IT_STAT) {
> +	if ((ctrl & ARCH_TIMER_CTRL_IT_STAT) && (ctrl & ARCH_TIMER_CTRL_ENABLE)) {
>  		ctrl |= ARCH_TIMER_CTRL_IT_MASK;
>  		arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, evt);
>  		evt->event_handler(evt);

And how can the timer be disabled if we're in the interrupt handler?

	M.

-- 
Without deviation from the norm, progress is not possible.