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

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Date:   Thu, 25 May 2023 17:03:11 +0100
From:   Ayan Kumar Halder <ayankuma@....com>
To:     Marc Zyngier <maz@...nel.org>
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

Hi Marc,

Apologies, this got lost in my mailbox.

On 11/08/2022 10:49, Marc Zyngier wrote:
> 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?

I am not very sure about this.

Is it possible for a pending interrupt to arrive just after the timer 
has been disabled ?

- Ayan

>
> 	M.
>