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

[Ayan Kumar Halder]

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@xxxxxxx> 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@xxxxxxx>
> > ---
> >
> > Please refer to https://lore.kernel.org/all/6cfcd4fa-3afd-1c70-6a70-9df557ee1811@xxxxxxx/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.