Subject: Re: [PATCH 1/2] clocksource/drivers/timer-ti-dm: Prepare to handle dra7 timer wrap issue

From: Tony Lindgren <[email-masked]>
Date: Tue, 23 Mar 2021 08:31:51 +0200

* Daniel Lezcano <[email-masked]> [210322 18:24]:
> On 22/03/2021 17:33, Tony Lindgren wrote:
> > Hi,
> > 
> > * Daniel Lezcano <[email-masked]> [210322 15:56]:
> >> On 04/03/2021 08:37, Tony Lindgren wrote:
> >>> There is a timer wrap issue on dra7 for the ARM architected timer.
> >>> In a typical clock configuration the timer fails to wrap after 388 days.
> >>>
> >>> To work around the issue, we need to use timer-ti-dm timers instead.
> >>>
> >>> Let's prepare for adding support for percpu timers by adding a common
> >>> dmtimer_clkevt_init_common() and call it from dmtimer_clockevent_init().
> >>> This patch makes no intentional functional changes.
> >>>
> >>> Signed-off-by: Tony Lindgren <[email-masked]>
> >>> ---
> >>
> >> [ ... ]
> >>
> >>> @@ -575,33 +574,60 @@ static int __init dmtimer_clockevent_init(struct device_node *np)
> >>>  	 */
> >>>  	writel_relaxed(OMAP_TIMER_CTRL_POSTED, t->base + t->ifctrl);
> >>>  
> >>> +	if (dev->cpumask == cpu_possible_mask)
> >>> +		irqflags = IRQF_TIMER;
> >>> +	else
> >>> +		irqflags = IRQF_TIMER | IRQF_NOBALANCING;
> >>
> >> Can you explain the reasoning behind the test above ?
> > 
> > In the per cpu case we assign one dmtimer per cpu, and we want the
> > interrupt handling on the assigned CPU. In the per cpu case we have
> > the cpu specified with dev->cpumask unlike for the normal clockevent
> > case.
> > 
> > In the per cpu dmtimer case the interrupt line is not wired per cpu
> > though, so I don't think we want to add IRQF_PERCPU here.
> 
> If it is per cpu, then the parameter will be cpumask_of(cpu). If there
> is one cpu, no balancing can happen and then the IRQF_NOBALANCING is not
> needed, neither this test and the irqflags, right?

Oh yeah you're right, none of that is needed. For the percpu case we
already have irq_force_affinity() in omap_dmtimer_starting_cpu(). I'll
update and send out v2 of these two patches.

Thanks,

Tony

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