linux-kernel - Re: dmtimer: ack pending interrupt during suspend on am335x/am437x?

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Date:   Tue, 10 May 2022 09:19:51 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Drew Fustini <dfustini@...libre.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Dave Gerlach <d-gerlach@...com>, linux-omap@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: dmtimer: ack pending interrupt during suspend on am335x/am437x?

On 2022-05-10 07:49, Tony Lindgren wrote:
> * Drew Fustini <dfustini@...libre.com> [220509 05:07]:
>> Hello Daniel, Tony suggested I mail you along with the list to get
>> feedback. I'm attempting to upstream these two patches [1][2] from
>> ti-linux-5.4.y for arch/arm/mach-omap2/timer.c:
>> 96f4c6e2ba8a ("ARM: OMAP2+: timer: Ack pending interrupt during 
>> suspend")
>> 7ae7dd5f8272 ("ARM: OMAP2+: timer: Extend pending interrupt ACK for 
>> gic")
>> 
>> On the TI AM335x and AM437x SoCs, it is possible for a late interrupt 
>> to
>> be generated which will cause a suspend failure. The first patch makes
>> omap_clkevt_idle() ack the irq both in the timer peripheral register
>> and in the interrupt controller to avoid the issue.
>> 
>> On AM437x only, the GIC cannot be directly acked using only the 
>> irqchip
>> calls. To workaround that, the second patch maps the GIC_CPU_BASE and
>> reads the GIC_CPU_INTACK register before calling irq_eoi to properly 
>> ack
>> the late timer interrupts that show up during suspend.
>> 
>> However, Tony removed most of arch/arm/mach-omap2/timer.c with:
>> 2ee04b88547a ("ARM: OMAP2+: Drop old timer code for dmtimer and 32k 
>> counter")
>> 
>> The timers are now implemented in drivers/clocksource/timer-ti-dm.c 
>> and
>> drivers/clocksource/timer-ti-dm-systimer.c. The function
>> dmtimer_clocksource_suspend() disables the dmtimer and clock but does
>> not ack any interrupts.
>> 
>> Tony suggested the right place to ack the interrupt during suspend is
>> in CPU_CLUSTER_PM_ENTER inside omap_timer_context_notifier().
>> 
>> Do you think that would be an acceptable approach?
> 
> Based on what we chatted on irc yesterday, I'd suggest try resetting 
> the
> clockevent on suspend first for am3/4 at omap_clockevent_idle() and see 
> if
> that takes care of the issue. If it's the timer hardware blocking the
> deeper idle states, this should work, and GIC will lose it's context
> on system suspend anyways.

Maybe, but the core tracking code will still know it is in the
middle of an interrupt. I´d expect things like lockdep to shout
at you...

         M.