linux-kernel - Re: [PATCH v5 2/5] tick: Add freeze timer events

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Date:   Tue, 18 Jul 2017 08:40:35 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "dbasehore ." <dbasehore@...omium.org>
cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Rajneesh Bhardwaj <rajneesh.bhardwaj@...el.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        Len Brown <len.brown@...el.com>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v5 2/5] tick: Add freeze timer events

On Mon, 17 Jul 2017, dbasehore . wrote:
> On Mon, Jul 17, 2017 at 6:33 PM, Rafael J. Wysocki <rafael@...nel.org> wrote:
> I could make a patch to try it out. I would probably add a flag to rtc
> timers to indicate whether it wakes the system (default true). We
> would have to add a sync with the rtc irq and the rtc irqwork. I would
> probably add a rtc_timer_sync function that would flush the rtc irq
> and flush the irqwork. I would call this after the freeze_ops sync
> function since the sci irq needs to finish before syncing with the rtc
> irq. Also, pm_wakeup_irq seems racy with the current implementation of
> s2idle_loop since the RTC irq could be mistakenly set as pm_wakeup_irq
> when something else actually triggered the full wakeup. Fortunately, I
> don't think pm_wakeup_irq is used for anything except debugging, but
> we might change that.

There is another option which you might consider. We can reserve one of the
HPET comparators for that purpose and have a special interrupt handler for
it. Checking the HPET for expiry from the low level code should be trivial.

Thanks,

	tglx