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Date:   Sat, 7 May 2022 09:31:26 +0200
From:   Alexandre Belloni <alexandre.belloni@bootlin.com>
To:     Zhang Rui <rui.zhang@intel.com>
Cc:     rjw@rjwysocki.net, kvalo@kernel.org, linux-pm@vger.kernel.org,
        linux-acpi@vger.kernel.org, linux-rtc@vger.kernel.org,
        linux-wireless@vger.kernel.org, daniel.lezcano@linaro.org,
        merez@codeaurora.org, mat.jonczyk@o2.pl,
        sumeet.r.pawnikar@intel.com, len.brown@intel.com
Subject: Re: [PATCH 7/7] rtc: cmos: Add suspend/resume endurance testing hook
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References: <20220505015814.3727692-1-rui.zhang@intel.com>
 <20220505015814.3727692-8-rui.zhang@intel.com>
 <YnWXQE9QASycOzZo@mail.local>
 <320773e042a538782411f4db838bdc70a1b0851b.camel@intel.com>
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On 07/05/2022 10:00:40+0800, Zhang Rui wrote:
> Hi, Alexandre,
> 
> Thanks for reviewing the patch.
> 
> On Fri, 2022-05-06 at 23:46 +0200, Alexandre Belloni wrote:
> > Hello,
> > 
> > I assume I can ignore this patch as this seems to be only for testing
> 
> The main purpose of this patch is for automate testing.
> But this doesn't mean it cannot be part of upstream code, right?
> 
> > I'm not even sure why this is needed as this completely breaks
> > setting
> > the alarm time.
> 
> Or overrides the alarm time, :)
> 
> People rely on the rtc alarm in the automated suspend stress test,
> which suspend and resume the system for over 1000 iterations.
> As I mentioned in the cover letter of this patch series, if the system
> suspend time varies from under 1 second to over 60 seconds, how to
> alarm the RTC before suspend?
> This feature is critical in this scenario.
> 
> Plus, the current solution is transparent to people who don't known/use
> this "rtc_wake_override_sec" parameter. And for people who use this,
> they should know that the previous armed RTC alarm will be overrode
> whenever a system suspend is triggered. I can add a message when the
> parameter is set, if needed.
> 

It is not transparent, if I read your patch properly, this breaks wakeup
for everyone...

> > On 05/05/2022 09:58:14+0800, Zhang Rui wrote:
> > > +static int cmos_pm_notify(struct notifier_block *nb, unsigned long
> > > mode, void *_unused)
> > > +{
> > > +	struct cmos_rtc *cmos = container_of(nb, struct cmos_rtc,
> > > pm_nb);
> > > +	struct rtc_device       *rtc = cmos->rtc;
> > > +	unsigned long           now;
> > > +	struct rtc_wkalrm       alm;
> > > +
> > > +	if (rtc_wake_override_sec == 0)
> > > +		return NOTIFY_OK;
> > > +
> > > +	switch (mode) {
> > > +	case PM_SUSPEND_PREPARE:
> > > +		/*
> > > +		 * Cancel the timer to make sure it won't fire
> > > +		 * before rtc is rearmed later.
> > > +		 */
> > > +		rtc_timer_cancel(rtc, &rtc->aie_timer);
> > > +		break;
> > > +	case PM_SUSPEND_LATE:
> > > +		if (rtc_read_time(rtc, &alm.time))
> > > +			return NOTIFY_BAD;
> > > +
> > > +		now = rtc_tm_to_time64(&alm.time);
> > > +		memset(&alm, 0, sizeof(alm));
> > > +		rtc_time64_to_tm(now + rtc_wake_override_sec,
> > > &alm.time);
> > > +		alm.enabled = true;
> > > +		if (rtc_set_alarm(rtc, &alm))
> > > +			return NOTIFY_BAD;

... because if rtc_wake_override_sec is not set, this sets the alarm to
now which is the current RTC time, ensuring the alarm will never
trigger.


-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com