Re: [PATCH 7/7] rtc: cmos: Add suspend/resume endurance testing hook

[Zhang Rui <rui.zhang@intel.com>]

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.

thanks,
rui

> 
> On 05/05/2022 09:58:14+0800, Zhang Rui wrote:
> > Automated suspend/resume testing uses the RTC for wakeup.
> > A short rtcwake period is desirable, so that more suspend/resume
> > cycles can be completed, while the machine is available for
> > testing.
> > 
> > But if too short a wake interval is specified, the event can occur,
> > while still suspending, and then no event wakes the suspended
> > system
> > until the user notices that testing has stalled, and manually
> > intervenes.
> > 
> > Here we add a hook to the rtc-cmos driver to
> > a) remove the alarm timer in the beginning of suspend, if there is
> > any
> > b) arm the wakeup in PM notifier callback, which is in the very
> > late stage
> >    before the system really suspends
> > The remaining part of suspend is usually measured under 10 ms,
> > and so arming the timer at this point could be as fast as the
> > minimum
> > time of 1-second.
> > 
> > But there is a 2nd race.  The RTC has 1-second granularity, and
> > unless
> > you are timing the timer with a higher resolution timer,
> > there is no telling if the current time + 1 will occur immediately,
> > or a full second in the future.  And so 2-seconds is the safest
> > minimum:
> > 
> > Run 1,000 s2idle cycles with (max of) 2 second wakeup period:
> > 
> >  # echo 2 > /sys/module/rtc_cmos/parameters/rtc_wake_override_sec
> >  # sleepgraph.py -m freeze -multi 1000 0 -skiphtml -gzip
> > 
> > Clear the timer override, to not interfere with subsequent
> > real use of the machine's suspend/resume feature:
> > 
> >  # echo 0 > /sys/module/rtc_cmos/parameters/rtc_wake_override_sec
> > 
> > Originally-by: Len Brown <len.brown@intel.com>
> > Signed-off-by: Zhang Rui <rui.zhang@intel.com>
> > Tested-by: Sumeet Pawnikar <sumeet.r.pawnikar@intel.com>
> > ---
> >  drivers/rtc/interface.c |  1 +
> >  drivers/rtc/rtc-cmos.c  | 45
> > +++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 46 insertions(+)
> > 
> > diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
> > index 9edd662c69ac..fb93aa2dc99c 100644
> > --- a/drivers/rtc/interface.c
> > +++ b/drivers/rtc/interface.c
> > @@ -1020,6 +1020,7 @@ void rtc_timer_cancel(struct rtc_device *rtc,
> > struct rtc_timer *timer)
> >  		rtc_timer_remove(rtc, timer);
> >  	mutex_unlock(&rtc->ops_lock);
> >  }
> > +EXPORT_SYMBOL_GPL(rtc_timer_cancel);
> >  
> >  /**
> >   * rtc_read_offset - Read the amount of rtc offset in parts per
> > billion
> > diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
> > index 7c006c2b125f..9590c40fa9d8 100644
> > --- a/drivers/rtc/rtc-cmos.c
> > +++ b/drivers/rtc/rtc-cmos.c
> > @@ -32,6 +32,7 @@
> >  #include <linux/init.h>
> >  #include <linux/interrupt.h>
> >  #include <linux/spinlock.h>
> > +#include <linux/suspend.h>
> >  #include <linux/platform_device.h>
> >  #include <linux/log2.h>
> >  #include <linux/pm.h>
> > @@ -70,6 +71,9 @@ static inline int cmos_use_acpi_alarm(void)
> >  }
> >  #endif
> >  
> > +static int rtc_wake_override_sec;
> > +module_param(rtc_wake_override_sec, int, 0644);
> > +
> >  struct cmos_rtc {
> >  	struct rtc_device	*rtc;
> >  	struct device		*dev;
> > @@ -89,6 +93,7 @@ struct cmos_rtc {
> >  	u8			century;
> >  
> >  	struct rtc_wkalrm	saved_wkalrm;
> > +	struct notifier_block	pm_nb;
> >  };
> >  
> >  /* both platform and pnp busses use negative numbers for invalid
> > irqs */
> > @@ -744,6 +749,42 @@ static irqreturn_t cmos_interrupt(int irq,
> > void *p)
> >  		return IRQ_NONE;
> >  }
> >  
> > +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;
> > +		if (cmos->wake_on)
> > +			cmos->wake_on(cmos->dev);
> > +		break;
> > +	}
> > +
> > +	return NOTIFY_OK;
> > +}
> > +
> >  #ifdef	CONFIG_PNP
> >  #define	INITSECTION
> >  
> > @@ -937,6 +978,9 @@ cmos_do_probe(struct device *dev, struct
> > resource *ports, int rtc_irq)
> >  		 nvmem_cfg.size,
> >  		 use_hpet_alarm() ? ", hpet irqs" : "");
> >  
> > +	cmos_rtc.pm_nb.notifier_call = cmos_pm_notify;
> > +	register_pm_notifier(&cmos_rtc.pm_nb);
> > +
> >  	return 0;
> >  
> >  cleanup2:
> > @@ -965,6 +1009,7 @@ static void cmos_do_remove(struct device *dev)
> >  	struct cmos_rtc	*cmos = dev_get_drvdata(dev);
> >  	struct resource *ports;
> >  
> > +	unregister_pm_notifier(&cmos_rtc.pm_nb);
> >  	cmos_do_shutdown(cmos->irq);
> >  
> >  	if (is_valid_irq(cmos->irq)) {
> > -- 
> > 2.17.1
> > 
> 
>