linux-kernel - Re: [PATCH] alarmtimer: implement minimum alarm interval for allowing suspend

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Date:	Thu, 9 Aug 2012 11:31:27 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Todd Poynor <toddpoynor@...gle.com>
Cc:	John Stultz <john.stultz@...aro.org>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, arve@...roid.com
Subject: Re: [PATCH] alarmtimer: implement minimum alarm interval for allowing suspend

On Thursday, August 09, 2012, Todd Poynor wrote:
> alarmtimer suspend return -EBUSY if the next alarm will fire in less
> than 2 seconds.  This allows one RTC seconds tick to occur subsequent
> to this check before the alarm wakeup time is set, ensuring the wakeup
> time is still in the future (assuming the RTC does not tick one more
> second prior to setting the alarm).
> 
> If suspend is rejected due to an imminent alarm, hold a wakeup source
> for 2 seconds to process the alarm prior to reattempting suspend.
> 
> If setting the alarm incurs an -ETIME for an alarm set in the past,
> or any other problem setting the alarm, abort suspend and hold a
> wakelock for 1 second while the alarm is allowed to be serviced or
> other hopefully transient conditions preventing the alarm clear up.
> 
> Signed-off-by: Todd Poynor <toddpoynor@...gle.com>
> ---
>  kernel/time/alarmtimer.c |   18 +++++++++++++-----
>  1 files changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
> index aa27d39..f979d85 100644
> --- a/kernel/time/alarmtimer.c
> +++ b/kernel/time/alarmtimer.c
> @@ -46,6 +46,8 @@ static struct alarm_base {
>  static ktime_t freezer_delta;
>  static DEFINE_SPINLOCK(freezer_delta_lock);
>  
> +static struct wakeup_source *ws;
> +
>  #ifdef CONFIG_RTC_CLASS
>  /* rtc timer and device for setting alarm wakeups at suspend */
>  static struct rtc_timer		rtctimer;
> @@ -250,6 +252,7 @@ static int alarmtimer_suspend(struct device *dev)
>  	unsigned long flags;
>  	struct rtc_device *rtc;
>  	int i;
> +	int ret;
>  
>  	spin_lock_irqsave(&freezer_delta_lock, flags);
>  	min = freezer_delta;
> @@ -279,8 +282,10 @@ static int alarmtimer_suspend(struct device *dev)
>  	if (min.tv64 == 0)
>  		return 0;
>  
> -	/* XXX - Should we enforce a minimum sleep time? */
> -	WARN_ON(min.tv64 < NSEC_PER_SEC);
> +	if (ktime_to_ns(min) < 2 * NSEC_PER_SEC) {
> +		__pm_wakeup_event(ws, 2 * MSEC_PER_SEC);
> +		return -EBUSY;
> +	}
>  
>  	/* Setup an rtc timer to fire that far in the future */
>  	rtc_timer_cancel(rtc, &rtctimer);
> @@ -288,9 +293,11 @@ static int alarmtimer_suspend(struct device *dev)
>  	now = rtc_tm_to_ktime(tm);
>  	now = ktime_add(now, min);
>  
> -	rtc_timer_start(rtc, &rtctimer, now, ktime_set(0, 0));
> -
> -	return 0;
> +	/* Set alarm, if in the past reject suspend briefly to handle */
> +	ret = rtc_timer_start(rtc, &rtctimer, now, ktime_set(0, 0));
> +	if (ret < 0)
> +		__pm_wakeup_event(ws, 1 * MSEC_PER_SEC);

Why not just MSEC_PER_SEC?

> +	return ret;
>  }
>  #else
>  static int alarmtimer_suspend(struct device *dev)
> @@ -821,6 +828,7 @@ static int __init alarmtimer_init(void)
>  		error = PTR_ERR(pdev);
>  		goto out_drv;
>  	}
> +	ws = wakeup_source_register("alarmtimer");
>  	return 0;
>  
>  out_drv:
> 

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