linux-kernel - Re: [PATCH 1/7] rtc: Add support for limited alarm timer offsets

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Message-ID: <9b6c7803-f258-472d-9983-530e42e80816@roeck-us.net>
Date:   Wed, 16 Aug 2023 08:24:39 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        Benson Leung <bleung@...omium.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <jstultz@...gle.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Brian Norris <briannorris@...omium.org>
Subject: Re: [PATCH 1/7] rtc: Add support for limited alarm timer offsets

On Wed, Aug 16, 2023 at 04:57:30PM +0200, Alexandre Belloni wrote:
> On 16/08/2023 06:39:30-0700, Guenter Roeck wrote:
> > Some alarm timers are based on time offsets, not on absolute times.
> > In some situations, the amount of time that can be scheduled in the
> > future is limited. This may result in a refusal to suspend the system,
> > causing substantial battery drain.
> > 
> > Some RTC alarm drivers remedy the situation by setting the alarm time
> > to the maximum supported time if a request for an out-of-range timeout
> > is made. This is not really desirable since it may result in unexpected
> > early wakeups.
> > 
> > To reduce the impact of this problem, let RTC drivers report the maximum
> > supported alarm timer offset. The code setting alarm timers can then
> > decide if it wants to reject setting alarm timers to a larger value, if it
> > wants to implement recurring alarms until the actually requested alarm
> > time is met, or if it wants to accept the limited alarm time.
> > 
> > Only introduce the necessary variable into struct rtc_device.
> > Code to set and use the variable will follow with subsequent patches.
> > 
> > Cc: Brian Norris <briannorris@...omium.org>
> > Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> > ---
> >  include/linux/rtc.h | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/include/linux/rtc.h b/include/linux/rtc.h
> > index 1fd9c6a21ebe..b6d000ab1e5e 100644
> > --- a/include/linux/rtc.h
> > +++ b/include/linux/rtc.h
> > @@ -146,6 +146,7 @@ struct rtc_device {
> >  
> >  	time64_t range_min;
> >  	timeu64_t range_max;
> > +	timeu64_t range_max_offset;
> 
> While range_min and range_max are for the wall clock time, I would
> prefer using a name that would clearly mark this as an alarm related
> variable.

Sure, no problem. Do you have a suggestion ? alarm_range_max or
alarm_range_max_offset, maybe ? I'd also be happy to use some other
term for 'offset' if you have a suggestion.

Thanks,
Guenter