Hello,
On 23/08/2023 09:50:47-0700, Guenter Roeck wrote:
> Hi Alexandre,
>
> On Thu, Aug 17, 2023 at 03:55:31PM -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@xxxxxxxxxxxx>
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
>
> I guess it is a bit late to get the series into v6.6, but would it be
> possible to apply it to a -next branch to get some more test coverage ?
>
I'm probably going to take 1 and 3-7 for 6.6 once I get a reliable
internet access. I can't take 2/7 without a review or ack from the time
maintainers.
> Either case, do you have any additional comments / feedback ?
>
The main issue that remains is that after 2/7, the rtc_device structure
is not opaque anymore to its user as alarmtimer_suspend now directly
accesses one of the members. But I'd have to find which RTCs have an
absolute limit so we can design a proper API. I may also decide that it
is good enough to require that the alarm range must cover the registered
RTC range.
> Thanks,
> Guenter
>
> > ---
> > v2: Rename range_max_offset -> alarm_offset_max
> >
> > include/linux/rtc.h | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/include/linux/rtc.h b/include/linux/rtc.h
> > index 1fd9c6a21ebe..4c0bcbeb1f00 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 alarm_offset_max;
> > time64_t start_secs;
> > time64_t offset_secs;
> > bool set_start_time;
--
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
