Subject: [rtc-linux] Re: [PATCH v4 0/4] pm: Add power off control

From: [email-masked] (Ezequiel Garcia)
Date: Tue, 26 Nov 2013 10:22:46 -0300

On Sat, Nov 23, 2013 at 12:23:35PM -0500, Vaibhav Bedia wrote:
> On Fri, Nov 22, 2013 at 2:50 PM, Ezequiel Garcia
> <[email-masked]> wrote:
> [...]
> >
> > And why specifically *2* seconds, instead of *1* or *33* ?
> >
> > Sounds a bit like voodoo magic on this side :-)
> 
> Consider the scenario where the actual time is 00:00:01.95 secs.
> Due to the 1 second resolution of the RTC, reading the registers
> would return 00:00:01. By the time we get to updating the
> RTC register for the shutdown by adding 1 sec (theoretically the
> smallest delta) we could end up programming the time that's already
> passed and in such cases the system will never shut down.
> 
> 2 secs is the smallest delay that we can use to get the system
> to shutdown reliably.
> 
> So it's not voodoo magic after all ;)
> 

Right, thanks for the details.

Care to add the above explanation to a comment inside the driver?

That way, people won't ask this same question again :-)
-- 
Ezequiel Garc?a, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com