Re: [PATCH 00/51] rtc: stop using rtc deprecated functions

Alexandre Belloni
2017-06-21T08:39:29Z

On 21/06/2017 at 09:51:52 +0200, Pavel Machek wrote:
> Hi!
>
> > > I agree with that but not the android guys. They seem to mandate an RTC
> > > that can store time from 01/01/1970. I don't know much more than that
> > > because they never cared to explain why that was actually necessary
> > > (apart from a laconic "this will result in a bad user experience")
> > >
> > > I think tglx had a plan for offsetting the time at some point so 32-bit
> > > platform can pass 2038 properly.
> >
> > Yes, but there are still quite some issues to solve there:
> >
> > 1) How do you tell the system that it should apply the offset in the
> > first place, i.e at boot time before NTP or any other mechanism can
> > correct it?
>
> I'd not do offset. Instead, I'd select a threshold (perhaps year of
> release of given kernel?) and
>
> if (rtc_time < year_of_release_of_kernel)
> rtc_time += 0x100000000;
>
> Ok, we'll have to move away from "rtc_time == 0 indicates zero", as
> seen in some drivers.
>
> > 2) Deal with creative vendors who have their own idea about the 'start
> > of the epoch'
>
> If someone uses different threshold, well, there will be
> confusion. But only for users that have their rtc set to the past,
> which is quite unusual.
>

Or not, having an RTC set in the past is actually quite common. I'd find
it weird to have a new device boot and be set to a date in the future.

Also note that the threshold or offset thing may seem like a good idea
but fails with many RTCs because of how they handle leap years.

--
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering