linux-kernel - Re: [PATCH] rtc: adapt allowed RTC update error

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Message-ID: <20201203155249.GT5487@ziepe.ca>
Date:   Thu, 3 Dec 2020 11:52:49 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Miroslav Lichvar <mlichvar@...hat.com>,
        linux-kernel@...r.kernel.org, John Stultz <john.stultz@...aro.org>,
        Prarit Bhargava <prarit@...hat.com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        linux-rtc@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] rtc: adapt allowed RTC update error

On Thu, Dec 03, 2020 at 03:10:47AM +0100, Alexandre Belloni wrote:

> IIRC, used in conjunction with rtc_hctosys which also adds
> inconditionnaly 500ms this can ends up with the system time
> being one second away from the wall clock time which NTP will take quite
> some time to remove.

I can't remember the details, but this was not the intention. 

As long as systohc and hctosys exist then the design goal of rtclib
should be to provide sub-second accuracy on the round trip of time
through the RTC.

Otherwise what is the point?

Jason