linux-kernel - Re: [patch 8/8] ntp: Consolidate the RTC update implementation

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Message-ID: <20201207210505.GM5487@ziepe.ca>
Date:   Mon, 7 Dec 2020 17:05:05 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Miroslav Lichvar <mlichvar@...hat.com>,
        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 8/8] ntp: Consolidate the RTC update implementation

On Sun, Dec 06, 2020 at 10:46:21PM +0100, Thomas Gleixner wrote:
>  /*
>   * If we have an externally synchronized Linux clock, then update RTC clock
>   * accordingly every ~11 minutes. Generally RTCs can only store second
> @@ -686,6 +621,10 @@ static bool sync_cmos_clock(void)
>   */
>  static void sync_hw_clock(struct work_struct *work)
>  {
> +	static unsigned long offset_nsec = NSEC_PER_SEC / 2;

A comment here explaining this is the default: because the platform is
assumed to use CMOS, and by the way, this whole thing is obsolete
don't use it, seems appropriate..

The time split is clearer if you think of it from a bus/datasheet
perspective, less clear if you try to measure the system directly, eg
from an alarm. But, I think this  has a better chance of some rtclib
driver authors to fill in the datasheet value at least.

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason