linux-kernel - Re: [PATCH 2/3] ntp: add ADJ

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Date:	Tue, 04 Jan 2011 11:08:31 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	"Kuwahara,T." <6vvetjsrt26xsrzlh1z0zn4d2grdah@...il.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Richard Cochran <richard.cochran@...cron.at>
Subject: Re: [PATCH 2/3] ntp: add ADJ_SETOFFSET mode bit

On Tue, 2011-01-04 at 09:37 +0100, Richard Cochran wrote:
> On Mon, Jan 03, 2011 at 12:44:26PM -0800, John Stultz wrote:
> > On Wed, 2010-12-29 at 05:47 +0900, Kuwahara,T. wrote:
> > > I came up with this simple solution: "Just use ADJ_OFFSET as usual,
> > > but don't forget to disable the kernel PLL."
> > 
> > Again, this seems to be trying to add new functionality into a corner
> > case of a existing mode.
> > 
> > I don't like this because it makes testing and validating that the code
> > is correct for its uses difficult. Especially given that a number of
> > combinations of modes might be set at once. What happens to freq
> > adjustments done at the same time as an ADJ_OFFSET - STA_PLL?
> 
> Where are the mode bits and their combinations documented, anyhow?
> 
> There are lot of papers on NTP, and I have not read them all, but I
> don't recall having seen a precise and succinct decription of the
> ntp_adjtime interface anywhere.

You can find the original ntp_adjtime description here:
Page 22 of:
http://www.eecis.udel.edu/~mills/database/rfc/rfc1589.txt

This pre-dates the nanotime kernel paper, which added MOD_NANO.

thanks
-john



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