netdev - Re: [PATCH net-next 1/3] ptp: Allow reassigning calibration pin function

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Message-ID: <20140626145720.GB10999@netboy>
Date:	Thu, 26 Jun 2014 16:57:20 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	Christian Riesch <christian.riesch@...cron.at>
Cc:	Stefan Sørensen 
	<stefan.sorensen@...ctralink.com>,
	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 1/3] ptp: Allow reassigning calibration pin
 function

On Thu, Jun 26, 2014 at 08:14:58AM +0200, Christian Riesch wrote:
> On Thu, Jun 26, 2014 at 7:21 AM, Richard Cochran <richardcochran@...il.com> wrote:
> > Reassigning the calibration function never makes sense, because it is
> > only used in the driver probe method.
> 
> Yes, indeed, but isn't that a bug? I think the calibration should be
> done again whenever the clock is loaded with a new value, i.e. in
> ptp_dp83640_settime. See section 3.1 in [1]: "All subsequent settings
> should use a step
> adjustment or temporary rate adjustment, which should occur at each
> PHY without introducing any error." This means, whenever we do
> something else (directly write to the clock register), we must
> recalibrate.

When we write the time, we use the broadcast address, and so the PHYs
receive the data at exactly the same time on the MDIO bus. But maybe
they would still need a new, fine calibration. Can you test this?

(I don't have a board with two phys.)

Thanks,
Richard
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