netdev - Re: [PATCH] fec: Restart PPS after link state change

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Message-ID: <YvRjzwMsMWv3AG1H@lunn.ch>
Date:   Thu, 11 Aug 2022 04:05:03 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Richard Cochran <richardcochran@...il.com>
Cc:     Csókás Bence <csokas.bence@...lan.hu>,
        netdev@...r.kernel.org, Fugang Duan <fugang.duan@....com>
Subject: Re: [PATCH] fec: Restart PPS after link state change

On Wed, Aug 10, 2022 at 06:37:19PM -0700, Richard Cochran wrote:
> On Thu, Aug 11, 2022 at 02:05:39AM +0200, Andrew Lunn wrote:
> > > Yes. We use PPS to synchronize devices on a common backplane. We use PTP to
> > > sync this PPS to a master clock. But if PTP sync drops out, we wouldn't want
> > > the backplane-level synchronization to fail. The PPS needs to stay on as
> > > long as userspace *explicitly* disables it, regardless of what happens to
> > > the link.
> > 
> > We need the PTP Maintainers view on that. I don't know if that is
> > normal or not.
> 
> IMO the least surprising behavior is that once enabled, a feature
> stays on until explicitly disabled.

O.K, thanks for the response.

Your answer is a bit surprising to me. To me, an interface which is
administratively down is completely inactive. The action to down it
should disable everything.

So your answer also implies PPS can be used before the interface is
set administratively up?

	Andrew