netdev - Re: [PATCH v2] net: fec: Add ECR bit macros, fix FEC_ECR

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Date: Tue, 11 Jun 2024 15:06:51 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Csókás Bence <csokas.bence@...lan.hu>
Cc: imx@...ts.linux.dev, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Wei Fang <wei.fang@....com>,
	Shenwei Wang <shenwei.wang@....com>,
	Clark Wang <xiaoning.wang@....com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Richard Cochran <richardcochran@...il.com>
Subject: Re: [PATCH v2] net: fec: Add ECR bit macros, fix FEC_ECR_EN1588
 being cleared on link-down

On Tue, Jun 11, 2024 at 10:04:39AM +0200, Csókás Bence wrote:
> Hi!
> 
> On 6/10/24 21:13, Andrew Lunn wrote:
> > On Fri, Jun 07, 2024 at 10:18:55AM +0200, Csókás, Bence wrote:
> > > FEC_ECR_EN1588 bit gets cleared after MAC reset in `fec_stop()`, which
> > > makes all 1588 functionality shut down on link-down. However, some
> > > functionality needs to be retained (e.g. PPS) even without link.
> > 
> > I don't know much about PPS. Could you point to some documentation,
> > list email etc, which indicated PPS without link is expected to work.
> > 
> > Please also Cc: Richard Cochran for changes like this.
> > 
> > Thanks
> > 	Andrew
> 
> This is what Richard said two years ago on the now-reverted patch:
> 
> Link: https://lore.kernel.org/netdev/YvRdTwRM4JBc5RuV@hoboy.vegasvil.org

Thanks.

So when you have sync, you have a 1Hz clock, synchronised to the grand
master. When the link is down, or communication with the grand master
is lost, you get a free running clock of around 1Hz. I presume that if
the link does up again and communication to the grand master is
restored, there is a phase shift in the 1Hz clock, and a frequency
correction? The hardware has to cope with this.

> Plus, this patch doesn't even re-enable PPS or any other 1588 functions, it
> just prevents the adapter from forgetting it is even 1588-capable. I'll
> resubmit with more clear wording and appropriate "Fixes:" and "Cc:" tags.

Thanks

	Andrew