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

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Date: Tue, 11 Jun 2024 17:02:44 +0200
From: Csókás Bence <csokas.bence@...lan.hu>
To: Andrew Lunn <andrew@...n.ch>
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

Hi!

On 6/11/24 15:06, Andrew Lunn wrote:
> 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.

Correct. And PTP4Linux is already capable of re-syncing (or at least it 
would be, if it weren't for the ENET controller reset. We still need to 
restore all the values of ATIME, ATCORR etc. registers, but that'll come 
in a future patch, when I figure out how to get out of the locking hell).

> Thanks
> 
> 	Andrew
> 

Bence