linux-kernel - Re: [PATCH v2 net-next 02/14] dt-bindings: net: add nxp,netc-timer property

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Message-ID: <79e28c65-8dbe-4449-b795-645029c37f88@kernel.org>
Date: Mon, 21 Jul 2025 14:23:45 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Vladimir Oltean <vladimir.oltean@....com>,
 "richardcochran@...il.com" <richardcochran@...il.com>
Cc: Wei Fang <wei.fang@....com>, "robh@...nel.org" <robh@...nel.org>,
 "krzk+dt@...nel.org" <krzk+dt@...nel.org>,
 "conor+dt@...nel.org" <conor+dt@...nel.org>,
 Claudiu Manoil <claudiu.manoil@....com>, Clark Wang <xiaoning.wang@....com>,
 "andrew+netdev@...n.ch" <andrew+netdev@...n.ch>,
 "davem@...emloft.net" <davem@...emloft.net>,
 "edumazet@...gle.com" <edumazet@...gle.com>,
 "kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com"
 <pabeni@...hat.com>, "vadim.fedorenko@...ux.dev"
 <vadim.fedorenko@...ux.dev>, Frank Li <frank.li@....com>,
 "shawnguo@...nel.org" <shawnguo@...nel.org>,
 "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
 "festevam@...il.com" <festevam@...il.com>, "F.S. Peng" <fushi.peng@....com>,
 "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
 "kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: Re: [PATCH v2 net-next 02/14] dt-bindings: net: add nxp,netc-timer
 property

On 18/07/2025 14:01, Vladimir Oltean wrote:
>> Maybe there is another property describing a time provider in the
>> kernel or dtschema. Please look for it. This all looks like you are
>> implementing typical use case in non-typical, but vendor-like, way.
>>
>> Best regards,
>> Krzysztof
> 
> An MII timestamper and a PTP clock (as integrated in a MAC or a PHY) are
> similar but have some notable differences.
> 
> A timestamper is an external device with a free-running counter, which
> sniffs the MII bus between the MAC and the PHY, and provides timestamps
> when the first octet of a packet hits the wire.
> 
> A PTP clock is also a high precision counter, which can be free-running
> or it can be precisely adjusted. It does not have packet timestamping
> capabilities itself, instead the Ethernet MAC can snapshot this counter
> when it places the first octet of a packet on the MII bus. PTP clocks
> frequently have other auxiliary functions, like emitting external
> signals based on the internal time, or snapshotting external signals.
> 
> The timestamper is not required to have these functions. In fact, I am
> looking at ptp_ines.c, the only non-PHY MII timestamper supported by the
> kernel, and I am noting the fact that it does not call ptp_clock_register()
> at all, presumably because it has no controllable PTP clock to speak of.
> 
> That being said, my understanding is based on analyzing the public code
> available to me, and I do not have practical experience with MII bus
> snooping devices, so if Richard could chime in, it would be great.
> 
> I am also in favor of using the "ptp-timer" phandle to describe the link

And it is already used in other binding, so yes, that's the candidate.

> between the MAC and the internal PTP clock that will be snapshot when
> taking packet timestamps. The fman-dtsec.yaml schema also uses it for an
> identical purpose.

Best regards,
Krzysztof