linux-kernel - Re: [PATCH net-next v1 2/4] net: phy: micrel: lan8841: set default PTP latency values

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Date: Tue, 23 Apr 2024 23:10:09 -0700
From: Richard Cochran <richardcochran@...il.com>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Andrew Lunn <andrew@...n.ch>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Jose Abreu <joabreu@...opsys.com>,
	"David S. Miller" <davem@...emloft.net>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Woojung Huh <woojung.huh@...rochip.com>,
	Arun Ramadoss <arun.ramadoss@...rochip.com>,
	Russell King <linux@...linux.org.uk>, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	UNGLinuxDriver@...rochip.com,
	linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH net-next v1 2/4] net: phy: micrel: lan8841: set default
 PTP latency values

On Tue, Apr 23, 2024 at 09:07:59AM +0200, Oleksij Rempel wrote:

> Are the recommended FOSS projects managing calibration values per-
> linkmode/port/device in user space?

No, I haven't seen this.  I think the vendors should provide the
numbers, like in the data sheet.  This is more useful and flexible
than letting vendors hard code the numbers into the source code of
device drivers.

> What is recommended way for calibration? Using some recommended device?

You can try the "Calibration procedures" in IEEE 1588-2019, Annex N.

Or if you have end to end PPS outputs (from the GM server and the
client) then you can simply compare them with an oscilloscope and
correct any static offset with the ptp4l "delayAsymmetry"
configuration option.

Or if you have auxiliary event inputs on both server and client, feed
a pulse generator into both, compare time stamps, etc.

Also linuxptp supports Meinberg's NetSync Monitor method.

Also there are commercial vendors that rent/sell test equipment for
PTP networks.

So there are many possibilities.

HTH,
Richard