netdev - Re: [PATCH net-next v5 08/16] net: ethtool: Add a command to expose current time stamping layer

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Message-ID: <20231016100313.36d4eab9@kernel.org>
Date: Mon, 16 Oct 2023 10:03:13 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Köry Maincent <kory.maincent@...tlin.com>
Cc: Andrew Lunn <andrew@...n.ch>, Florian Fainelli
 <florian.fainelli@...adcom.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>, "David S . Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
 Jonathan Corbet <corbet@....net>, Jay Vosburgh <j.vosburgh@...il.com>, Andy
 Gospodarek <andy@...yhouse.net>, Nicolas Ferre
 <nicolas.ferre@...rochip.com>, Claudiu Beznea <claudiu.beznea@...on.dev>,
 Horatiu Vultur <horatiu.vultur@...rochip.com>,
 UNGLinuxDriver@...rochip.com, Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>, Heiner Kallweit
 <hkallweit1@...il.com>, Russell King <linux@...linux.org.uk>, Richard
 Cochran <richardcochran@...il.com>, Radu Pirea
 <radu-nicolae.pirea@....nxp.com>, Willem de Bruijn
 <willemdebruijn.kernel@...il.com>, Vladimir Oltean
 <vladimir.oltean@....com>, Michael Walle <michael@...le.cc>, Jacob Keller
 <jacob.e.keller@...el.com>, Maxime Chevallier
 <maxime.chevallier@...tlin.com>
Subject: Re: [PATCH net-next v5 08/16] net: ethtool: Add a command to expose
 current time stamping layer

On Mon, 16 Oct 2023 18:23:07 +0200 Köry Maincent wrote:
> > What's the reason for timestamp precision differences?
> > My understanding so far was the the differences come from:
> >  1. different stamping device (i.e. separate "piece of silicon",
> >     accessed over a different bus, with different PHC etc.)
> >  2. different stamping point (MAC vs DMA)
> > 
> > I don't think any "integrated" device would support stamps which
> > differ under category 1.  
> 
> It was a case reported by Maxime on v3:
> https://lore.kernel.org/netdev/20230324112541.0b3dd38a@pc-7.home/ 

IMHO this talks about how clock control/disciplining works which
is a somewhat independent topic of timestamping.