linux-kernel - 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.