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

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Date:   Mon, 16 Oct 2023 16:50:01 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Köry Maincent <kory.maincent@...tlin.com>
Cc:     Andrew Lunn <andrew@...n.ch>, Jakub Kicinski <kuba@...nel.org>,
        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>,
        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, Oct 16, 2023 at 12:41:34PM +0200, Köry Maincent wrote:

> Still I am wondering why hardware timestamping capabilities can be enabled
> without phc.

There is hardware that simply provides time values on frames from a
free running clock, and that clock cannot be read, set, or adjusted.

So the time stamps only relate to other time stamps from the same
device.  That might be used for performance analysis.

Thanks,
Richard