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From:   Vladimir Oltean <vladimir.oltean@nxp.com>
To:     Richard Cochran <richardcochran@gmail.com>
CC:     Andrew Lunn <andrew@lunn.ch>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        David Miller <davem@davemloft.net>,
        Grygorii Strashko <grygorii.strashko@ti.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Joakim Zhang <qiangqing.zhang@nxp.com>,
        Kurt Kanzenbach <kurt@linutronix.de>,
        Miroslav Lichvar <mlichvar@redhat.com>,
        Russell King <linux@arm.linux.org.uk>
Subject: Re: [PATCH RFC V1 net-next 3/4] net: Let the active time stamping
 layer be selectable.
Thread-Topic: [PATCH RFC V1 net-next 3/4] net: Let the active time stamping
 layer be selectable.
Thread-Index: AQHYAPlHUZ7+aaeSVU6jmUK14JiGzaxsOSsAgAC1gICAAAeKAIAAtFaA
Date:   Fri, 21 Jan 2022 14:50:36 +0000
Message-ID: <20220121145035.z4yv2qsub5mr7ljs@skbuf>
References: <20220103232555.19791-4-richardcochran@gmail.com>
 <20220120164832.xdebp5vykib6h6dp@skbuf> <Yeoqof1onvrcWGNp@lunn.ch>
 <20220121040508.GA7588@hoboy.vegasvil.org>
In-Reply-To: <20220121040508.GA7588@hoboy.vegasvil.org>
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On Thu, Jan 20, 2022 at 08:05:08PM -0800, Richard Cochran wrote:
> On Fri, Jan 21, 2022 at 04:38:09AM +0100, Andrew Lunn wrote:
>=20
> > So in the extreme case, you have 7 time stamps, 3 from MACs and 4 from
> > PHYs!
>=20
> :^)
> =20
> > I doubt we want to support this, is there a valid use case for it?
>=20
> Someday, someone will surely say it is important, but with any luck
> I'll be dead by then...

So as I mentioned earlier, the use case would be hardware performance
testing and diagnosing. You may consider that as not that important, but
this is basically what I had to do for several months, and even wrote
a program for that, that collects packet timestamps at all possible points.
And to your point, the more complex a system is, the more important it
becomes to be able to diagnose it precisely.=