netdev - Re: [PATCH net-next v6 4/7] net: dsa: hellcreek: Add support for hardware timestamping

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Message-ID: <87r1qb790w.fsf@kurt>
Date:   Tue, 06 Oct 2020 15:56:31 +0200
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Richard Cochran <richardcochran@...il.com>,
        Kamil Alkhouri <kamil.alkhouri@...offenburg.de>,
        ilias.apalodimas@...aro.org
Subject: Re: [PATCH net-next v6 4/7] net: dsa: hellcreek: Add support for hardware timestamping

On Tue Oct 06 2020, Vladimir Oltean wrote:
> On Tue, Oct 06, 2020 at 03:30:36PM +0200, Kurt Kanzenbach wrote:
>> That's the point. The user (or anybody else) cannot disable hardware
>> stamping, because it is always performed. So, why should it be allowed
>> to disable it even when it cannot be disabled?
>
> Because your driver's user can attach a PTP PHY to your switch port, and
> the network stack doesn't support multiple TX timestamps attached to the
> same skb. They'll want the TX timestamp from the PHY and not from your
> switch.

Yeah, sure. That use case makes sense. What's the problem exactly?

Thanks,
Kurt

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