netdev - Re: [PATCH v3 5/8] net: dsa: hellcreek: Add TAPRIO offloading support

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Message-ID: <875z930x5e.fsf@kurt>
Date:   Fri, 28 Aug 2020 14:31:41 +0200
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     Richard Cochran <richardcochran@...il.com>
Cc:     Vladimir Oltean <olteanv@...il.com>, 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>,
        Kamil Alkhouri <kamil.alkhouri@...offenburg.de>,
        ilias.apalodimas@...aro.org
Subject: Re: [PATCH v3 5/8] net: dsa: hellcreek: Add TAPRIO offloading support

Hi Richard,

On Thu Aug 27 2020, Richard Cochran wrote:
> On Tue, Aug 25, 2020 at 11:55:37AM +0200, Kurt Kanzenbach wrote:
>> 
>> I get your point. But how to do it? We would need a timer based on the
>> PTP clock in the switch.
>
> Can't you use an hrtimer based on CLOCK_MONOTONIC?

When the switch and the Linux machine aren't synchronized, we would
calculate the difference between both systems and could arm the Linux
timer based on CLOCK_MONOTONIC. Given the fact that we eight seconds, it
would *probably* work when the ptp offset adjustments are in that range.

>
> I would expect the driver to work based solely on the device's clock.

Understood.

Thanks,
Kurt

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