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Date:   Tue, 25 Aug 2020 12:38:30 +0300
From:   Vladimir Oltean <>
To:     Kurt Kanzenbach <>
Cc:     Andrew Lunn <>,
        Vivien Didelot <>,
        Florian Fainelli <>,
        "David S. Miller" <>,
        Jakub Kicinski <>,,
        Rob Herring <>,,
        Sebastian Andrzej Siewior <>,
        Richard Cochran <>,
        Kamil Alkhouri <>,
Subject: Re: [PATCH v3 5/8] net: dsa: hellcreek: Add TAPRIO offloading support

On Tue, Aug 25, 2020 at 11:33:53AM +0200, Kurt Kanzenbach wrote:
> On Tue Aug 25 2020, Vladimir Oltean wrote:
> > On Thu, Aug 20, 2020 at 10:11:15AM +0200, Kurt Kanzenbach wrote:
> >
> > Explain again how this works, please? The hrtimer measures the CLOCK_TAI
> > of the CPU, but you are offloading the CLOCK_TAI domain of the NIC? So
> > you are assuming that the CPU and the NIC PHC are synchronized? What if
> > they aren't?
> Yes, I assume that's synchronized with e.g. phc2sys.

My intuition tells me that this isn't the user's expectation, and that
it should do the right thing even if it's not synchronized to the system

> >
> > And what if the base-time is in the past, do you deal with that (how
> > does the hardware deal with a base-time in the past)?
> > A base-time in the past (example: 0) should work: you should advance the
> > base-time into the nearest future multiple of the cycle-time, to at
> > least preserve phase correctness of the schedule.
> If the hrtimer is programmed with a value in the past, it fires
> instantly.

Yes, it does.

> The callback is executed and the start time is programmed.

With a valid value from the hardware's perspective?


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