linux-kernel - Re: [PATCH net-next] ptp: add vclock timestamp conversion IOCTL

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Message-ID: <20211013131017.GA20400@hoboy.vegasvil.org>
Date:   Wed, 13 Oct 2021 06:10:17 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Sebastien Laveze <sebastien.laveze@....nxp.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        yangbo.lu@....com, yannick.vignon@....nxp.com,
        rui.sousa@....nxp.com
Subject: Re: [PATCH net-next] ptp: add vclock timestamp conversion IOCTL

On Wed, Oct 13, 2021 at 11:56:00AM +0200, Sebastien Laveze wrote:
> My proposal includes handling PHC offset entirely in software. There is
> no way (and we agree on this :)) to change the PHC offset without
> impacting children virtual clocks.

That means no control over the phase of the output signals.  Super.
 
> Done in software, an offset adjustment has no impact at all on virtual
> clocks (since it can always be done atomically, not RMW).
> 
> So with, no hardware clock phase adjustment and limited frequency
> adjustments, 

But you can't make the end users respect that.  In many cases in the
wild, the GM offset changes suddenly for various reasons, and then the
clients slew at max adjustment.  So there is no expectation of
"limited frequency adjustments."

Thanks,
Richard


> we believe it can be made fully transparent to virtual
> clocks. And that would improve the current limitation of no adjustment
> all, and would unblock the support of features like Qbv for devices
> with a single clock.
> 
> Thanks,
> Sebastien
>