linux-kernel - Re: [PATCH net-next 0/5] PTP support for the SJA1105 DSA driver

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Date:   Thu, 30 May 2019 18:23:09 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Richard Cochran <richardcochran@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        "David S. Miller" <davem@...emloft.net>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 0/5] PTP support for the SJA1105 DSA driver

On Thu, 30 May 2019 at 18:06, Richard Cochran <richardcochran@...il.com> wrote:
>
> On Thu, May 30, 2019 at 05:57:30PM +0300, Vladimir Oltean wrote:
> > On Thu, 30 May 2019 at 17:30, Richard Cochran <richardcochran@...il.com> wrote:
> > >
> > > Not necessarily.  If two frames that arrive at nearly the same time
> > > get their timestamps mixed up, that would be enough to break the time
> > > values but without breaking your state machine.
> > >
> >
> > This doesn't exactly sound like the type of thing I can check for.
>
> And that is why it cannot work.
>
> > The RX and TX timestamps *are* monotonically increasing with time for
> > all frames when I'm printing them in the {rx,tx}tstamp callbacks.
>
> But are the frames received in the same order?  What happens your MAC
> drops a frame?
>

If it drops a normal frame, it carries on.
If it drops a meta frame, it prints "Expected meta frame", resets the
state machine and carries on.
If it drops a timestampable frame, it prints "Unexpected meta frame",
resets the state machine and carries on.
This doesn't happen under correct runtime conditions though.

-Vladimir

> > The driver returns free-running timestamps altered with a timecounter
> > frequency set by adjfine and offset set by adjtime.
>
> That should be correct.
>
> Thanks,
> Richard