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

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Date:   Thu, 30 May 2019 17:57:30 +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 17:30, Richard Cochran <richardcochran@...il.com> wrote:
>
> On Thu, May 30, 2019 at 12:01:23PM +0300, Vladimir Oltean wrote:
> > In fact that's why it doesn't work: because linuxptp adds ptp_dst_mac
> > (01-1B-19-00-00-00) and (01-80-C2-00-00-0E) to the MAC's multicast
> > filter, but the switch in its great wisdom mangles bytes
> > 01-1B-19-xx-xx-00 of the DMAC to place the switch id and source port
> > there (a rudimentary tagging mechanism). So the frames are no longer
> > accepted by this multicast MAC filter on the DSA master port unless
> > it's put in ALLMULTI or PROMISC.
>
> IOW, it is not linuxptp's choice to use these modes, but rather this
> is caused by a limitation of your device.
>

Didn't want to suggest otherwise. I'll see how I'm going to address that.

> > If the meta frames weren't associated with the correct link-local
> > frame, then the whole expect_meta -> SJA1105_STATE_META_ARRIVED
> > mechanism would go haywire, but it doesn't.
>
> 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.
The RX and TX timestamps *are* monotonically increasing with time for
all frames when I'm printing them in the {rx,tx}tstamp callbacks.

> > I was actually thinking it has something to do with the fact that I
> > shouldn't apply frequency corrections on timestamps of PTP delay
> > messages. Does that make any sense?
>
> What do you mean by that?  Is the driver altering PTP message fields?

No.
The driver returns free-running timestamps altered with a timecounter
frequency set by adjfine and offset set by adjtime.
I was wondering out loud if there's any value in identifying delay
messages in order to not apply this frequency adjustment for their
timestamps.

-Vladimir

>
> Thanks,
> Richard