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

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Date:   Fri, 31 May 2019 19:16:17 +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 Fri, 31 May 2019 at 19:09, Richard Cochran <richardcochran@...il.com> wrote:
>
> On Fri, May 31, 2019 at 06:23:34PM +0300, Vladimir Oltean wrote:
> > You mean to queue it and subvert DSA's own RX timestamping callback?
>
> No, use the callback.
>
> > Why would I do that? Just so as not to introduce my .can_timestamp
> > callback?
>
> Right, the .can_timestamp is unneeded, AFAICT.
>
> > > Now I'm starting to understand your series.  I think it can be done in
> > > simpler way...
> > >
> > > sja1105_rcv_meta_state_machine - can and should be at the driver level
> > > and not at the port level.
> > >
> >
> > Can: yes. Should: why?
>
> To keep it simple and robust.
>
> > One important aspect makes this need be a little bit more complicated:
> > reconstructing these RX timestamps.
> > You see, there is a mutex on the SPI bus, so in practice I do need the
> > sja1105_port_rxtstamp_work for exactly this purpose - to read the
> > timestamping clock over SPI.
>
> Sure.  But you schedule the work after a META frame.  And no busy
> waiting is needed.

Ok, I suppose this could work.
But now comes the question on what to do on error cases - the meta
frame didn't arrive. Should I just drop the skb waiting for it? Right
now I "goto rcv_anyway" - which linuxptp doesn't like btw.

>
> Thanks,
> Richard