netdev - Re: [PATCH net-next 2/3] net: dsa: mv88e6xxx: extend PTP gettime function to read system clock

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Message-ID: <20190819152037.GH15291@lunn.ch>
Date:   Mon, 19 Aug 2019 17:20:37 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Vivien Didelot <vivien.didelot@...il.com>
Cc:     Hubert Feurstein <h.feurstein@...il.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Richard Cochran <richardcochran@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next 2/3] net: dsa: mv88e6xxx: extend PTP gettime
 function to read system clock

On Mon, Aug 19, 2019 at 11:16:39AM -0400, Vivien Didelot wrote:
> On Mon, 19 Aug 2019 15:27:33 +0200, Andrew Lunn <andrew@...n.ch> wrote:
> > > @@ -45,7 +45,8 @@ static int mv88e6xxx_smi_direct_write(struct mv88e6xxx_chip *chip,
> > >  {
> > >  	int ret;
> > >  
> > > -	ret = mdiobus_write_nested(chip->bus, dev, reg, data);
> > > +	ret = mdiobus_write_sts_nested(chip->bus, dev, reg, data,
> > > +				       chip->ptp_sts);
> > >  	if (ret < 0)
> > >  		return ret;
> > >  
> > 
> > Please also make a similar change to mv88e6xxx_smi_indirect_write().
> > The last write in that function should be timestamped.
> > 
> > Vivien, please could you think about these changes with respect to
> > RMU. We probably want to skip the RMU in this case, so we get slow but
> > uniform jitter, vs fast and unpredictable jitter from using the RMU.
> 
> The RMU will have its own mv88e6xxx_bus_ops.

Yes, that is what i was expecting. But for this operation, triggering
a PTP timestamp, we probably want it to fall back to MDIO, which is
much more deterministic.

     Andrew