From: Miroslav Lichvar <mlichvar@redhat.com>
To: Andrew Lunn <andrew@lunn.ch>
Cc: Hubert Feurstein <h.feurstein@gmail.com>,
netdev <netdev@vger.kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Richard Cochran <richardcochran@gmail.com>,
Florian Fainelli <f.fainelli@gmail.com>,
Heiner Kallweit <hkallweit1@gmail.com>,
Vladimir Oltean <olteanv@gmail.com>,
"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH net-next v3 2/4] net: mdio: add PTP offset compensation to mdiobus_write_sts
Date: Tue, 20 Aug 2019 17:40:05 +0200 [thread overview]
Message-ID: <20190820154005.GM891@localhost> (raw)
In-Reply-To: <20190820152306.GJ29991@lunn.ch>
On Tue, Aug 20, 2019 at 05:23:06PM +0200, Andrew Lunn wrote:
> > - take a second "post" system timestamp after the completion
>
> For this hardware, completion is an interrupt, which has a lot of
> jitter on it. But this hardware is odd, in that it uses an
> interrupt. Every other MDIO bus controller uses polled IO, with an
> mdelay(10) or similar between each poll. So the jitter is going to be
> much larger.
I think a large jitter is ok in this case. We just need to timestamp
something that we know for sure happened after the PHC timestamp. It
should have no impact on the offset and its stability, just the
reported delay. A test with phc2sys should be able to confirm that.
phc2sys selects the measurement with the shortest delay, which has
least uncertainty. I'd say that applies to both interrupt and polling.
If it is difficult to specify the minimum interrupt delay, I'd still
prefer an overly pessimistic interval assuming a zero delay.
--
Miroslav Lichvar
next prev parent reply other threads:[~2019-08-20 15:40 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-20 8:48 [PATCH net-next v3 0/4] Improve phc2sys precision for mv88e6xxx switch in combination with imx6-fec Hubert Feurstein
2019-08-20 8:48 ` [PATCH net-next v3 1/4] net: mdio: add support for passing a PTP system timestamp to the mii_bus driver Hubert Feurstein
2019-08-20 8:48 ` [PATCH net-next v3 2/4] net: mdio: add PTP offset compensation to mdiobus_write_sts Hubert Feurstein
2019-08-20 9:49 ` Miroslav Lichvar
2019-08-20 12:29 ` Hubert Feurstein
2019-08-20 14:25 ` Miroslav Lichvar
2019-08-20 15:23 ` Andrew Lunn
2019-08-20 15:40 ` Miroslav Lichvar [this message]
2019-08-20 16:56 ` Hubert Feurstein
2019-08-21 8:07 ` Miroslav Lichvar
2019-08-21 9:53 ` Hubert Feurstein
2019-08-21 10:19 ` Vladimir Oltean
2019-08-21 10:19 ` Miroslav Lichvar
2019-08-20 13:26 ` Andrew Lunn
2019-08-20 8:48 ` [PATCH net-next v3 3/4] net: dsa: mv88e6xxx: extend PTP gettime function to read system clock Hubert Feurstein
2019-08-20 8:48 ` [PATCH net-next v3 4/4] net: fec: add support for PTP system timestamping for MDIO devices Hubert Feurstein
2019-08-21 10:28 ` Vladimir Oltean
2019-08-22 3:49 ` [PATCH net-next v3 0/4] Improve phc2sys precision for mv88e6xxx switch in combination with imx6-fec David Miller
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