From: Richard Cochran <richardcochran@gmail.com>
To: Andrew Lunn <andrew@lunn.ch>
Cc: Divya Koppera <Divya.Koppera@microchip.com>,
netdev@vger.kernel.org, hkallweit1@gmail.com,
linux@armlinux.org.uk, davem@davemloft.net, kuba@kernel.org,
robh+dt@kernel.org, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org, UNGLinuxDriver@microchip.com,
madhuri.sripada@microchip.com, manohar.puri@microchip.com
Subject: Re: [PATCH net-next 2/3] dt-bindings: net: micrel: Configure latency values and timestamping check for LAN8814 phy
Date: Fri, 4 Mar 2022 05:55:40 -0800 [thread overview]
Message-ID: <20220304135540.GD16032@hoboy.vegasvil.org> (raw)
In-Reply-To: <YiILJ3tXs9Sba42B@lunn.ch>
On Fri, Mar 04, 2022 at 01:50:47PM +0100, Andrew Lunn wrote:
> Why does this need to be configured, rather than hard coded? Why would
> the latency for a given speed change? I would of thought though you
> would take the average length of a PTP packet and divide is by the
> link speed.
Latency is unrelated to frame length.
My understanding is that it is VERY tricky to measure PHY latency.
Studies have shown that some PHYs vary by link speed, and some vary
randomly, frame by frame.
So I can understand wanting to configure it. However, DTS is probably
the wrong place. The linuxptp user space stack has configuration
variables for this purpose:
egressLatency
Specifies the difference in nanoseconds between the actual
transmission time at the reference plane and the reported trans‐
mit time stamp. This value will be added to egress time stamps
obtained from the hardware. The default is 0.
ingressLatency
Specifies the difference in nanoseconds between the reported re‐
ceive time stamp and the actual reception time at reference
plane. This value will be subtracted from ingress time stamps
obtained from the hardware. The default is 0.
Thanks,
Richard
next prev parent reply other threads:[~2022-03-04 13:55 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-04 9:34 [PATCH net-next 0/3] Add support for 1588 in LAN8814 Divya Koppera
2022-03-04 9:34 ` [PATCH net-next 1/3] net: phy: micrel: Fix concurrent register access Divya Koppera
2022-03-04 9:34 ` [PATCH net-next 2/3] dt-bindings: net: micrel: Configure latency values and timestamping check for LAN8814 phy Divya Koppera
2022-03-04 12:50 ` Andrew Lunn
2022-03-04 13:55 ` Richard Cochran [this message]
2022-03-07 5:02 ` Divya.Koppera
2022-03-07 4:40 ` Divya.Koppera
2022-03-07 13:08 ` Andrew Lunn
2022-03-08 10:05 ` Divya.Koppera
2022-03-08 13:54 ` Andrew Lunn
2022-03-08 14:54 ` Richard Cochran
2022-03-08 15:43 ` Horatiu Vultur
2022-03-08 18:10 ` Andrew Lunn
2022-03-08 22:14 ` Horatiu Vultur
2022-03-08 23:36 ` Andrew Lunn
2022-03-09 1:46 ` Richard Cochran
2022-03-09 1:58 ` Richard Cochran
2022-03-09 13:24 ` Horatiu Vultur
2022-03-09 14:55 ` Russell King (Oracle)
2022-03-09 19:52 ` Richard Cochran
2022-03-11 14:28 ` Horatiu Vultur
2022-03-11 15:08 ` Richard Cochran
2022-03-12 19:36 ` Allan W. Nielsen
2022-03-13 2:41 ` Richard Cochran
2022-03-13 4:04 ` Richard Cochran
2022-03-11 15:21 ` Woojung.Huh
2022-03-12 2:48 ` Richard Cochran
2022-03-12 20:04 ` Andrew Lunn
2022-03-13 2:46 ` Richard Cochran
2022-03-13 15:07 ` Andrew Lunn
2022-03-13 19:37 ` Allan W. Nielsen
2022-03-13 20:03 ` Richard Cochran
2022-03-13 20:07 ` Richard Cochran
2022-03-11 14:07 ` Horatiu Vultur
2022-03-07 21:33 ` Rob Herring
2022-03-04 9:34 ` [PATCH net-next 3/3] net: phy: micrel: 1588 support " Divya Koppera
2022-03-04 13:06 ` Andrew Lunn
2022-03-07 4:58 ` Divya.Koppera
2022-03-07 13:19 ` Andrew Lunn
2022-03-04 13:46 ` Kurt Kanzenbach
2022-03-04 13:57 ` Richard Cochran
2022-03-04 12:50 ` [PATCH net-next 0/3] Add support for 1588 in LAN8814 patchwork-bot+netdevbpf
2022-03-04 13:06 ` Andrew Lunn
2022-03-04 13:21 ` David Miller
2022-03-04 13:47 ` Andrew Lunn
2022-03-04 14:37 ` David Miller
2022-03-04 14:06 ` Richard Cochran
2022-03-04 14:17 ` Andrew Lunn
2022-03-04 15:42 ` Richard Cochran
2022-03-17 12:16 ` Michael Walle
2022-03-17 14:05 ` Allan W. Nielsen
2022-03-17 14:38 ` Andrew Lunn
2022-03-17 19:30 ` Allan W. Nielsen
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