Messages in this thread | | | From | <> | Subject | RE: [PATCH net-next 2/3] dt-bindings: net: micrel: Configure latency values and timestamping check for LAN8814 phy | Date | Mon, 7 Mar 2022 05:02:24 +0000 |
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Hi Richard,
> -----Original Message----- > From: Richard Cochran <richardcochran@gmail.com> > Sent: Friday, March 4, 2022 7:26 PM > To: Andrew Lunn <andrew@lunn.ch> > Cc: Divya Koppera - I30481 <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 > <UNGLinuxDriver@microchip.com>; Madhuri Sripada - I34878 > <Madhuri.Sripada@microchip.com>; Manohar Puri - I30488 > <Manohar.Puri@microchip.com> > Subject: Re: [PATCH net-next 2/3] dt-bindings: net: micrel: Configure latency > values and timestamping check for LAN8814 phy > > EXTERNAL EMAIL: Do not click links or open attachments unless you know the > content is safe > > 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. >
I will check this and come back with fix if it is applicable.
Thanks, Divya
> Thanks, > Richard
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