Hi Richard, > -----Original Message----- > From: Richard Cochran <richardcochran@xxxxxxxxx> > Sent: Friday, March 4, 2022 7:26 PM > To: Andrew Lunn <andrew@xxxxxxx> > Cc: Divya Koppera - I30481 <Divya.Koppera@xxxxxxxxxxxxx>; > netdev@xxxxxxxxxxxxxxx; hkallweit1@xxxxxxxxx; linux@xxxxxxxxxxxxxxx; > davem@xxxxxxxxxxxxx; kuba@xxxxxxxxxx; robh+dt@xxxxxxxxxx; > devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; UNGLinuxDriver > <UNGLinuxDriver@xxxxxxxxxxxxx>; Madhuri Sripada - I34878 > <Madhuri.Sripada@xxxxxxxxxxxxx>; Manohar Puri - I30488 > <Manohar.Puri@xxxxxxxxxxxxx> > 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
