On Wed, Mar 09, 2022 at 02:55:49PM +0000, Russell King (Oracle) wrote: > I think we understand this, and compensating for the delay in the PHY > is quite reasonable, which surely will be a fixed amount irrespective > of the board. The PHY delays are not fixed. They can be variable, even packet to packet. https://www.researchgate.net/publication/260434179_Measurement_of_egress_and_ingress_delays_of_PTP_clocks https://www.researchgate.net/publication/265731050_Experimental_verification_of_the_egress_and_ingress_latency_correction_in_PTP_clocks Some PHYs are well behaved. Some are not. In any case, the linuxptp user space stack supports the standardized method of correcting a system's delay asymmetry. IMO it makes no sense to even try to let kernel device drivers correct these delays. Driver authors will get it wrong, and indeed they have already tried and failed. And when the magic numbers change from one kernel release to another, it only makes the end user's job harder, because they will have to update their scripts to correct the bogus numbers. Thanks, Richard
