Messages in this thread | | | Date | Wed, 26 Jul 2023 07:50:11 +0200 | From | Marc Kleine-Budde <> | Subject | Re: [PATCH v2] net: stmmac: correct MAC propagation delay |
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On 25.07.2023 20:06:06, Jakub Kicinski wrote: > On Mon, 24 Jul 2023 12:01:31 +0200 Johannes Zink wrote: > > The IEEE1588 Standard specifies that the timestamps of Packets must be > > captured when the PTP message timestamp point (leading edge of first > > octet after the start of frame delimiter) crosses the boundary between > > the node and the network. As the MAC latches the timestamp at an > > internal point, the captured timestamp must be corrected for the > > additional path latency, as described in the publicly available > > datasheet [1]. > > > > This patch only corrects for the MAC-Internal delay, which can be read > > out from the MAC_Ingress_Timestamp_Latency register, since the Phy > > framework currently does not support querying the Phy ingress and egress > > latency. The Closs Domain Crossing Circuits errors as indicated in [1] > > are already being accounted in the stmmac_get_tx_hwtstamp() function and > > are not corrected here. > > > > As the Latency varies for different link speeds and MII > > modes of operation, the correction value needs to be updated on each > > link state change. > > > > As the delay also causes a phase shift in the timestamp counter compared > > to the rest of the network, this correction will also reduce phase error > > when generating PPS outputs from the timestamp counter. > > > > [1] i.MX8MP Reference Manual, rev.1 Section 11.7.2.5.3 "Timestamp > > correction" > > Hi Richard, > > any opinion on this one? > > The subject read to me like it's about *MII clocking delays, I figured > you may have missed it, too.
The patch description clarifies what is being corrected, namely the "MAC-internal delay, which can be read out from the MAC_Ingress_Timestamp_Latency register".
The next step would be to correct PHY latency, but there is no support for querying PHY latency yet.
regards, Marc
-- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung Nürnberg | Phone: +49-5121-206917-129 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-9 | [unhandled content-type:application/pgp-signature] | |