[jeffbee]

The bugs I am aware of are on the PCIe side. i225 will lock up the bus if it attempts to do PTM to support PTP. That's a pretty serious bug. You would think Intel has this nailed since they invented PCIe and PCI for that matter. Apparently not. Maybe they outsourced it.

[uep]

This is really interesting for me to read. I encountered a DMA lockup in the hardware by an Ethernet MAC implementation on an ARM chip. It was a Synopsys Designware MAC implementation. It would specifically lockup when PTP was enabled. From my testing, it seemed like it would specifically lockup if some internal queue was overrun. This was speculation on my part, because it would only lockup if I tried to enable timestamping on all packets. It seemed to work alright if the hardware filter was used to only timestamp PTP packets. This can be a significant limitation though, as it can prevent PTP from working with VLANs or DSA switch tags, since the hardware can't identify PTP packets with those extra prefixes.

The PTP timestamps would arrive as a separate DMA transaction after the packet DMA transaction. It very possibly could have been poor integration into the ARM SOC, but your PTP-specific issue on x86 makes me wonder.