On Mon, Nov 09, 2020 at 10:10:19PM -0800, Vinicius Costa Gomes wrote: > i225 has support for PCIe PTM, which allows us to implement support > for the PTP_SYS_OFFSET_PRECISE ioctl(), implemented in the driver via > the getcrosststamp() function. Would it be possible to provide the PTM measurements with the PTP_SYS_OFFSET_EXTENDED ioctl instead of PTP_SYS_OFFSET_PRECISE? As I understand it, PTM is not cross timestamping. It's basically NTP over PCIe, which provides four timestamps with each "dialog". From the other constants added to the header file it looks like they could all be obtained and then they could be converted to the triplets returned by the EXTENDED ioctl. The main advantage would be that it would provide applications with the round trip time, which is important to estimate the maximum error in the measurement. As your example phc2sys output shows, with the PRECISE ioctl the delay is 0, which is misleading here. I suspect the estimate would be valid only when the NIC is connected directly to the PTM root (PCI root complex). Is it possible to get the timestamps or delay from PTM-capable switches on the path between CPU and NIC? Also, how frequent can be the PTM dialogs? Could they be performed synchronously in the ioctl? -- Miroslav Lichvar
