Documentation/networking/timestamping.rst

4 Timestamping  title
24   Same timestamping mechanism as SO_TIMESTAMP, but reports the
45 This socket option enables timestamping of datagrams on the reception
98 requested by a particular socket, such as when receive timestamping is
171   have multiple concurrent timestamping requests outstanding. Packets
198   timestamping applications. SOF_TIMESTAMPING_OPT_ID defines how the
314 The SO_TIMESTAMPING interface supports timestamping of bytes in a
316 entire contents of the buffer has passed a timestamping point. That
495 3. Hardware Timestamping configuration: SIOCSHWTSTAMP and SIOCGHWTSTAMP
576 3.1 Hardware Timestamping Implementation: Device Drivers
612   and hardware timestamping is not possible (SKBTX_IN_PROGRESS not set).
629 user to select which PHC to use for timestamping Ethernet frames. Instead, the
647 switches include a timestamping clock of their own, and have the ability to
648 perform network timestamping on their own MAC, such that path delays only
649 measure wire and PHY propagation latencies. Timestamping DSA switches are
655 By design, PTP timestamping with a DSA switch does not need any special
657 host port also supports PTP timestamping, DSA will take care of intercepting
659 hardware timestamping on it. This is because the SO_TIMESTAMPING API does not
664 timestamping:
667   packets with a hardware TX timestamping request from user space.
668   This is required for two-step timestamping, since the hardware
679   packets in a queue waiting for timestamping and the actual timestamps,
685   One-step TX timestamping do not require packet cloning, since there is
698   (through another RX timestamping FIFO). Deferral on RX is typically
712 A PHY driver that supports PTP timestamping must create a ``struct
716 Since PHYs do not have network interface representations, the timestamping and
719 to each individual MAC driver for PHY timestamping support. This entails:
732   deferral for RX timestamping is necessary.  Again like DSA, it becomes the
746   drivers already perform for software timestamping purposes. Therefore, if a
747   MAC supports software timestamping, it does not need to do anything further
753 These perform the same role as timestamping Ethernet PHYs, save for the fact
755 any PHY even if it doesn't support timestamping. In Linux, they are
771 Any TX timestamping logic, be it a plain MAC driver, a DSA switch driver, a PHY
776 For example, a typical driver design for TX timestamping might be to split the
779 1. "TX": checks whether PTP timestamping has been previously enabled through
800 that PTP timestamping is not enabled for anything other than the outermost PHC,