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
496 3. Hardware Timestamping configuration: SIOCSHWTSTAMP and SIOCGHWTSTAMP
577 3.1 Hardware Timestamping Implementation: Device Drivers
613   and hardware timestamping is not possible (SKBTX_IN_PROGRESS not set).
630 user to select which PHC to use for timestamping Ethernet frames. Instead, the
648 switches include a timestamping clock of their own, and have the ability to
649 perform network timestamping on their own MAC, such that path delays only
650 measure wire and PHY propagation latencies. Timestamping DSA switches are
656 By design, PTP timestamping with a DSA switch does not need any special
658 host port also supports PTP timestamping, DSA will take care of intercepting
660 hardware timestamping on it. This is because the SO_TIMESTAMPING API does not
665 timestamping:
668   packets with a hardware TX timestamping request from user space.
669   This is required for two-step timestamping, since the hardware
680   packets in a queue waiting for timestamping and the actual timestamps,
686   One-step TX timestamping do not require packet cloning, since there is
699   (through another RX timestamping FIFO). Deferral on RX is typically
713 A PHY driver that supports PTP timestamping must create a ``struct
717 Since PHYs do not have network interface representations, the timestamping and
720 to each individual MAC driver for PHY timestamping support. This entails:
733   deferral for RX timestamping is necessary.  Again like DSA, it becomes the
747   drivers already perform for software timestamping purposes. Therefore, if a
748   MAC supports software timestamping, it does not need to do anything further
754 These perform the same role as timestamping Ethernet PHYs, save for the fact
756 any PHY even if it doesn't support timestamping. In Linux, they are
772 Any TX timestamping logic, be it a plain MAC driver, a DSA switch driver, a PHY
777 For example, a typical driver design for TX timestamping might be to split the
780 1. "TX": checks whether PTP timestamping has been previously enabled through
801 that PTP timestamping is not enabled for anything other than the outermost PHC,