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
172   have multiple concurrent timestamping requests outstanding. Packets
199   timestamping applications. SOF_TIMESTAMPING_OPT_ID defines how the
332 The SO_TIMESTAMPING interface supports timestamping of bytes in a
334 entire contents of the buffer has passed a timestamping point. That
514 3. Hardware Timestamping configuration: SIOCSHWTSTAMP and SIOCGHWTSTAMP
595 3.1 Hardware Timestamping Implementation: Device Drivers
631   and hardware timestamping is not possible (SKBTX_IN_PROGRESS not set).
648 user to select which PHC to use for timestamping Ethernet frames. Instead, the
666 switches include a timestamping clock of their own, and have the ability to
667 perform network timestamping on their own MAC, such that path delays only
668 measure wire and PHY propagation latencies. Timestamping DSA switches are
674 By design, PTP timestamping with a DSA switch does not need any special
676 host port also supports PTP timestamping, DSA will take care of intercepting
678 hardware timestamping on it. This is because the SO_TIMESTAMPING API does not
683 timestamping:
686   packets with a hardware TX timestamping request from user space.
687   This is required for two-step timestamping, since the hardware
698   packets in a queue waiting for timestamping and the actual timestamps,
704   One-step TX timestamping do not require packet cloning, since there is
717   (through another RX timestamping FIFO). Deferral on RX is typically
731 A PHY driver that supports PTP timestamping must create a ``struct
735 Since PHYs do not have network interface representations, the timestamping and
738 to each individual MAC driver for PHY timestamping support. This entails:
751   deferral for RX timestamping is necessary.  Again like DSA, it becomes the
765   drivers already perform for software timestamping purposes. Therefore, if a
766   MAC supports software timestamping, it does not need to do anything further
772 These perform the same role as timestamping Ethernet PHYs, save for the fact
774 any PHY even if it doesn't support timestamping. In Linux, they are
790 Any TX timestamping logic, be it a plain MAC driver, a DSA switch driver, a PHY
795 For example, a typical driver design for TX timestamping might be to split the
798 1. "TX": checks whether PTP timestamping has been previously enabled through
819 that PTP timestamping is not enabled for anything other than the outermost PHC,