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
180   have multiple concurrent timestamping requests outstanding. Packets
221   timestamping applications. SOF_TIMESTAMPING_OPT_ID defines how the
354 The SO_TIMESTAMPING interface supports timestamping of bytes in a
356 entire contents of the buffer has passed a timestamping point. That
536 3. Hardware Timestamping configuration: ETHTOOL_MSG_TSCONFIG_SET/GET
626 3.1 Hardware Timestamping Implementation: Device Drivers
662   and hardware timestamping is not possible (SKBTX_IN_PROGRESS not set).
679 user to select which PHC to use for timestamping Ethernet frames. Instead, the
697 switches include a timestamping clock of their own, and have the ability to
698 perform network timestamping on their own MAC, such that path delays only
699 measure wire and PHY propagation latencies. Timestamping DSA switches are
705 By design, PTP timestamping with a DSA switch does not need any special
707 host port also supports PTP timestamping, DSA will take care of intercepting
709 hardware timestamping on it. This is because the SO_TIMESTAMPING API does not
714 timestamping:
717   packets with a hardware TX timestamping request from user space.
718   This is required for two-step timestamping, since the hardware
729   packets in a queue waiting for timestamping and the actual timestamps,
735   One-step TX timestamping do not require packet cloning, since there is
748   (through another RX timestamping FIFO). Deferral on RX is typically
762 A PHY driver that supports PTP timestamping must create a ``struct
766 Since PHYs do not have network interface representations, the timestamping and
769 to each individual MAC driver for PHY timestamping support. This entails:
782   deferral for RX timestamping is necessary.  Again like DSA, it becomes the
796   drivers already perform for software timestamping purposes. Therefore, if a
797   MAC supports software timestamping, it does not need to do anything further
803 These perform the same role as timestamping Ethernet PHYs, save for the fact
805 any PHY even if it doesn't support timestamping. In Linux, they are
819 Any TX timestamping logic, be it a plain MAC driver, a DSA switch driver, a PHY
824 For example, a typical driver design for TX timestamping might be to split the
827 1. "TX": checks whether PTP timestamping has been previously enabled through
848 that PTP timestamping is not enabled for anything other than the outermost PHC,