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The switch has the ability to take hardware generated time stamps per port for PTPv2 event messages in Rx and Tx direction. That is useful for achieving needed time synchronization precision for TSN devices/switches. So add support for it. There are two directions: * RX The switch has a single register per port to capture a timestamp. That mechanism is not used due to correlation problems. If the software processing is too slow and a PTPv2 event message is received before the previous one has been processed, false timestamps will be captured. Therefore, the switch can do "inline" timestamping which means it can insert the nanoseconds part of the timestamp directly into the PTPv2 event message. The reserved field (4 bytes) is leveraged for that. This might not be in accordance with (older) PTP standards, but is the only way to get reliable results. * TX In Tx direction there is no correlation problem, because the software and the driver has to ensure that only one event message is "on the fly". However, the switch provides also a mechanism to check whether a timestamp is lost. That can only happen when a timestamp is read and at this point another message is timestamped. So, that lost bit is checked just in case to indicate to the user that the driver or the software is somewhat buggy. Signed-off-by: Kamil Alkhouri <kamil.alkhouri@hs-offenburg.de> Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de> Acked-by: Richard Cochran <richardcochran@gmail.com> Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.