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For P2P delay measurement, the ingress time stamp of the PDelay_Req is required for the correction field of the PDelay_Resp. The application echoes back the correction field of the PDelay_Req when sending the PDelay_Resp. Some hardware (like the ZHAW InES PTP time stamping IP core) subtracts the ingress timestamp autonomously from the correction field, so that the hardware only needs to add the egress timestamp on tx. Other hardware (like the Microchip KSZ9563) reports the ingress time stamp via an interrupt and requires that the software provides this time stamp via tail-tag on tx. In order to avoid introducing a further application interface for this, the driver can simply emulate the behavior of the InES device and subtract the ingress time stamp in software from the correction field. On egress, the correction field can either be kept as it is (and the time stamp field in the tail-tag is set to zero) or move the value from the correction field back to the tail-tag. Changing the correction field requires updating the UDP checksum (if UDP is used as transport). Signed-off-by: Christian Eggers <ceggers@arri.de> Co-developed-by: Arun Ramadoss <arun.ramadoss@microchip.com> Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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.