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This patch adds the RR2DCDELAY register to the ethtool registers dump. RR2DCDELAY exists on I210 and I211 Intel Gigabit Ethernet chips and it stands for "Read Request To Data Completion Delay". Here is how this register is described in the I210 datasheet: "This field captures the maximum PCIe split time in 16 ns units, which is the maximum delay between the read request to the first data completion. This is giving an estimation of the PCIe round trip time." In other words, whenever I210 reads from the host memory (e.g., fetches a descriptor from the ring), the chip measures every PCI DMA read transaction and captures the maximum value. So it ends up containing the longest DMA transaction time. This register is very useful for troubleshooting and research purposes. If you are dealing with time-sensitive networks, this register can help you get an idea of your "I210-to-ring" latency. This helps answering questions like "should I have PCIe ASPM enabled?" or "should I enable deep C-states?" on my system. It is safe to read this register at any point, reading it has no effect on the I210 chip functionality. Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com> Tested-by: Aaron Brown <aaron.f.brown@intel.com> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
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.