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RGMII requires a delay of 2ns between the data and the clock signal. There are at least three ways this can happen. One possibility is by having the PHY generate this delay. This is a common source for problems (for example with slow TX speeds or packet loss when sending data). The TX delay configuration of the RTL8211F PHY can be set either by pin-strappping the RXD1 pin (HIGH means enabled, LOW means disabled) or through configuring a paged register. The setting from the RXD1 pin is also reflected in the register. Add debug logging to the TX delay configuration on RTL8211F so it's easier to spot these issues (for example if the TX delay is enabled for both, the RTL8211F PHY and the MAC). This is especially helpful because there is no public datasheet for the RTL8211F PHY available with all the RX/TX delay specifics. Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com> Reviewed-by: Florian Fainelli <f.fainelli@gmail.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.