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The DWMAC1000 supports 2 timestamping configurations to configure how frequency adjustments are made to the ptp_clock, as well as the reported timestamp values. There was a previous attempt at upstreaming support for configuring this mode by Olivier Dautricourt and Julien Beraud a few years back [1] In a nutshell, the timestamping can be either set in fine mode or in coarse mode. In fine mode, which is the default, we use the overflow of an accumulator to trigger frequency adjustments, but by doing so we lose precision on the timetamps that are produced by the timestamping unit. The main drawback is that the sub-second increment value, used to generate timestamps, can't be set to lower than (2 / ptp_clock_freq). The "fine" qualification comes from the frequent frequency adjustments we are able to do, which is perfect for a PTP follower usecase. In Coarse mode, we don't do frequency adjustments based on an accumulator overflow. We can therefore have very fine subsecond increment values, allowing for better timestamping precision. However this mode works best when the ptp clock frequency is adjusted based on an external signal, such as a PPS input produced by a GPS clock. This mode is therefore perfect for a Grand-master usecase. Introduce a driver-specific devlink parameter "ts_coarse" to enable or disable coarse mode, keeping the "fine" mode as a default. This can then be changed with: devlink dev param set <dev> name ts_coarse value true cmode runtime The associated documentation is also added. [1] : https://lore.kernel.org/netdev/20200514102808.31163-1-olivier.dautricourt@orolia.com/ Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com> Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk> Reviewed-by: Kory Maincent <kory.maincent@bootlin.com> Link: https://patch.msgid.link/20251024070720.71174-3-maxime.chevallier@bootlin.com Signed-off-by: Paolo Abeni <pabeni@redhat.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 reStructuredText 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.