mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-04-20 00:53:50 -04:00
e51bb5c278
The macb PTP support currently implements the `gettime64` callback to allow to retrieve the hardware clock time. Update the implementation to provide the `gettimex64` callback instead. The difference between the two is that with `gettime64` a snapshot of the system clock is taken before and after invoking the callback. Whereas `gettimex64` expects the callback itself to take the snapshots. To get the time from the macb Ethernet core multiple register accesses have to be done. Only one of which will happen at the time reported by the function. This leads to a non-symmetric delay and adds a slight offset between the hardware and system clock time when using the `gettime64` method. This offset can be a few 100 nanoseconds. Switching to the `gettimex64` method allows for a more precise correlation of the hardware and system clocks and results in a lower offset between the two. On a Xilinx ZynqMP system `phc2sys` reports a delay of 1120 ns before and 300 ns after the patch. With the latter being mostly symmetric. Signed-off-by: Lars-Peter Clausen <lars@metafoo.de> Acked-by: Richard Cochran <richardcochran@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.