361800876f
The PTP_SYS_OFFSET ioctl, which can be used to measure the offset between a PHC and the system clock, includes the total time that the driver needs to read the PHC timestamp. This typically involves reading of multiple PCI registers (sometimes in multiple iterations) and the register that contains the lowest bits of the timestamp is not read in the middle between the two readings of the system clock. This asymmetry causes the measured offset to have a significant error. Introduce a new ioctl, driver function, and helper functions, which allow the reading of the lowest register to be isolated from the other readings in order to reduce the asymmetry. The ioctl returns three timestamps for each measurement: - system time right before reading the lowest bits of the PHC timestamp - PHC time - system time immediately after reading the lowest bits of the PHC timestamp Cc: Richard Cochran <richardcochran@gmail.com> Cc: Jacob Keller <jacob.e.keller@intel.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Miroslav Lichvar <mlichvar@redhat.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.