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The i225/i226 hardware retries if it receives an inappropriate response from the upstream device. If the device retries too quickly, the root port does not respond. The wait between attempts was reduced from 10us to 1us in commit6b8aa753a9("igc: Decrease PTM short interval from 10 us to 1 us"), which said: With the 10us interval, we were seeing PTM transactions take around 12us. Hardware team suggested this interval could be lowered to 1us which was confirmed with PCIe sniffer. With the 1us interval, PTM dialogs took around 2us. While a 1us short cycle time was thought to be theoretically sufficient, it turns out in practice it is not quite long enough. It is unclear if the problem is in the root port or an issue in i225/i226. Increase the wait from 1us to 4us. Increasing to 2us appeared to work in practice on the setups we have available. A value of 4us was chosen due to the limited hardware available for testing, with a goal of ensuring we wait long enough without overly penalizing the response time when unnecessary. The issue can be reproduced with the following: $ sudo phc2sys -R 1000 -O 0 -i tsn0 -m Note: 1000 Hz (-R 1000) is unrealistically large, but provides a way to quickly reproduce the issue. PHC2SYS exits with: "ioctl PTP_OFFSET_PRECISE: Connection timed out" when the PTM transaction fails Fixes:6b8aa753a9("igc: Decrease PTM short interval from 10 us to 1 us") Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com> Tested-by: Mor Bar-Gabay <morx.bar.gabay@intel.com> Tested-by: Avigail Dahan <avigailx.dahan@intel.com> Signed-off-by: Christopher S M Hall <christopher.s.hall@intel.com> Reviewed-by: Corinna Vinschen <vinschen@redhat.com> Signed-off-by: Jacob Keller <jacob.e.keller@intel.com> Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com> Signed-off-by: Tony Nguyen <anthony.l.nguyen@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 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.