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According to Synopsis DesignWare EQoS Databook, the Clock Domain Cross synchronization error is introduced tue to the clock(GMII Tx/Rx clock) being different at the capture as compared to the PTP clock(clk_ptp_ref_i) that is used to generate the time. The CDC synchronization error is almost equal to 2 times the clock period of the PTP clock(clk_ptp_ref_i). On a Intel Tigerlake platform (with Marvell 88E2110 external PHY): Before applying this patch (with CDC synchronization error): ptp4l[64.044]: rms 8 max 13 freq +30877 +/- 11 delay 216 +/- 0 ptp4l[65.047]: rms 13 max 20 freq +30869 +/- 17 delay 213 +/- 0 ptp4l[66.050]: rms 12 max 20 freq +30857 +/- 11 delay 213 +/- 0 ptp4l[67.052]: rms 11 max 22 freq +30849 +/- 10 delay 215 +/- 0 ptp4l[68.055]: rms 10 max 16 freq +30853 +/- 13 delay 215 +/- 0 ptp4l[69.057]: rms 7 max 13 freq +30848 +/- 9 delay 216 +/- 0 ptp4l[70.060]: rms 8 max 13 freq +30846 +/- 10 delay 216 +/- 0 ptp4l[71.063]: rms 9 max 15 freq +30836 +/- 8 delay 218 +/- 0 After applying this patch (CDC syncrhonization error is taken care of): ptp4l[61.516]: rms 773 max 824 freq +31526 +/- 158 delay 200 +/- 0 ptp4l[62.519]: rms 427 max 596 freq +31668 +/- 39 delay 198 +/- 0 ptp4l[63.522]: rms 113 max 206 freq +31482 +/- 57 delay 198 +/- 0 ptp4l[64.525]: rms 40 max 56 freq +31316 +/- 29 delay 200 +/- 0 ptp4l[65.528]: rms 47 max 56 freq +31255 +/- 17 delay 200 +/- 0 ptp4l[66.531]: rms 26 max 36 freq +31246 +/- 9 delay 200 +/- 0 ptp4l[67.534]: rms 12 max 18 freq +31254 +/- 12 delay 202 +/- 0 ptp4l[68.537]: rms 7 max 12 freq +31263 +/- 10 delay 202 +/- 0 Signed-off-by: Voon Weifeng <weifeng.voon@intel.com> Signed-off-by: Wong Vee Khee <vee.khee.wong@intel.com> Signed-off-by: David S. Miller <davem@davemloft.net> |
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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.