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    • Christopher S. Hall's avatar
      ptp: Add PTP_SYS_OFFSET_PRECISE for driver crosstimestamping · 719f1aa4
      Christopher S. Hall authored
      Currently, network /system cross-timestamping is performed in the
      PTP_SYS_OFFSET ioctl. The PTP clock driver reads gettimeofday() and
      the gettime64() callback provided by the driver. The cross-timestamp
      is best effort where the latency between the capture of system time
      (getnstimeofday()) and the device time (driver callback) may be
      significant.
      
      The getcrosststamp() callback and corresponding PTP_SYS_OFFSET_PRECISE
      ioctl allows the driver to perform this device/system correlation when
      for example cross timestamp hardware is available. Modern Intel
      systems can do this for onboard Ethernet controllers using the ART
      counter. There is virtually zero latency between captures of the ART
      and network device clock.
      
      The capabilities ioctl (PTP_CLOCK_GETCAPS), is augmented allowing
      applications to query whether or not drivers implement the
      getcrosststamp callback, providing more precise cross timestamping.
      
      Cc: Prarit Bhargava <prarit@redhat.com>
      Cc: Richard Cochran <richardcochran@gmail.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Andy Lutomirski <luto@amacapital.net>
      Cc: kevin.b.stanton@intel.com
      Cc: kevin.j.clarke@intel.com
      Cc: hpa@zytor.com
      Cc: jeffrey.t.kirsher@intel.com
      Cc: netdev@vger.kernel.org
      Acked-by: default avatarRichard Cochran <richardcochran@gmail.com>
      Signed-off-by: default avatarChristopher S. Hall <christopher.s.hall@intel.com>
      [jstultz: Commit subject tweaks]
      Signed-off-by: John Stultz's avatarJohn Stultz <john.stultz@linaro.org>
      719f1aa4
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