• 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
    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: default avatarJohn Stultz <john.stultz@linaro.org>