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authorChristopher S. Hall <christopher.s.hall@intel.com>2016-02-22 14:15:25 +0300
committerJohn Stultz <john.stultz@linaro.org>2016-03-04 01:23:43 +0300
commit719f1aa4a67199a3c4c68a03f94e5ec44d9d5f82 (patch)
tree0a6cdf499ae615abf88e8d826e0c63c431f54bdb /Documentation/ptp
parentf9677e0f83080bb4186865868c359e72e1fac1ea (diff)
downloadlinux-719f1aa4a67199a3c4c68a03f94e5ec44d9d5f82.tar.xz
ptp: Add PTP_SYS_OFFSET_PRECISE for driver crosstimestamping
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: Richard Cochran <richardcochran@gmail.com> Signed-off-by: Christopher S. Hall <christopher.s.hall@intel.com> [jstultz: Commit subject tweaks] Signed-off-by: John Stultz <john.stultz@linaro.org>
Diffstat (limited to 'Documentation/ptp')
-rw-r--r--Documentation/ptp/testptp.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/Documentation/ptp/testptp.c b/Documentation/ptp/testptp.c
index 6c6247aaa7b9..d99012f41602 100644
--- a/Documentation/ptp/testptp.c
+++ b/Documentation/ptp/testptp.c
@@ -277,13 +277,15 @@ int main(int argc, char *argv[])
" %d external time stamp channels\n"
" %d programmable periodic signals\n"
" %d pulse per second\n"
- " %d programmable pins\n",
+ " %d programmable pins\n"
+ " %d cross timestamping\n",
caps.max_adj,
caps.n_alarm,
caps.n_ext_ts,
caps.n_per_out,
caps.pps,
- caps.n_pins);
+ caps.n_pins,
+ caps.cross_timestamping);
}
}