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 <[email protected]>
Cc: Richard Cochran <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Acked-by: Richard Cochran <[email protected]>
Signed-off-by: Christopher S. Hall <[email protected]>
[jstultz: Commit subject tweaks]
Signed-off-by: John Stultz <[email protected]>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/ptp_clock_kernel.h b/include/linux/ptp_clock_kernel.h
index b8b73066d137..6b15e168148a 100644
--- a/include/linux/ptp_clock_kernel.h
+++ b/include/linux/ptp_clock_kernel.h
@@ -38,6 +38,7 @@ struct ptp_clock_request {
 	};
 };
 
+struct system_device_crosststamp;
 /**
  * struct ptp_clock_info - decribes a PTP hardware clock
  *
@@ -67,6 +68,11 @@ struct ptp_clock_request {
  * @gettime64:  Reads the current time from the hardware clock.
  *              parameter ts: Holds the result.
  *
+ * @getcrosststamp:  Reads the current time from the hardware clock and
+ *                   system clock simultaneously.
+ *                   parameter cts: Contains timestamp (device,system) pair,
+ *                   where system time is realtime and monotonic.
+ *
  * @settime64:  Set the current time on the hardware clock.
  *              parameter ts: Time value to set.
  *
@@ -105,6 +111,8 @@ struct ptp_clock_info {
 	int (*adjfreq)(struct ptp_clock_info *ptp, s32 delta);
 	int (*adjtime)(struct ptp_clock_info *ptp, s64 delta);
 	int (*gettime64)(struct ptp_clock_info *ptp, struct timespec64 *ts);
+	int (*getcrosststamp)(struct ptp_clock_info *ptp,
+			      struct system_device_crosststamp *cts);
 	int (*settime64)(struct ptp_clock_info *p, const struct timespec64 *ts);
 	int (*enable)(struct ptp_clock_info *ptp,
 		      struct ptp_clock_request *request, int on);