ptp: add PTP_SYS_OFFSET_EXTENDED ioctl

The PTP_SYS_OFFSET ioctl, which can be used to measure the offset
between a PHC and the system clock, includes the total time that the
driver needs to read the PHC timestamp.

This typically involves reading of multiple PCI registers (sometimes in
multiple iterations) and the register that contains the lowest bits of
the timestamp is not read in the middle between the two readings of the
system clock. This asymmetry causes the measured offset to have a
significant error.

Introduce a new ioctl, driver function, and helper functions, which
allow the reading of the lowest register to be isolated from the other
readings in order to reduce the asymmetry. The ioctl returns three
timestamps for each measurement:
- system time right before reading the lowest bits of the PHC timestamp
- PHC time
- system time immediately after reading the lowest bits of the PHC
  timestamp

Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Jacob Keller <jacob.e.keller@intel.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 31 insertions, 0 deletions

diff --git a/include/linux/ptp_clock_kernel.h b/include/linux/ptp_clock_kernel.h
index 51349d124ee5..a1ec0448e341 100644
--- a/include/linux/ptp_clock_kernel.h
+++ b/include/linux/ptp_clock_kernel.h
@@ -39,6 +39,15 @@ struct ptp_clock_request {
 };
 
 struct system_device_crosststamp;
+
+/**
+ * struct ptp_system_timestamp - system time corresponding to a PHC timestamp
+ */
+struct ptp_system_timestamp {
+	struct timespec64 pre_ts;
+	struct timespec64 post_ts;
+};
+
 /**
  * struct ptp_clock_info - decribes a PTP hardware clock
  *
@@ -75,6 +84,14 @@ struct system_device_crosststamp;
  * @gettime64:  Reads the current time from the hardware clock.
  *              parameter ts: Holds the result.
  *
+ * @gettimex64:  Reads the current time from the hardware clock and optionally
+ *               also the system clock.
+ *               parameter ts: Holds the PHC timestamp.
+ *               parameter sts: If not NULL, it holds a pair of timestamps from
+ *               the system clock. The first reading is made right before
+ *               reading the lowest bits of the PHC timestamp and the second
+ *               reading immediately follows that.
+ *
  * @getcrosststamp:  Reads the current time from the hardware clock and
  *                   system clock simultaneously.
  *                   parameter cts: Contains timestamp (device,system) pair,
@@ -124,6 +141,8 @@ 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 (*gettimex64)(struct ptp_clock_info *ptp, struct timespec64 *ts,
+			  struct ptp_system_timestamp *sts);
 	int (*getcrosststamp)(struct ptp_clock_info *ptp,
 			      struct system_device_crosststamp *cts);
 	int (*settime64)(struct ptp_clock_info *p, const struct timespec64 *ts);
@@ -247,4 +266,16 @@ static inline int ptp_schedule_worker(struct ptp_clock *ptp,
 
 #endif
 
+static inline void ptp_read_system_prets(struct ptp_system_timestamp *sts)
+{
+	if (sts)
+		ktime_get_real_ts64(&sts->pre_ts);
+}
+
+static inline void ptp_read_system_postts(struct ptp_system_timestamp *sts)
+{
+	if (sts)
+		ktime_get_real_ts64(&sts->post_ts);
+}
+
 #endif