[PATCH net-next v2 2/6] ptp: add functions to adjust system timestamps

[James Clark <jjc@jclark.com>]

Add ptp_adjust_system_prets() and ptp_adjust_system_postts(), which
shift the pre or post system timestamp by a given CLOCK_MONOTONIC_RAW
duration. The selected clock's time is shifted by the duration scaled by
that clock's current frequency relative to CLOCK_MONOTONIC_RAW, with
ktime_scale_raw_ns().

An MDIO bus driver can take system timestamps around the command that
starts a write, and knows how long after that command the write
completes, so it can shift the timestamps to bound the completion of
the write.

Signed-off-by: James Clark <jjc@jclark.com>
Assisted-by: LLM
---
Changes in v2:
- Scale the shift of the selected clock's time by that clock's current
  frequency relative to CLOCK_MONOTONIC_RAW with ktime_scale_raw_ns(),
  in place of adding the CLOCK_MONOTONIC_RAW duration unscaled
- Move before the mdio core patch (was 3/5), which now uses these
  helpers

 include/linux/ptp_clock_kernel.h | 55 ++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/include/linux/ptp_clock_kernel.h b/include/linux/ptp_clock_kernel.h
index 36a27a91059..b952744ff69 100644
--- a/include/linux/ptp_clock_kernel.h
+++ b/include/linux/ptp_clock_kernel.h
@@ -520,4 +520,59 @@ static inline void ptp_read_system_postts(struct ptp_system_timestamp *sts)
 		ktime_get_snapshot_id(sts->clockid, &sts->post_sts);
 }
 
+static inline void __ptp_adjust_snapshot(clockid_t clockid,
+					 struct system_time_snapshot *snap,
+					 s64 ns)
+{
+	s64 sys_ns;
+
+	if (!snap->valid)
+		return;
+	if (ns < 0)
+		sys_ns = -(s64)ktime_scale_raw_ns(clockid, -ns);
+	else
+		sys_ns = ktime_scale_raw_ns(clockid, ns);
+	snap->systime = ktime_add_ns(snap->systime, sys_ns);
+	snap->monoraw = ktime_add_ns(snap->monoraw, ns);
+	/* No counter value corresponds to the adjusted times. */
+	snap->cycles = 0;
+	snap->cs_id = CSID_GENERIC;
+	snap->hw_cycles = 0;
+	snap->hw_csid = CSID_GENERIC;
+}
+
+/**
+ * ptp_adjust_system_prets - Shift the lower system timestamp bound
+ * @sts: system timestamps, or NULL
+ * @ns: CLOCK_MONOTONIC_RAW nanoseconds to add
+ *
+ * Add @ns to the CLOCK_MONOTONIC_RAW time of the lower bound, and @ns
+ * scaled by the selected clock's current frequency relative to
+ * CLOCK_MONOTONIC_RAW to its time, and clear its clocksource counter
+ * values.
+ */
+static inline void ptp_adjust_system_prets(struct ptp_system_timestamp *sts,
+					   s64 ns)
+{
+	if (sts)
+		__ptp_adjust_snapshot(sts->clockid, &sts->pre_sts, ns);
+}
+
+/**
+ * ptp_adjust_system_postts - Shift the upper system timestamp bound
+ * @sts: system timestamps, or NULL
+ * @ns: CLOCK_MONOTONIC_RAW nanoseconds to add
+ *
+ * Add @ns to the CLOCK_MONOTONIC_RAW time of the upper bound, and @ns
+ * scaled by the selected clock's current frequency relative to
+ * CLOCK_MONOTONIC_RAW to its time, and clear its clocksource counter
+ * values.
+ */
+static inline void ptp_adjust_system_postts(struct ptp_system_timestamp *sts,
+					    s64 ns)
+{
+	if (sts)
+		__ptp_adjust_snapshot(sts->clockid, &sts->post_sts, ns);
+}
+
 #endif
-- 
2.56.0