From 6d10b44bc1a24c5d0decb58c2707a57f328c1a6c Mon Sep 17 00:00:00 2001
From: "Daniel P. Carvalho" <danieloak@gmail.com>
Date: Thu, 17 Sep 2026 17:50:44 -0300
Subject: [PATCH] netutils/ptpd: phase-lock hardware clock via POSIX
 clock_adjtime.

When state->clockid is configured to a hardware PTP clock device
(e.g., /dev/ptp0) instead of CLOCK_REALTIME, ptp_adjtime() previously
passed only the measured frequency drift (-ppb) to clock_adjtime(),
ignoring the residual phase offset (delta_ns / adjustment_ns).
As a result, while the hardware counter tracked frequency, its phase
was never pulled into alignment with the master clock.

Convert delta_ns (which combines frequency drift and current phase error
clamped to max_adjust_ns) to ppb over CONFIG_CLOCK_ADJTIME_PERIOD_MS,
acting as a proportional-integral (PI) phase servo. This drives the
hardware clock to phase lock with the master via POSIX clock_adjtime()
using ADJ_FREQUENCY without requiring proprietary ioctl calls.

Assisted-by: Claude:claude-sonnet-5
Assisted-by: Gemini:gemini-3.8-flash-medium
Signed-off-by: Daniel P. Carvalho <danieloak@gmail.com>
---
 netutils/ptpd/ptpd.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/netutils/ptpd/ptpd.c b/netutils/ptpd/ptpd.c
index 23b2180d5..e8d08c5d3 100644
--- a/netutils/ptpd/ptpd.c
+++ b/netutils/ptpd/ptpd.c
@@ -30,9 +30,10 @@
 #include <stdbool.h>
 #include <stdint.h>
 
-#include <sys/types.h>
 #include <sys/socket.h>
 #include <sys/time.h>
+#include <sys/timex.h>
+#include <sys/types.h>
 
 #include <stdio.h>
 #include <stdlib.h>
@@ -441,9 +442,31 @@ static int ptp_adjtime(FAR struct ptp_state_s *state, int64_t delta_ns,
   else
     {
       struct timex buf;
+      int64_t hw_ppb;
+      const int64_t slew_limit_ppb =
+        CONFIG_CLOCK_ADJTIME_SLEWLIMIT_PPM * 1000;
+
+      /* delta_ns passed here is adjustment_ns, which already
+       * combines frequency drift and current phase error clamped
+       * to max_adjust_ns. Converting it to ppb over
+       * CONFIG_CLOCK_ADJTIME_PERIOD_MS produces the rate needed to
+       * pull the hardware counter into phase lock.
+       */
+
+      hw_ppb = delta_ns * MSEC_PER_SEC /
+               CONFIG_CLOCK_ADJTIME_PERIOD_MS;
+
+      if (hw_ppb > slew_limit_ppb)
+        {
+          hw_ppb = slew_limit_ppb;
+        }
+      else if (hw_ppb < -slew_limit_ppb)
+        {
+          hw_ppb = -slew_limit_ppb;
+        }
 
       memset(&buf, 0, sizeof(buf));
-      buf.freq = (long)(-ppb * 65536 / 1000);
+      buf.freq = hw_ppb * 65536 / 1000;
       buf.modes = ADJ_FREQUENCY;
 
       return clock_adjtime(state->clockid, &buf);