Re: [PATCH net-next v7 2/3] dpll: zl3073x: add channel ToD, phase step and TIE operations

On 11/08/2026 14:46, Ivan Vecera wrote:

[...]

+ * zl3073x_chan_tod_adjust - atomic ToD read-modify-write with rollover guard
+ * @zldev: pointer to zl3073x device
+ * @ch: DPLL channel index
+ * @delta: time adjustment to apply
+ *
+ * Reads the next-Hz ToD and current ToD, then checks whether enough time
+ * remains before the next 1 Hz rollover to safely complete the write.
+ * Re-reads if the 1 Hz tick crossed between the two reads or if less
+ * than 20 ms remains before the next rollover. Applies @delta and writes
+ * the result back.

you keep 20ms threshold based on the avg read/write transaction time (I
assume), but it may happen, that this call will be preempted in between
reads and write, and 20ms will not be enough before 1Hz rollover. Have
you though about such option?

+ *
+ * Context: Caller must serialize all zl3073x_chan_tod_* calls externally.
+ * Return: 0 on success, <0 on error
+ */
+int zl3073x_chan_tod_adjust(struct zl3073x_dev *zldev, u8 ch,
+			    struct timespec64 delta)
+{
+#define ZL_TOD_MAX_RETRIES	20
+	static const long threshold_ns = 20 * NSEC_PER_MSEC;
+	struct timespec64 ts_next, ts_cur, diff;
+	int rc, i;
+
+	for (i = 0; i < ZL_TOD_MAX_RETRIES; i++) {
+		rc = zl3073x_chan_tod_read(zldev, ch, true, &ts_next, NULL);
+		if (rc)
+			return rc;
+
+		rc = zl3073x_chan_tod_read(zldev, ch, false, &ts_cur, NULL);
+		if (rc)
+			return rc;
+
+		/* Ensure the 1 Hz tick did not cross between the two reads
+		 * and that enough margin remains to complete the write.
+		 */
+		diff = timespec64_sub(ts_next, ts_cur);
+		if (diff.tv_sec > 0 ||
+		    (!diff.tv_sec && diff.tv_nsec >= threshold_ns))
+			break;
+	}
+	if (i == ZL_TOD_MAX_RETRIES) {
+		dev_warn(zldev->dev,
+			 "DPLL%u ToD adjust failed to get stable margin\n",
+			 ch);
+		return -EBUSY;
+	}
+
+	/* Apply delta to the next-Hz ToD */
+	ts_next = timespec64_add(ts_next, delta);
+	if (!timespec64_valid(&ts_next))

maybe timespec64_valid_settod() will be better as the code is about
modifying ToD?

+		return -EINVAL;
+
+	return zl3073x_chan_tod_write(zldev, ch, ts_next);
+#undef ZL_TOD_MAX_RETRIES
+}