linuxptp/SOURCES/linuxptp-externalpps.patch

commit f20e568cb2bf3b0ea6105e5624409f02fb9aa2bc
Author: Miroslav Lichvar <mlichvar@redhat.com>
Date:   Thu Jan 9 15:46:05 2025 +0100

    ts2phc: Add option for external reference in automatic mode.
    
    ts2phc running in the automatic mode assumes that the PPS source is one
    of the PHCs used by ptp4l. That doesn't always have to be the case. Add
    "external_pps" option to use the non-automatic-mode reading of the
    source timestamp and don't mark sink clocks as targets if they are
    synchronized by ptp4l.
    
    The use case is holdover with an externally controlled stabilized clock.
    The clock is synchronized by an external process to the PHC when it's
    synchronized by ptp4l and the PHC is synchronized to the external clock
    by ts2phc when not synchronized by ptp4l. Multiple PHCs can be connected
    to the external clock to make a JBOD boundary clock.
    
    Don't require the PHC that is synchronized by ptp4l to be receiving the
    PPS signal (providing timestamps) to make it possible to switch the PPS
    direction to synchronize the external clock if there is only one
    usable channel.
    
    (This is a RHEL-specific downstream patch using "ts2phc.rh_external_pps"
    name for the option to make it clear it's considered experimental.)
    
    Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>

diff --git a/config.c b/config.c
index cbff976..fedc3a0 100644
--- a/config.c
+++ b/config.c
@@ -368,6 +368,7 @@ struct config_item config_tab[] = {
 	GLOB_ITEM_ENU("time_stamping", TS_HARDWARE, timestamping_enu),
 	PORT_ITEM_INT("transportSpecific", 0, 0, 0x0F),
 	PORT_ITEM_INT("ts2phc.channel", 0, 0, INT_MAX),
+	GLOB_ITEM_INT("ts2phc.rh_external_pps", 0, 0, 1),
 	PORT_ITEM_INT("ts2phc.extts_correction", 0, INT_MIN, INT_MAX),
 	PORT_ITEM_ENU("ts2phc.extts_polarity", PTP_RISING_EDGE, extts_polarity_enu),
 	PORT_ITEM_INT("ts2phc.holdover", 0, 0, INT_MAX),
diff --git a/ts2phc.8 b/ts2phc.8
index f17ed71..d57402c 100644
--- a/ts2phc.8
+++ b/ts2phc.8
@@ -287,6 +287,20 @@ the SERVO_LOCKED_STABLE state. The servo state needs be enabled by the
 \fB-a\fP option and when \fBts2phc.extts_polarity\fP is set to \fIboth\fP.
 The default is 0 (disabled).
 
+.TP
+.B ts2phc.rh_external_pps
+This is a RHEL-specific experimental option which can be renamed,
+removed, or the functionality changed, in a future minor update.
+
+It enables an external reference with the \fB-a\fP option. If set to 1, ts2phc
+will assume the source of the PPS signal is a different clock from the PHCs
+used by ptp4l (configured with the \fBboundary_clock_jbod\fP option). The use
+case is a holdover using an externally controlled stabilized clock, which is
+expected to be synchronized to the PHC that is synchronized by ptp4l, and
+running free when ptp4l is not synchronizing any of the PHCs. Note that it is a
+different holdover than the one enabled by the \fBts2phc.holdover\fP option
+below. The default is 0 (disabled).
+
 .TP
 .B ts2phc.nmea_delay
 Specifies the minimum expected delay of NMEA RMC messages in nanoseconds.
diff --git a/ts2phc.c b/ts2phc.c
index 39d31b6..5448496 100644
--- a/ts2phc.c
+++ b/ts2phc.c
@@ -348,18 +348,26 @@ static void ts2phc_reconfigure(struct ts2phc_private *priv)
 			}
 			num_target_clocks++;
 			break;
-		case PS_UNCALIBRATED:
-			num_ref_clocks++;
-			break;
 		case PS_SLAVE:
 			ref_clk = c;
+			/* Fall through */
+		case PS_UNCALIBRATED:
 			num_ref_clocks++;
+			if (priv->external_pps && c->is_target) {
+				pr_info("unselecting %s for synchronization",
+					c->name);
+				c->is_target = false;
+			}
 			break;
 		default:
 			break;
 		}
 		last = c;
 	}
+	if (priv->external_pps) {
+		pr_info("assuming external reference clock");
+		return;
+	}
 	if (num_target_clocks >= 1 && !ref_clk) {
 		priv->ref_clock = last;
 		priv->ref_clock->is_target = false;
@@ -447,7 +455,7 @@ static void ts2phc_synchronize_clocks(struct ts2phc_private *priv, int autocfg)
 	struct ts2phc_clock *c;
 	int holdover, valid;
 
-	if (autocfg) {
+	if (autocfg && !priv->external_pps) {
 		if (!priv->ref_clock) {
 			pr_debug("no reference clock, skipping");
 			return;
@@ -787,6 +795,8 @@ int main(int argc, char *argv[])
 		return -1;
 	}
 
+	priv.external_pps = config_get_int(cfg, NULL, "ts2phc.rh_external_pps");
+
 	priv.holdover_length = config_get_int(cfg, NULL, "ts2phc.holdover");
 	priv.holdover_start = 0;
 
diff --git a/ts2phc.h b/ts2phc.h
index 5dbde9b..63e6122 100644
--- a/ts2phc.h
+++ b/ts2phc.h
@@ -52,6 +52,7 @@ struct ts2phc_private {
 	struct config *cfg;
 	struct pmc_agent *agent;
 	struct ts2phc_clock *ref_clock;
+	bool external_pps;
 	bool state_changed;
 	LIST_HEAD(port_head, ts2phc_port) ports;
 	LIST_HEAD(clock_head, ts2phc_clock) clocks;
diff --git a/ts2phc_pps_sink.c b/ts2phc_pps_sink.c
index af34e39..9076de9 100644
--- a/ts2phc_pps_sink.c
+++ b/ts2phc_pps_sink.c
@@ -441,6 +441,15 @@ int ts2phc_pps_sink_poll(struct ts2phc_private *priv)
 		all_sinks_have_events = true;
 
 		for (i = 0; i < priv->n_sinks; i++) {
+			/*
+			 * In the external PPS mode don't require non-target
+			 * clocks to be receiving PPS to allow switching the
+			 * PPS direction to synchronize the external clock.
+			 */
+			if (priv->external_pps &&
+			    !polling_array->sink[i]->clock->is_target)
+				continue;
+
 			if (!polling_array->collected_events[i]) {
 				all_sinks_have_events = false;
 				break;