[channel-monitor] allow configuring startup behavior (#11164)

Allow the Channel Monitor feature to be compiled in but optionally be
disabled by default, allowing it to be started on-demand.

etc/cmake/options.cmake

@@ -183,6 +183,7 @@ ot_option(OT_BORDER_ROUTING_COUNTERS OPENTHREAD_CONFIG_IP6_BR_COUNTERS_ENABLE "b
 ot_option(OT_CHANNEL_MANAGER OPENTHREAD_CONFIG_CHANNEL_MANAGER_ENABLE "channel manager")
 ot_option(OT_CHANNEL_MANAGER_CSL OPENTHREAD_CONFIG_CHANNEL_MANAGER_CSL_CHANNEL_SELECT_ENABLE "channel manager for csl channel")
 ot_option(OT_CHANNEL_MONITOR OPENTHREAD_CONFIG_CHANNEL_MONITOR_ENABLE "channel monitor")
+ot_option(OT_CHANNEL_MONITOR_AUTO_START OPENTHREAD_CONFIG_CHANNEL_MONITOR_AUTO_START_ENABLE "start channel monitor with interface")
 ot_option(OT_COAP OPENTHREAD_CONFIG_COAP_API_ENABLE "coap api")
 ot_option(OT_COAP_BLOCK OPENTHREAD_CONFIG_COAP_BLOCKWISE_TRANSFER_ENABLE "coap block-wise transfer (RFC7959)")
 ot_option(OT_COAP_OBSERVE OPENTHREAD_CONFIG_COAP_OBSERVE_API_ENABLE "coap observe (RFC7641)")

src/core/config/channel_monitor.h

@@ -52,6 +52,20 @@
 #define OPENTHREAD_CONFIG_CHANNEL_MONITOR_ENABLE 0
 #endif
 
+/**
+ * @def OPENTHREAD_CONFIG_CHANNEL_MONITOR_AUTO_START_ENABLE
+ *
+ * Define to 0 to require the Channel Monitor to be manually started.
+ *
+ * If enabled, the Channel Monitor will start and stop automatically when the Thread network interface is brought up
+ * and down.
+ *
+ * Applicable only if Channel Monitoring feature is enabled (i.e., `OPENTHREAD_CONFIG_CHANNEL_MONITOR_ENABLE` is set).
+ */
+#ifndef OPENTHREAD_CONFIG_CHANNEL_MONITOR_AUTO_START_ENABLE
+#define OPENTHREAD_CONFIG_CHANNEL_MONITOR_AUTO_START_ENABLE 1
+#endif
+
 /**
  * @def OPENTHREAD_CONFIG_CHANNEL_MONITOR_SAMPLE_INTERVAL
  *

src/core/thread/thread_netif.cpp

@@ -49,7 +49,7 @@ void ThreadNetif::Up(void)
 
     // Enable the MAC just in case it was disabled while the Interface was down.
     Get<Mac::Mac>().SetEnabled(true);
-#if OPENTHREAD_CONFIG_CHANNEL_MONITOR_ENABLE
+#if OPENTHREAD_CONFIG_CHANNEL_MONITOR_ENABLE && OPENTHREAD_CONFIG_CHANNEL_MONITOR_AUTO_START_ENABLE
     IgnoreError(Get<Utils::ChannelMonitor>().Start());
 #endif
     Get<MeshForwarder>().Start();
@@ -96,7 +96,7 @@ void ThreadNetif::Down(void)
 
     mIsUp = false;
     Get<MeshForwarder>().Stop();
-#if OPENTHREAD_CONFIG_CHANNEL_MONITOR_ENABLE
+#if OPENTHREAD_CONFIG_CHANNEL_MONITOR_ENABLE && OPENTHREAD_CONFIG_CHANNEL_MONITOR_AUTO_START_ENABLE
     IgnoreError(Get<Utils::ChannelMonitor>().Stop());
 #endif
     Get<Notifier>().Signal(kEventThreadNetifStateChanged);