[logging] add log level platform handler (#7545)

Adds a log level platform handler that allow platform code to handle
OT log level changes.

include/openthread/instance.h

@@ -53,7 +53,7 @@ extern "C" {
  * @note This number versions both OpenThread platform and user APIs.
  *
  */
-#define OPENTHREAD_API_VERSION (201)
+#define OPENTHREAD_API_VERSION (202)
 
 /**
  * @addtogroup api-instance

include/openthread/platform/logging.h

@@ -161,6 +161,19 @@ typedef enum otLogRegion
  */
 void otPlatLog(otLogLevel aLogLevel, otLogRegion aLogRegion, const char *aFormat, ...);
 
+/**
+ * This function handles OpenThread log level changes.
+ *
+ * This platform function is called whenever the OpenThread log level changes.
+ * This platform function is optional since an empty weak implementation has been provided.
+ *
+ * @note Only applicable when `OPENTHREAD_CONFIG_LOG_LEVEL_DYNAMIC_ENABLE=1`.
+ *
+ * @param[in]  aLogLevel  The new OpenThread log level.
+ *
+ */
+void otPlatLogHandleLevelChanged(otLogLevel aLogLevel);
+
 /**
  * @}
  *

src/core/common/instance.cpp

@@ -294,4 +294,22 @@ void Instance::GetBufferInfo(BufferInfo &aInfo)
 
 #endif // OPENTHREAD_MTD || OPENTHREAD_FTD
 
+#if OPENTHREAD_CONFIG_LOG_LEVEL_DYNAMIC_ENABLE
+
+void Instance::SetLogLevel(LogLevel aLogLevel)
+{
+    if (aLogLevel != sLogLevel)
+    {
+        sLogLevel = aLogLevel;
+        otPlatLogHandleLevelChanged(sLogLevel);
+    }
+}
+
+extern "C" OT_TOOL_WEAK void otPlatLogHandleLevelChanged(otLogLevel aLogLevel)
+{
+    OT_UNUSED_VARIABLE(aLogLevel);
+}
+
+#endif
+
 } // namespace ot

src/core/common/instance.hpp

@@ -207,7 +207,7 @@ public:
      * @param[in] aLogLevel  A log level.
      *
      */
-    static void SetLogLevel(LogLevel aLogLevel) { sLogLevel = aLogLevel; }
+    static void SetLogLevel(LogLevel aLogLevel);
 #endif
 
     /**