From 01bc63ac0e96a950823fa59479a2a52c275f909b Mon Sep 17 00:00:00 2001
From: Rongli Sun <rongli@google.com>
Date: Fri, 15 Jan 2021 02:18:56 +0800
Subject: [PATCH] [doc] amend DUA and MLR fast poll comments (#6065)

---
 src/core/thread/dua_manager.cpp | 4 +++-
 src/core/thread/mlr_manager.cpp | 6 ++++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/core/thread/dua_manager.cpp b/src/core/thread/dua_manager.cpp
index 5ab918b4a..ab3ad4706 100644
--- a/src/core/thread/dua_manager.cpp
+++ b/src/core/thread/dua_manager.cpp
@@ -509,7 +509,9 @@ void DuaManager::PerformNextRegistration(void)
     mIsDuaPending   = true;
     mRegisteringDua = dua;
 
-    // TODO: (DUA) need update when CSL is enabled.
+    // Generally Thread 1.2 Router would send DUA.req on behalf for DUA registered by its MTD child.
+    // When Thread 1.2 MTD attaches to Thread 1.1 parent, 1.2 MTD should send DUA.req to PBBR itself.
+    // In this case, Thread 1.2 sleepy end device relies on fast data poll to fetch the response timely.
     if (!Get<Mle::Mle>().IsRxOnWhenIdle())
     {
         Get<DataPollSender>().SendFastPolls();
diff --git a/src/core/thread/mlr_manager.cpp b/src/core/thread/mlr_manager.cpp
index 287ec602b..88c2bc958 100644
--- a/src/core/thread/mlr_manager.cpp
+++ b/src/core/thread/mlr_manager.cpp
@@ -290,10 +290,12 @@ void MlrManager::SendMulticastListenerRegistration(void)
 
     mMlrPending = true;
 
-    // TODO: not enable fast polls for SSED
+    // Generally Thread 1.2 Router would send MLR.req on bebelf for MA (scope >=4) subscribed by its MTD child.
+    // When Thread 1.2 MTD attaches to Thread 1.1 parent, 1.2 MTD should send MLR.req to PBBR itself.
+    // In this case, Thread 1.2 sleepy end device relies on fast data poll to fetch the response timely.
     if (!Get<Mle::Mle>().IsRxOnWhenIdle())
     {
-        Get<DataPollSender>().SendFastPolls(DataPollSender::kDefaultFastPolls);
+        Get<DataPollSender>().SendFastPolls();
     }
 
 exit: