From 6dda5c8408660bff2ad2ad9efd6be17ddcb87dd5 Mon Sep 17 00:00:00 2001
From: Jonathan Hui <jonhui@nestlabs.com>
Date: Wed, 4 Oct 2017 08:43:20 -0700
Subject: [PATCH] [mle] add link margin to parent selection criteria (#2242)

---
 src/core/thread/mle.cpp | 9 +++++++--
 src/core/thread/mle.hpp | 4 +++-
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/core/thread/mle.cpp b/src/core/thread/mle.cpp
index 507f82fdd..061295a05 100644
--- a/src/core/thread/mle.cpp
+++ b/src/core/thread/mle.cpp
@@ -79,6 +79,7 @@ Mle::Mle(ThreadNetif &aThreadNetif) :
     mParentLinkQuality2(0),
     mParentLinkQuality1(0),
     mChildUpdateAttempts(0),
+    mParentLinkMargin(0),
     mParentIsSingleton(false),
     mSocket(aThreadNetif.GetIp6().mUdp),
     mTimeout(kMleEndDeviceTimeout),
@@ -2523,7 +2524,8 @@ exit:
     return error;
 }
 
-bool Mle::IsBetterParent(uint16_t aRloc16, uint8_t aLinkQuality, ConnectivityTlv &aConnectivityTlv)
+bool Mle::IsBetterParent(uint16_t aRloc16, uint8_t aLinkQuality, uint8_t aLinkMargin,
+                         ConnectivityTlv &aConnectivityTlv)
 {
     bool rval = false;
 
@@ -2561,6 +2563,8 @@ bool Mle::IsBetterParent(uint16_t aRloc16, uint8_t aLinkQuality, ConnectivityTlv
         ExitNow(rval = (aConnectivityTlv.GetLinkQuality1() > mParentLinkQuality1));
     }
 
+    rval = (aLinkMargin > mParentLinkMargin);
+
 exit:
     return rval;
 }
@@ -2664,7 +2668,7 @@ otError Mle::HandleParentResponse(const Message &aMessage, const Ip6::MessageInf
         VerifyOrExit(compare >= 0);
 
         // only consider better parents if the partitions are the same
-        VerifyOrExit(compare != 0 || IsBetterParent(sourceAddress.GetRloc16(), linkQuality, connectivity));
+        VerifyOrExit(compare != 0 || IsBetterParent(sourceAddress.GetRloc16(), linkQuality, linkMargin, connectivity));
     }
 
     // Link Frame Counter
@@ -2707,6 +2711,7 @@ otError Mle::HandleParentResponse(const Message &aMessage, const Ip6::MessageInf
     mParentLeaderCost = connectivity.GetLeaderCost();
     mParentLeaderData = leaderData;
     mParentIsSingleton = connectivity.GetActiveRouters() <= 1;
+    mParentLinkMargin = linkMargin;
 
 exit:
 
diff --git a/src/core/thread/mle.hpp b/src/core/thread/mle.hpp
index c5a9a7dd4..3983a7090 100644
--- a/src/core/thread/mle.hpp
+++ b/src/core/thread/mle.hpp
@@ -1386,7 +1386,8 @@ private:
     otError SendChildIdRequest(void);
     void SendOrphanAnnounce(void);
 
-    bool IsBetterParent(uint16_t aRloc16, uint8_t aLinkQuality, ConnectivityTlv &aConnectivityTlv);
+    bool IsBetterParent(uint16_t aRloc16, uint8_t aLinkQuality, uint8_t aLinkMargin,
+                        ConnectivityTlv &aConnectivityTlv);
     void ResetParentCandidate(void);
 
 #if OPENTHREAD_CONFIG_INFORM_PREVIOUS_PARENT_ON_REATTACH
@@ -1415,6 +1416,7 @@ private:
     uint8_t mParentLinkQuality1;
     uint8_t mChildUpdateAttempts;
     LeaderDataTlv mParentLeaderData;
+    uint8_t mParentLinkMargin;
     bool mParentIsSingleton;
 
     Router mParentCandidate;