[mle] include Link Margin TLV in Child Update messages (openthread#10626

)

This commit adds code to include the Link Margin TLV in MLE Child
Update Request or Response messages sent by a parent to a child. This
allows the child to learn and update its "link quality out" to its
parent.

The change is designed to be backward compatible. Child devices
running older firmware will simply disregard this additional TLV.
When processing the message, the presence of the Link Margin TLV is
checked (it is optional).

src/core/thread/mle.cpp

@@ -3394,6 +3394,7 @@ void Mle::HandleChildUpdateRequest(RxInfo &aRxInfo)
     RxChallenge challenge;
     TlvList     requestedTlvList;
     TlvList     tlvList;
+    uint8_t     linkMarginOut;
 
     SuccessOrExit(error = Tlv::Find<SourceAddressTlv>(aRxInfo.mMessage, sourceAddress));
 
@@ -3436,6 +3437,17 @@ void Mle::HandleChildUpdateRequest(RxInfo &aRxInfo)
 
         SuccessOrExit(error = HandleLeaderData(aRxInfo));
 
+        switch (Tlv::Find<LinkMarginTlv>(aRxInfo.mMessage, linkMarginOut))
+        {
+        case kErrorNone:
+            mParent.SetLinkQualityOut(LinkQualityForLinkMargin(linkMarginOut));
+            break;
+        case kErrorNotFound:
+            break;
+        default:
+            ExitNow(error = kErrorParse);
+        }
+
 #if OPENTHREAD_CONFIG_MAC_CSL_RECEIVER_ENABLE
         {
             Mac::CslAccuracy cslAccuracy;
@@ -3494,6 +3506,7 @@ void Mle::HandleChildUpdateResponse(RxInfo &aRxInfo)
     uint32_t    mleFrameCounter;
     uint16_t    sourceAddress;
     uint32_t    timeout;
+    uint8_t     linkMarginOut;
 
     Log(kMessageReceive, kTypeChildUpdateResponseAsChild, aRxInfo.mMessageInfo.GetPeerAddr());
 
@@ -3616,6 +3629,17 @@ void Mle::HandleChildUpdateResponse(RxInfo &aRxInfo)
         OT_ASSERT(false);
     }
 
+    switch (Tlv::Find<LinkMarginTlv>(aRxInfo.mMessage, linkMarginOut))
+    {
+    case kErrorNone:
+        mParent.SetLinkQualityOut(LinkQualityForLinkMargin(linkMarginOut));
+        break;
+    case kErrorNotFound:
+        break;
+    default:
+        ExitNow(error = kErrorParse);
+    }
+
     aRxInfo.mClass = response.IsEmpty() ? RxInfo::kPeerMessage : RxInfo::kAuthoritativeMessage;
 
 exit:

src/core/thread/mle_router.cpp

@@ -2211,6 +2211,7 @@ void MleRouter::HandleChildUpdateRequest(RxInfo &aRxInfo)
     child->SetDeviceMode(mode);
 
     tlvList.Add(Tlv::kMode);
+    tlvList.Add(Tlv::kLinkMargin);
 
     // Parent MUST include Leader Data TLV in Child Update Response
     tlvList.Add(Tlv::kLeaderData);
@@ -2921,7 +2922,11 @@ Error MleRouter::SendChildUpdateRequest(Child &aChild)
     SuccessOrExit(error = message->AppendNetworkDataTlv(aChild.GetNetworkDataType()));
     SuccessOrExit(error = message->AppendActiveAndPendingTimestampTlvs());
 
-    if (!aChild.IsStateValid())
+    if (aChild.IsStateValid())
+    {
+        SuccessOrExit(error = message->AppendLinkMarginTlv(aChild.GetLinkInfo().GetLinkMargin()));
+    }
+    else
     {
         SuccessOrExit(error = message->AppendTlvRequestTlv(kTlvs));
 
@@ -3029,6 +3034,10 @@ void MleRouter::SendChildUpdateResponse(Child                  *aChild,
             SuccessOrExit(error = message->AppendTimeoutTlv(aChild->GetTimeout()));
             break;
 
+        case Tlv::kLinkMargin:
+            SuccessOrExit(error = message->AppendLinkMarginTlv(aChild->GetLinkInfo().GetLinkMargin()));
+            break;
+
         case Tlv::kSupervisionInterval:
             SuccessOrExit(error = message->AppendSupervisionIntervalTlv(aChild->GetSupervisionInterval()));
             break;