[discovery] allow (S)SED devices to perform MLE Discovery (#8832)

Signed-off-by: Lukasz Duda <[email protected]>

include/openthread/instance.h

@@ -53,7 +53,7 @@ extern "C" {
  * @note This number versions both OpenThread platform and user APIs.
  *
  */
-#define OPENTHREAD_API_VERSION (304)
+#define OPENTHREAD_API_VERSION (305)
 
 /**
  * @addtogroup api-instance

include/openthread/thread.h

@@ -264,6 +264,8 @@ bool otThreadIsSingleton(otInstance *aInstance);
 /**
  * This function starts a Thread Discovery scan.
  *
+ * @note A successful call to this function enables the rx-on-when-idle mode for the entire scan procedure.
+ *
  * @param[in]  aInstance              A pointer to an OpenThread instance.
  * @param[in]  aScanChannels          A bit vector indicating which channels to scan (e.g. OT_CHANNEL_11_MASK).
  * @param[in]  aPanId                 The PAN ID filter (set to Broadcast PAN to disable filter).

src/core/thread/discover_scanner.cpp

@@ -152,6 +152,12 @@ Error DiscoverScanner::Discover(const Mac::ChannelMask &aScanChannels,
     mScanChannel = Mac::ChannelMask::kChannelIteratorFirst;
     mState       = (mScanChannels.GetNextChannel(mScanChannel) == kErrorNone) ? kStateScanning : kStateScanDone;
 
+    // For rx-off-when-idle device, temporarily enable receiver during discovery procedure.
+    if (!Get<Mle>().IsDisabled() && !Get<Mle>().IsRxOnWhenIdle())
+    {
+        Get<MeshForwarder>().SetRxOnWhenIdle(true);
+    }
+
     Mle::Log(Mle::kMessageSend, Mle::kTypeDiscoveryRequest, destination);
 
 exit:
@@ -225,6 +231,12 @@ void DiscoverScanner::HandleDiscoveryRequestFrameTxDone(Message &aMessage)
 
 void DiscoverScanner::HandleDiscoverComplete(void)
 {
+    // Restore Data Polling or CSL for rx-off-when-idle device.
+    if (!Get<Mle>().IsDisabled() && !Get<Mle>().IsRxOnWhenIdle())
+    {
+        Get<MeshForwarder>().SetRxOnWhenIdle(false);
+    }
+
     switch (mState)
     {
     case kStateIdle:

src/core/thread/mesh_forwarder.cpp

@@ -733,7 +733,7 @@ Mac::TxFrame *MeshForwarder::HandleFrameRequest(Mac::TxFrames &aTxFrames)
             VerifyOrExit(frame != nullptr);
         }
 #if OPENTHREAD_CONFIG_MAC_CSL_RECEIVER_ENABLE
-        if (Get<Mac::Mac>().IsCslEnabled() && mSendMessage->IsSubTypeMle())
+        else if (Get<Mac::Mac>().IsCslEnabled() && mSendMessage->IsSubTypeMle())
         {
             mSendMessage->SetLinkSecurityEnabled(true);
         }
@@ -1669,7 +1669,10 @@ bool MeshForwarder::CalcIePresent(const Message *aMessage)
     iePresent |= (aMessage != nullptr && aMessage->IsTimeSync());
 #endif
 #if OPENTHREAD_CONFIG_MAC_CSL_RECEIVER_ENABLE
-    iePresent |= Get<Mac::Mac>().IsCslEnabled();
+    if (!(aMessage != nullptr && aMessage->GetSubType() == Message::kSubTypeMleDiscoverRequest))
+    {
+        iePresent |= Get<Mac::Mac>().IsCslEnabled();
+    }
 #endif
 #endif
 

src/core/thread/mle_router.cpp

@@ -2764,6 +2764,7 @@ Error MleRouter::SendDiscoveryResponse(const Ip6::Address &aDestination, const M
     uint16_t                      delay;
 
     VerifyOrExit((message = NewMleMessage(kCommandDiscoveryResponse)) != nullptr, error = kErrorNoBufs);
+    message->SetDirectTransmission();
     message->SetPanId(aDiscoverRequestMessage.GetPanId());
 #if OPENTHREAD_CONFIG_MULTI_RADIO
     // Send the MLE Discovery Response message on same radio link