diff --git a/drm/common/DrmInfoEvent.cpp b/drm/common/DrmInfoEvent.cpp
index 27a5a2d..703e363 100644
--- a/drm/common/DrmInfoEvent.cpp
+++ b/drm/common/DrmInfoEvent.cpp
@@ -19,7 +19,7 @@
 
 using namespace android;
 
-DrmInfoEvent::DrmInfoEvent(int uniqueId, int infoType, const String8 message)
+DrmInfoEvent::DrmInfoEvent(int uniqueId, int infoType, const String8 &message)
     : mUniqueId(uniqueId),
       mInfoType(infoType),
       mMessage(message) {
diff --git a/drm/drmserver/DrmManager.cpp b/drm/drmserver/DrmManager.cpp
index c27561b..1d835f9 100644
--- a/drm/drmserver/DrmManager.cpp
+++ b/drm/drmserver/DrmManager.cpp
@@ -413,7 +413,7 @@
         handle->decryptId = mDecryptSessionId + 1;
 
         for (size_t index = 0; index < plugInIdList.size(); index++) {
-            String8 plugInId = plugInIdList.itemAt(index);
+            const String8& plugInId = plugInIdList.itemAt(index);
             IDrmEngine& rDrmEngine = mPlugInManager.getPlugIn(plugInId);
             result = rDrmEngine.openDecryptSession(uniqueId, handle, fd, offset, length, mime);
 
@@ -441,7 +441,7 @@
         handle->decryptId = mDecryptSessionId + 1;
 
         for (size_t index = 0; index < plugInIdList.size(); index++) {
-            String8 plugInId = plugInIdList.itemAt(index);
+            const String8& plugInId = plugInIdList.itemAt(index);
             IDrmEngine& rDrmEngine = mPlugInManager.getPlugIn(plugInId);
             result = rDrmEngine.openDecryptSession(uniqueId, handle, uri, mime);
 
@@ -470,7 +470,7 @@
         handle->decryptId = mDecryptSessionId + 1;
 
         for (size_t index = 0; index < plugInIdList.size(); index++) {
-            String8 plugInId = plugInIdList.itemAt(index);
+            const String8& plugInId = plugInIdList.itemAt(index);
             IDrmEngine& rDrmEngine = mPlugInManager.getPlugIn(plugInId);
             result = rDrmEngine.openDecryptSession(uniqueId, handle, buf, mimeType);
 
diff --git a/drm/libdrmframework/include/IDrmManagerService.h b/drm/libdrmframework/include/IDrmManagerService.h
index fe55650..0376b49 100644
--- a/drm/libdrmframework/include/IDrmManagerService.h
+++ b/drm/libdrmframework/include/IDrmManagerService.h
@@ -169,7 +169,7 @@
 class BpDrmManagerService: public BpInterface<IDrmManagerService>
 {
 public:
-    BpDrmManagerService(const sp<IBinder>& impl)
+    explicit BpDrmManagerService(const sp<IBinder>& impl)
             : BpInterface<IDrmManagerService>(impl) {}
 
     virtual int addUniqueId(bool isNative);
diff --git a/drm/libdrmframework/include/IDrmServiceListener.h b/drm/libdrmframework/include/IDrmServiceListener.h
index 7f7109f..78c5d1a 100644
--- a/drm/libdrmframework/include/IDrmServiceListener.h
+++ b/drm/libdrmframework/include/IDrmServiceListener.h
@@ -49,7 +49,7 @@
 class BpDrmServiceListener: public BpInterface<IDrmServiceListener>
 {
 public:
-    BpDrmServiceListener(const sp<IBinder>& impl)
+    explicit BpDrmServiceListener(const sp<IBinder>& impl)
             : BpInterface<IDrmServiceListener>(impl) {}
 
     virtual status_t notify(const DrmInfoEvent& event);
diff --git a/drm/libdrmframework/plugins/forward-lock/FwdLockEngine/include/FwdLockEngine.h b/drm/libdrmframework/plugins/forward-lock/FwdLockEngine/include/FwdLockEngine.h
index a31b951..d222703 100644
--- a/drm/libdrmframework/plugins/forward-lock/FwdLockEngine/include/FwdLockEngine.h
+++ b/drm/libdrmframework/plugins/forward-lock/FwdLockEngine/include/FwdLockEngine.h
@@ -539,7 +539,7 @@
             offset = 0;
         }
 
-        DecodeSession(int fd) {
+        explicit DecodeSession(int fd) {
             fileDesc = fd;
             offset = 0;
         }
diff --git a/drm/libmediadrm/DrmSessionManager.cpp b/drm/libmediadrm/DrmSessionManager.cpp
index a87fb9d..02270d0 100644
--- a/drm/libmediadrm/DrmSessionManager.cpp
+++ b/drm/libmediadrm/DrmSessionManager.cpp
@@ -65,7 +65,7 @@
 DrmSessionManager::~DrmSessionManager() {}
 
 void DrmSessionManager::addSession(
-        int pid, sp<DrmSessionClientInterface> drm, const Vector<uint8_t> &sessionId) {
+        int pid, const sp<DrmSessionClientInterface>& drm, const Vector<uint8_t> &sessionId) {
     ALOGV("addSession(pid %d, drm %p, sessionId %s)", pid, drm.get(),
             GetSessionIdString(sessionId).string());
 
@@ -116,7 +116,7 @@
     }
 }
 
-void DrmSessionManager::removeDrm(sp<DrmSessionClientInterface> drm) {
+void DrmSessionManager::removeDrm(const sp<DrmSessionClientInterface>& drm) {
     ALOGV("removeDrm(%p)", drm.get());
 
     Mutex::Autolock lock(mLock);
diff --git a/drm/mediadrm/plugins/clearkey/CryptoPlugin.h b/drm/mediadrm/plugins/clearkey/CryptoPlugin.h
index de84c36..a6d2f7b 100644
--- a/drm/mediadrm/plugins/clearkey/CryptoPlugin.h
+++ b/drm/mediadrm/plugins/clearkey/CryptoPlugin.h
@@ -31,7 +31,7 @@
 
 class CryptoPlugin : public android::CryptoPlugin {
 public:
-    CryptoPlugin(const android::Vector<uint8_t>& sessionId) {
+    explicit CryptoPlugin(const android::Vector<uint8_t>& sessionId) {
         mInitStatus = setMediaDrmSession(sessionId);
     }
 
diff --git a/drm/mediadrm/plugins/clearkey/DrmPlugin.h b/drm/mediadrm/plugins/clearkey/DrmPlugin.h
index 9095045..820bda2 100644
--- a/drm/mediadrm/plugins/clearkey/DrmPlugin.h
+++ b/drm/mediadrm/plugins/clearkey/DrmPlugin.h
@@ -39,7 +39,7 @@
 
 class DrmPlugin : public android::DrmPlugin {
 public:
-    DrmPlugin(SessionLibrary* sessionLibrary)
+    explicit DrmPlugin(SessionLibrary* sessionLibrary)
             : mSessionLibrary(sessionLibrary) {}
     virtual ~DrmPlugin() {}
 
diff --git a/drm/mediadrm/plugins/mock/MockDrmCryptoPlugin.cpp b/drm/mediadrm/plugins/mock/MockDrmCryptoPlugin.cpp
index 1e80f8e..a38cca9 100644
--- a/drm/mediadrm/plugins/mock/MockDrmCryptoPlugin.cpp
+++ b/drm/mediadrm/plugins/mock/MockDrmCryptoPlugin.cpp
@@ -766,7 +766,7 @@
         return result;
     }
 
-    String8 MockDrmPlugin::stringMapToString(KeyedVector<String8, String8> map) const
+    String8 MockDrmPlugin::stringMapToString(const KeyedVector<String8, String8>& map) const
     {
         String8 result("{ ");
         for (size_t i = 0; i < map.size(); i++) {
diff --git a/drm/mediadrm/plugins/mock/MockDrmCryptoPlugin.h b/drm/mediadrm/plugins/mock/MockDrmCryptoPlugin.h
index 40d4e84..98bdd69 100644
--- a/drm/mediadrm/plugins/mock/MockDrmCryptoPlugin.h
+++ b/drm/mediadrm/plugins/mock/MockDrmCryptoPlugin.h
@@ -138,7 +138,7 @@
     private:
         String8 vectorToString(Vector<uint8_t> const &vector) const;
         String8 arrayToString(uint8_t const *array, size_t len) const;
-        String8 stringMapToString(KeyedVector<String8, String8> map) const;
+        String8 stringMapToString(const KeyedVector<String8, String8>& map) const;
 
         SortedVector<Vector<uint8_t> > mSessions;
         SortedVector<Vector<uint8_t> > mKeySets;
diff --git a/include/drm/DrmConstraints.h b/include/drm/DrmConstraints.h
index a9ec942..b8bb24f 100644
--- a/include/drm/DrmConstraints.h
+++ b/include/drm/DrmConstraints.h
@@ -70,7 +70,7 @@
     class KeyIterator {
         friend class DrmConstraints;
     private:
-        KeyIterator(DrmConstraints* drmConstraints)
+        explicit KeyIterator(DrmConstraints* drmConstraints)
             : mDrmConstraints(drmConstraints), mIndex(0) {}
 
     public:
@@ -93,7 +93,7 @@
     class Iterator {
         friend class DrmConstraints;
     private:
-        Iterator(DrmConstraints* drmConstraints)
+        explicit Iterator(DrmConstraints* drmConstraints)
             : mDrmConstraints(drmConstraints), mIndex(0) {}
 
     public:
diff --git a/include/drm/DrmInfo.h b/include/drm/DrmInfo.h
index 7b48541..53dfd61 100644
--- a/include/drm/DrmInfo.h
+++ b/include/drm/DrmInfo.h
@@ -55,7 +55,7 @@
         friend class DrmInfo;
 
     private:
-        KeyIterator(const DrmInfo* drmInfo)
+        explicit KeyIterator(const DrmInfo* drmInfo)
             : mDrmInfo(const_cast <DrmInfo*> (drmInfo)), mIndex(0) {}
 
     public:
@@ -79,7 +79,7 @@
         friend class DrmInfo;
 
     private:
-        Iterator(const DrmInfo* drmInfo)
+        explicit Iterator(const DrmInfo* drmInfo)
             : mDrmInfo(const_cast <DrmInfo*> (drmInfo)), mIndex(0) {}
 
     public:
diff --git a/include/drm/DrmInfoEvent.h b/include/drm/DrmInfoEvent.h
index dfca228..3165f02 100644
--- a/include/drm/DrmInfoEvent.h
+++ b/include/drm/DrmInfoEvent.h
@@ -77,7 +77,7 @@
      * @param[in] infoType Type of information
      * @param[in] message Message description
      */
-    DrmInfoEvent(int uniqueId, int infoType, const String8 message);
+    DrmInfoEvent(int uniqueId, int infoType, const String8& message);
 
     /**
      * Destructor for DrmInfoEvent
diff --git a/include/drm/DrmInfoRequest.h b/include/drm/DrmInfoRequest.h
index 3e48ecc..e2da4fe 100644
--- a/include/drm/DrmInfoRequest.h
+++ b/include/drm/DrmInfoRequest.h
@@ -69,7 +69,7 @@
         friend class DrmInfoRequest;
 
     private:
-        KeyIterator(const DrmInfoRequest* drmInfoRequest)
+        explicit KeyIterator(const DrmInfoRequest* drmInfoRequest)
             : mDrmInfoRequest(const_cast <DrmInfoRequest*> (drmInfoRequest)), mIndex(0) {}
 
     public:
@@ -93,7 +93,7 @@
         friend class DrmInfoRequest;
 
     private:
-        Iterator(const DrmInfoRequest* drmInfoRequest)
+        explicit Iterator(const DrmInfoRequest* drmInfoRequest)
             : mDrmInfoRequest(const_cast <DrmInfoRequest*> (drmInfoRequest)), mIndex(0) {}
 
     public:
diff --git a/include/drm/DrmMetadata.h b/include/drm/DrmMetadata.h
index 2c7538a..6624450 100644
--- a/include/drm/DrmMetadata.h
+++ b/include/drm/DrmMetadata.h
@@ -35,7 +35,7 @@
     class KeyIterator {
         friend class DrmMetadata;
     private:
-        KeyIterator(DrmMetadata* drmMetadata) : mDrmMetadata(drmMetadata), mIndex(0) {}
+        explicit KeyIterator(DrmMetadata* drmMetadata) : mDrmMetadata(drmMetadata), mIndex(0) {}
 
     public:
         KeyIterator(const KeyIterator& keyIterator);
@@ -57,7 +57,7 @@
     class Iterator {
         friend class DrmMetadata;
     private:
-        Iterator(DrmMetadata* drmMetadata) : mDrmMetadata(drmMetadata), mIndex(0) {}
+        explicit Iterator(DrmMetadata* drmMetadata) : mDrmMetadata(drmMetadata), mIndex(0) {}
 
     public:
         Iterator(const Iterator& iterator);
diff --git a/include/drm/DrmSupportInfo.h b/include/drm/DrmSupportInfo.h
index bf12b0b..bf85dbb 100644
--- a/include/drm/DrmSupportInfo.h
+++ b/include/drm/DrmSupportInfo.h
@@ -37,7 +37,7 @@
     class MimeTypeIterator {
         friend class DrmSupportInfo;
     private:
-        MimeTypeIterator(DrmSupportInfo* drmSupportInfo)
+        explicit MimeTypeIterator(DrmSupportInfo* drmSupportInfo)
            : mDrmSupportInfo(drmSupportInfo), mIndex(0) {}
     public:
         MimeTypeIterator(const MimeTypeIterator& iterator);
@@ -60,7 +60,7 @@
        friend class DrmSupportInfo;
 
     private:
-        FileSuffixIterator(DrmSupportInfo* drmSupportInfo)
+        explicit FileSuffixIterator(DrmSupportInfo* drmSupportInfo)
             : mDrmSupportInfo(drmSupportInfo), mIndex(0) {}
     public:
         FileSuffixIterator(const FileSuffixIterator& iterator);
diff --git a/include/media/DrmSessionManager.h b/include/media/DrmSessionManager.h
index ba5c268..ba27199 100644
--- a/include/media/DrmSessionManager.h
+++ b/include/media/DrmSessionManager.h
@@ -45,12 +45,12 @@
     static sp<DrmSessionManager> Instance();
 
     DrmSessionManager();
-    DrmSessionManager(sp<ProcessInfoInterface> processInfo);
+    explicit DrmSessionManager(sp<ProcessInfoInterface> processInfo);
 
-    void addSession(int pid, sp<DrmSessionClientInterface> drm, const Vector<uint8_t>& sessionId);
+    void addSession(int pid, const sp<DrmSessionClientInterface>& drm, const Vector<uint8_t>& sessionId);
     void useSession(const Vector<uint8_t>& sessionId);
     void removeSession(const Vector<uint8_t>& sessionId);
-    void removeDrm(sp<DrmSessionClientInterface> drm);
+    void removeDrm(const sp<DrmSessionClientInterface>& drm);
     bool reclaimSession(int callingPid);
 
 protected:
diff --git a/services/radio/RadioService.h b/services/radio/RadioService.h
index 49feda6..ac3481e 100644
--- a/services/radio/RadioService.h
+++ b/services/radio/RadioService.h
@@ -103,7 +103,7 @@
     class CallbackThread : public Thread {
     public:
 
-        CallbackThread(const wp<ModuleClient>& moduleClient);
+        explicit CallbackThread(const wp<ModuleClient>& moduleClient);
 
         virtual ~CallbackThread();
 
diff --git a/services/soundtrigger/SoundTriggerHwService.cpp b/services/soundtrigger/SoundTriggerHwService.cpp
index bb2416a..ac379bd 100644
--- a/services/soundtrigger/SoundTriggerHwService.cpp
+++ b/services/soundtrigger/SoundTriggerHwService.cpp
@@ -164,7 +164,7 @@
 }
 
 
-void SoundTriggerHwService::detachModule(sp<Module> module)
+void SoundTriggerHwService::detachModule(const sp<Module>& module)
 {
     ALOGV("detachModule");
     AutoMutex lock(mServiceLock);
diff --git a/services/soundtrigger/SoundTriggerHwService.h b/services/soundtrigger/SoundTriggerHwService.h
index 2619a5f..13a577a 100644
--- a/services/soundtrigger/SoundTriggerHwService.h
+++ b/services/soundtrigger/SoundTriggerHwService.h
@@ -125,7 +125,7 @@
 
        sound_trigger_hw_device *hwDevice() const { return mHwDevice; }
        struct sound_trigger_module_descriptor descriptor() { return mDescriptor; }
-       void setClient(sp<ISoundTriggerClient> client) { mClient = client; }
+       void setClient(const sp<ISoundTriggerClient>& client) { mClient = client; }
        void clearClient() { mClient.clear(); }
        sp<ISoundTriggerClient> client() const { return mClient; }
        wp<SoundTriggerHwService> service() const { return mService; }
@@ -156,7 +156,7 @@
     class CallbackThread : public Thread {
     public:
 
-        CallbackThread(const wp<SoundTriggerHwService>& service);
+        explicit CallbackThread(const wp<SoundTriggerHwService>& service);
 
         virtual             ~CallbackThread();
 
@@ -176,7 +176,7 @@
         Vector< sp<CallbackEvent> > mEventQueue;
     };
 
-           void detachModule(sp<Module> module);
+           void detachModule(const sp<Module>& module);
 
     static void recognitionCallback(struct sound_trigger_recognition_event *event, void *cookie);
            sp<IMemory> prepareRecognitionEvent_l(struct sound_trigger_recognition_event *event);