audio: Report unknown stream positions explicitly

Instead of using 'STATUS_NO_INIT' in the case when stream
position can not be reported, use a special value for Position
fields. This streamlines processing of statuses on the client
side, by removing the need to treat 'STATUS_NO_INIT' specially.

Bug: 205884982
Test: atest VtsHalAudioCoreTargetTest
Change-Id: I13c9c8d165b632900ca76de144759ef7b9200eff

audio/aidl/aidl_api/android.hardware.audio.core/current/android/hardware/audio/core/StreamDescriptor.aidl

@@ -42,8 +42,9 @@ parcelable StreamDescriptor {
   const int LATENCY_UNKNOWN = -1;
   @FixedSize @VintfStability
   parcelable Position {
-    long frames;
-    long timeNs;
+    long frames = -1;
+    long timeNs = -1;
+    const long UNKNOWN = -1;
   }
   @Backing(type="int") @VintfStability
   enum State {

audio/aidl/android/hardware/audio/core/StreamDescriptor.aidl

@@ -116,10 +116,15 @@ parcelable StreamDescriptor {
     @VintfStability
     @FixedSize
     parcelable Position {
+        /**
+         * The value used when the position can not be reported by the HAL
+         * module.
+         */
+        const long UNKNOWN = -1;
         /** Frame count. */
-        long frames;
+        long frames = UNKNOWN;
         /** Timestamp in nanoseconds. */
-        long timeNs;
+        long timeNs = UNKNOWN;
     }
 
     @VintfStability
@@ -295,10 +300,6 @@ parcelable StreamDescriptor {
          *  - STATUS_INVALID_OPERATION: the command is not applicable in the
          *                              current state of the stream, or to this
          *                              type of the stream;
-         *  - STATUS_NO_INIT: positions can not be reported because the mix port
-         *                    is not connected to any producer or consumer, or
-         *                    because the HAL module does not support positions
-         *                    reporting for this AudioSource (on input streams).
          *  - STATUS_NOT_ENOUGH_DATA: a read or write error has
          *                            occurred for the 'audio.fmq' queue;
          */
@@ -316,9 +317,11 @@ parcelable StreamDescriptor {
          */
         int fmqByteCount;
         /**
-         * It is recommended to report the current position for any command.
-         * If the position can not be reported, the 'status' field must be
-         * set to 'NO_INIT'.
+         * It is recommended to report the current position for any command. If
+         * the position can not be reported, for example because the mix port is
+         * not connected to any producer or consumer, or because the HAL module
+         * does not support positions reporting for this AudioSource (on input
+         * streams), the 'Position::UNKNOWN' value must be used.
          *
          * For output streams: the moment when the specified stream position
          *   was presented to an external observer (i.e. presentation position).

audio/aidl/default/Stream.cpp

@@ -87,12 +87,13 @@ std::string StreamWorkerCommonLogic::init() {
 
 void StreamWorkerCommonLogic::populateReply(StreamDescriptor::Reply* reply,
                                             bool isConnected) const {
+    reply->status = STATUS_OK;
     if (isConnected) {
-        reply->status = STATUS_OK;
         reply->observable.frames = mFrameCount;
         reply->observable.timeNs = ::android::elapsedRealtimeNano();
     } else {
-        reply->status = STATUS_NO_INIT;
+        reply->observable.frames = StreamDescriptor::Position::UNKNOWN;
+        reply->observable.timeNs = StreamDescriptor::Position::UNKNOWN;
     }
 }
 

audio/aidl/vts/VtsHalAudioCoreTargetTest.cpp

@@ -1660,14 +1660,16 @@ class StreamLogicDefaultDriver : public StreamLogicDriver {
     }
     bool interceptRawReply(const StreamDescriptor::Reply&) override { return false; }
     bool processValidReply(const StreamDescriptor::Reply& reply) override {
-        if (mPreviousFrames.has_value()) {
-            if (reply.observable.frames > mPreviousFrames.value()) {
-                mObservablePositionIncrease = true;
-            } else if (reply.observable.frames < mPreviousFrames.value()) {
-                mRetrogradeObservablePosition = true;
+        if (reply.observable.frames != StreamDescriptor::Position::UNKNOWN) {
+            if (mPreviousFrames.has_value()) {
+                if (reply.observable.frames > mPreviousFrames.value()) {
+                    mObservablePositionIncrease = true;
+                } else if (reply.observable.frames < mPreviousFrames.value()) {
+                    mRetrogradeObservablePosition = true;
+                }
             }
+            mPreviousFrames = reply.observable.frames;
         }
-        mPreviousFrames = reply.observable.frames;
 
         const auto& lastCommandState = mCommands[mNextCommand - 1];
         if (lastCommandState.second != reply.state) {