Limit cached timestamp use if HW fails to provide them

On some devices, if the HDMI cable is disconnected during use,
cached timestamp info can become very old.

Bug: 29423451
Change-Id: Ieecf5e98bad14d00b4f5f14b032c2cf66ae94ceb
diff --git a/media/libmedia/AudioTrack.cpp b/media/libmedia/AudioTrack.cpp
index 1963da3..e8da341 100644
--- a/media/libmedia/AudioTrack.cpp
+++ b/media/libmedia/AudioTrack.cpp
@@ -2374,9 +2374,14 @@
                 if (location == ExtendedTimestamp::LOCATION_SERVER) {
                     ALOGW_IF(mPreviousLocation == ExtendedTimestamp::LOCATION_KERNEL,
                             "getTimestamp() location moved from kernel to server");
+                    // check that the last kernel OK time info exists and the positions
+                    // are valid (if they predate the current track, the positions may
+                    // be zero or negative).
                     const int64_t frames =
                             (ets.mTimeNs[ExtendedTimestamp::LOCATION_SERVER_LASTKERNELOK] < 0 ||
-                            ets.mTimeNs[ExtendedTimestamp::LOCATION_KERNEL_LASTKERNELOK] < 0)
+                            ets.mTimeNs[ExtendedTimestamp::LOCATION_KERNEL_LASTKERNELOK] < 0 ||
+                            ets.mPosition[ExtendedTimestamp::LOCATION_SERVER_LASTKERNELOK] <= 0 ||
+                            ets.mPosition[ExtendedTimestamp::LOCATION_KERNEL_LASTKERNELOK] <= 0)
                             ?
                             int64_t((double)mAfLatency * mSampleRate * mPlaybackRate.mSpeed
                                     / 1000)
diff --git a/services/audioflinger/FastMixer.cpp b/services/audioflinger/FastMixer.cpp
index 546ef25..01f3939 100644
--- a/services/audioflinger/FastMixer.cpp
+++ b/services/audioflinger/FastMixer.cpp
@@ -482,8 +482,6 @@
             } else {
                 // HAL reported that more frames were presented than were written
                 mNativeFramesWrittenButNotPresented = 0;
-                mTimestamp.mPosition[ExtendedTimestamp::LOCATION_KERNEL] = 0;
-                mTimestamp.mTimeNs[ExtendedTimestamp::LOCATION_KERNEL] = -1;
                 status = INVALID_OPERATION;
             }
         }
@@ -494,6 +492,10 @@
             // fetch server time if we can't get timestamp
             mTimestamp.mTimeNs[ExtendedTimestamp::LOCATION_SERVER] =
                     systemTime(SYSTEM_TIME_MONOTONIC);
+            // clear out kernel cached position as this may get rapidly stale
+            // if we never get a new valid timestamp
+            mTimestamp.mPosition[ExtendedTimestamp::LOCATION_KERNEL] = 0;
+            mTimestamp.mTimeNs[ExtendedTimestamp::LOCATION_KERNEL] = -1;
         }
     }
 }