audioflinger: fix audio skipping over A2DP

The maximum sleep time allowed in the mixer thread when audio tracks
are enabled but not ready for mixing is derived from the latency
reported by the output stream.
This does not work for A2DP where the latency also reflects encoding, decoding
and transfer time.

Modified activeSleepTimeUs() to take A2DP case into account.

Issue 5682206.

Change-Id: I3784ac01fb6f836b5a6ce6f764fb15347586de35

Author: Eric Laurent

services/audioflinger/AudioFlinger.cpp

@@ -1816,6 +1816,18 @@ audio_stream_t* AudioFlinger::PlaybackThread::stream()
     return &mOutput->stream->common;
 }
 
+uint32_t AudioFlinger::PlaybackThread::activeSleepTimeUs()
+{
+    // A2DP output latency is not due only to buffering capacity. It also reflects encoding,
+    // decoding and transfer time. So sleeping for half of the latency would likely cause
+    // underruns
+    if (audio_is_a2dp_device((audio_devices_t)mDevice)) {
+        return (uint32_t)((uint32_t)((mFrameCount * 1000) / mSampleRate) * 1000);
+    } else {
+        return (uint32_t)(mOutput->stream->get_latency(mOutput->stream) * 1000) / 2;
+    }
+}
+
 // ----------------------------------------------------------------------------
 
 AudioFlinger::MixerThread::MixerThread(const sp<AudioFlinger>& audioFlinger, AudioStreamOut* output, int id, uint32_t device)
@@ -2422,11 +2434,6 @@ status_t AudioFlinger::MixerThread::dumpInternals(int fd, const Vector<String16>
     return NO_ERROR;
 }
 
-uint32_t AudioFlinger::MixerThread::activeSleepTimeUs()
-{
-    return (uint32_t)(mOutput->stream->get_latency(mOutput->stream) * 1000) / 2;
-}
-
 uint32_t AudioFlinger::MixerThread::idleSleepTimeUs()
 {
     return (uint32_t)(((mFrameCount * 1000) / mSampleRate) * 1000) / 2;
@@ -2893,7 +2900,7 @@ uint32_t AudioFlinger::DirectOutputThread::activeSleepTimeUs()
 {
     uint32_t time;
     if (audio_is_linear_pcm(mFormat)) {
-        time = (uint32_t)(mOutput->stream->get_latency(mOutput->stream) * 1000) / 2;
+        time = PlaybackThread::activeSleepTimeUs();
     } else {
         time = 10000;
     }

services/audioflinger/AudioFlinger.h

@@ -776,7 +776,7 @@ class AudioFlinger :
 
         virtual int             getTrackName_l() = 0;
         virtual void            deleteTrackName_l(int name) = 0;
-        virtual uint32_t        activeSleepTimeUs() = 0;
+        virtual uint32_t        activeSleepTimeUs();
         virtual uint32_t        idleSleepTimeUs() = 0;
         virtual uint32_t        suspendSleepTimeUs() = 0;
 
@@ -833,7 +833,6 @@ class AudioFlinger :
                                                 Vector< sp<Track> > *tracksToRemove);
         virtual     int         getTrackName_l();
         virtual     void        deleteTrackName_l(int name);
-        virtual     uint32_t    activeSleepTimeUs();
         virtual     uint32_t    idleSleepTimeUs();
         virtual     uint32_t    suspendSleepTimeUs();