DO NOT MERGE Bluetooth: Restrict gain for Absolute volume case

For the lowest music volume steps 1 and 2, restrict the gain to 50% and
75%. This will avoid the lowest volume steps being too loud for some
accessories. For music volume 0, set phone gain to 0 as some
accessories won't mute on their end.

Change-Id: I24e0fa7be8c8635b428a11c91ea153aad7cec55f
Signed-off-by: Liejun Tao <baibai@motorola.com>

Author: Liejun Tao

services/core/java/com/android/server/audio/AudioService.java

@@ -3737,8 +3737,29 @@ public void applyDeviceVolume_syncVSS(int device) {
             int index;
             if (mIsMuted) {
                 index = 0;
-            } else if (((device & AudioSystem.DEVICE_OUT_ALL_A2DP) != 0 && mAvrcpAbsVolSupported)
-                    || ((device & mFullVolumeDevices) != 0)) {
+            } else if ((device & AudioSystem.DEVICE_OUT_ALL_A2DP) != 0 && mAvrcpAbsVolSupported) {
+                /* Special handling for Bluetooth Absolute Volume scenario
+                 * If we send full audio gain, some accessories are too loud even at its lowest
+                 * volume. We are not able to enumerate all such accessories, so here is the
+                 * workaround from phone side.
+                 * For the lowest volume steps 1 and 2, restrict audio gain to 50% and 75%.
+                 * For volume step 0, set audio gain to 0 as some accessories won't mute on their end.
+                 */
+                int i = (getIndex(device) + 5)/10;
+                if (i == 0) {
+                    // 0% for volume 0
+                    index = 0;
+                } else if (i == 1) {
+                    // 50% for volume 1
+                    index = (int)(mIndexMax * 0.5) /10;
+                } else if (i == 2) {
+                    // 75% for volume 2
+                    index = (int)(mIndexMax * 0.75) /10;
+                } else {
+                    // otherwise, full gain
+                    index = (mIndexMax + 5)/10;
+                }
+            } else if ((device & mFullVolumeDevices) != 0) {
                 index = (mIndexMax + 5)/10;
             } else {
                 index = (getIndex(device) + 5)/10;