Invoke a padding round in certain use-cases.

* In some use-cases, it is possible that there are
no AppBuffer layers on the external/virtual layer-list
during which all the pipes will be allocated to the
primary. When layers do comeup on external/virtual
layer-list, subsequent overlay sets fail.

* This change ensures that in such cases, we invoke a
padding round on all the displays to free up the
hw resources which can be used in subsequent cycles.

Change-Id: Ifac0b8f51a8719eb55b11010d05b8d11352db054

libhwcomposer/hwc.cpp

@@ -105,7 +105,10 @@ static void hwc_registerProcs(struct hwc_composer_device_1* dev,
 //Helper
 static void reset(hwc_context_t *ctx, int numDisplays,
                   hwc_display_contents_1_t** displays) {
+
     ctx->numActiveDisplays = 0;
+    ctx->isPaddingRound = false;
+
     for(int i = 0; i < numDisplays; i++) {
         hwc_display_contents_1_t *list = displays[i];
         // XXX:SurfaceFlinger no longer guarantees that this
@@ -125,6 +128,17 @@ static void reset(hwc_context_t *ctx, int numDisplays,
              * the display device to be active.
              */
             ctx->numActiveDisplays += 1;
+
+            if((ctx->mPrevHwLayerCount[i] == 1) and (list->numHwLayers > 1)) {
+                /* If the previous cycle for dpy 'i' has 0 AppLayers and the
+                 * current cycle has atleast 1 AppLayer, padding round needs
+                 * to be invoked on current cycle to free up the resources.
+                 */
+                ctx->isPaddingRound = true;
+            }
+            ctx->mPrevHwLayerCount[i] = list->numHwLayers;
+        } else {
+            ctx->mPrevHwLayerCount[i] = 0;
         }
 
         if(ctx->mFBUpdate[i])
@@ -133,7 +147,6 @@ static void reset(hwc_context_t *ctx, int numDisplays,
             ctx->mCopyBit[i]->reset();
         if(ctx->mLayerRotMap[i])
             ctx->mLayerRotMap[i]->reset();
-
     }
 
     ctx->mAD->reset();

libhwcomposer/hwc_mdpcomp.cpp

@@ -419,8 +419,8 @@ bool MDPComp::isFrameDoable(hwc_context_t *ctx) {
                   __FUNCTION__);
         ret = false;
     } else if(ctx->isPaddingRound) {
-        ctx->isPaddingRound = false;
+        ALOGD_IF(isDebug(), "%s: padding round invoked for dpy %d",
-        ALOGD_IF(isDebug(), "%s: padding round",__FUNCTION__);
+                 __FUNCTION__,mDpy);
         ret = false;
     }
     return ret;
@@ -1410,11 +1410,10 @@ int MDPComp::prepare(hwc_context_t *ctx, hwc_display_contents_1_t* list) {
     const int numLayers = ctx->listStats[mDpy].numAppLayers;
     MDPVersion& mdpVersion = qdutils::MDPVersion::getInstance();
 
-    //number of app layers exceeds MAX_NUM_APP_LAYERS fall back to GPU
+    //Do not cache the information for next draw cycle.
-    //do not cache the information for next draw cycle.
+    if(numLayers > MAX_NUM_APP_LAYERS or (!numLayers)) {
-    if(numLayers > MAX_NUM_APP_LAYERS) {
+        ALOGI("%s: Unsupported layer count for mdp composition",
-        ALOGI("%s: Number of App layers exceeded the limit ",
+                __FUNCTION__);
-        __FUNCTION__);
         mCachedFrame.reset();
         return -1;
     }

libhwcomposer/hwc_utils.cpp

@@ -213,6 +213,10 @@ void initContext(hwc_context_t *ctx)
         ctx->dpyAttr[i].mAsHeightRatio = 0;
     }
 
+    for (uint32_t i = 0; i < HWC_NUM_DISPLAY_TYPES; i++) {
+        ctx->mPrevHwLayerCount[i] = 0;
+    }
+
     MDPComp::init(ctx);
     ctx->mAD = new AssertiveDisplay(ctx);
 
@@ -897,6 +901,7 @@ void setListStats(hwc_context_t *ctx,
     if(prevYuvCount != ctx->listStats[dpy].yuvCount) {
         ctx->mVideoTransFlag = true;
     }
+
     if(dpy == HWC_DISPLAY_PRIMARY) {
         ctx->mAD->markDoable(ctx, list);
     }

libhwcomposer/hwc_utils.h

@@ -483,6 +483,10 @@ struct hwc_context_t {
     eAnimationState mAnimationState[HWC_NUM_DISPLAY_TYPES];
     qhwc::HWCVirtualBase *mHWCVirtual;
 
+    // stores the #numHwLayers of the previous frame
+    // for each display device
+    int mPrevHwLayerCount[HWC_NUM_DISPLAY_TYPES];
+
     // stores the primary device orientation
     int deviceOrientation;
     //Securing in progress indicator