commit 8fae156cf9127c61fc3ba998e71de85b737ac3e8
author Roman Kovalivskyi <roman.kovalivskyi@globallogic.com> Thu Jan 30 20:20:47 2020 +0200
committer Roman Kovalivskyi <roman.kovalivskyi@globallogic.com> Wed Feb 19 17:08:20 2020 +0200
tree 3b4b8d5f0ac8e2f62f6ffa7b95c99610a0fb5d08
parent 65f2ba80df03635a75c7ecd70f8a39c0d76bd425

drm_hwcomposer: Add fallback to client for layers flattening

Google recommends to delegate composition to GLES instead of HWC when
screen isn't updating to conserve power, as stated on page
https://source.android.com/devices/graphics/implement-hwc.

Current implementation of hwcomposer has flattening of layers if after
some time there were no updates of frames, but it uses writeback
connector. Not every device has a support of writeback feature, so
some sort of fallback should be provided.

It is possible to fallback to client composition in case if writeback
isn't available. This is used to reduce power consumption since
squashing layers into a single layer on GPU and then using that buffer
is more efficient than loading drm device.

Signed-off-by: Roman Kovalivskyi <roman.kovalivskyi@globallogic.com>

compositor/drmdisplaycompositor.cpp

diff --git a/compositor/drmdisplaycompositor.cpp b/compositor/drmdisplaycompositor.cpp
index e6f6922..401af48 100644
--- a/compositor/drmdisplaycompositor.cpp
+++ b/compositor/drmdisplaycompositor.cpp
@@ -63,7 +63,8 @@
       dump_frames_composited_(0),
       dump_last_timestamp_ns_(0),
       flatten_countdown_(FLATTEN_COUNTDOWN_INIT),
-      writeback_fence_(-1) {
+      writeback_fence_(-1),
+      flattening_state_(FlatteningState::kNone) {
   struct timespec ts;
   if (clock_gettime(CLOCK_MONOTONIC, &ts))
     return;
@@ -143,6 +144,15 @@
   return comp;
 }
 
+FlatteningState DrmDisplayCompositor::GetFlatteningState() const {
+  return flattening_state_;
+}
+
+bool DrmDisplayCompositor::ShouldFlattenOnClient() const {
+  return flattening_state_ == FlatteningState::kClientRequested ||
+         flattening_state_ == FlatteningState::kClientDone;
+}
+
 std::tuple<uint32_t, uint32_t, int>
 DrmDisplayCompositor::GetActiveModeResolution() {
   DrmDevice *drm = resource_manager_->GetDrmDevice(display_);
@@ -605,6 +615,11 @@
   active_composition_.swap(composition);
 
   flatten_countdown_ = FLATTEN_COUNTDOWN_INIT;
+  if (flattening_state_ != FlatteningState::kClientRequested) {
+    flattening_state_ = FlatteningState::kNone;
+  } else {
+    flattening_state_ = FlatteningState::kClientDone;
+  }
   vsync_worker_.VSyncControl(!writeback);
 }
 
@@ -761,6 +776,35 @@
   return 0;
 }
 
+bool DrmDisplayCompositor::IsFlatteningNeeded() const {
+  return CountdownExpired() && active_composition_->layers().size() >= 2;
+}
+
+int DrmDisplayCompositor::FlattenOnClient() {
+  if (refresh_display_cb_) {
+    {
+      AutoLock lock(&lock_, __func__);
+      if (!IsFlatteningNeeded()) {
+        if (flattening_state_ != FlatteningState::kClientDone) {
+          ALOGV("Flattening is not needed");
+          flattening_state_ = FlatteningState::kNotNeeded;
+        }
+        return -EALREADY;
+      }
+    }
+
+    ALOGV(
+        "No writeback connector available, "
+        "falling back to client composition");
+    flattening_state_ = FlatteningState::kClientRequested;
+    refresh_display_cb_(display_);
+    return 0;
+  } else {
+    ALOGV("No writeback connector available");
+    return -EINVAL;
+  }
+}
+
 // Flatten a scene by enabling the writeback connector attached
 // to the same CRTC as the one driving the display.
 int DrmDisplayCompositor::FlattenSerial(DrmConnector *writeback_conn) {
@@ -776,8 +820,9 @@
   int ret = lock.Lock();
   if (ret)
     return ret;
-  if (!CountdownExpired() || active_composition_->layers().size() < 2) {
+  if (!IsFlatteningNeeded()) {
     ALOGV("Flattening is not needed");
+    flattening_state_ = FlatteningState::kNotNeeded;
     return -EALREADY;
   }
 
@@ -884,8 +929,9 @@
   ret = lock.Lock();
   if (ret)
     return ret;
-  if (!CountdownExpired() || active_composition_->layers().size() < 2) {
+  if (!IsFlatteningNeeded()) {
     ALOGV("Flattening is not needed");
+    flattening_state_ = FlatteningState::kNotNeeded;
     return -EALREADY;
   }
   DrmCrtc *crtc = active_composition_->crtc();
@@ -955,13 +1001,16 @@
   DrmConnector *writeback_conn = resource_manager_->AvailableWritebackConnector(
       display_);
   if (!active_composition_ || !writeback_conn) {
-    ALOGV("No writeback connector available");
-    return -EINVAL;
+    // Try to fallback to GPU composition on client, since it is more
+    // power-efficient than composition on device side
+    return FlattenOnClient();
   }
 
   if (writeback_conn->display() != display_) {
+    flattening_state_ = FlatteningState::kConcurrent;
     return FlattenConcurrent(writeback_conn);
   } else {
+    flattening_state_ = FlatteningState::kSerial;
     return FlattenSerial(writeback_conn);
   }