diff --git a/backend/backend.cpp b/backend/backend.cpp
new file mode 100644
index 0000000..08ee5a7
--- /dev/null
+++ b/backend/backend.cpp
@@ -0,0 +1,136 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "backend.h"
+#include "backendmanager.h"
+#include "drmhwctwo.h"
+
+namespace android {
+
+HWC2::Error Backend::ValidateDisplay(DrmHwcTwo::HwcDisplay *display,
+                                     uint32_t *num_types,
+                                     uint32_t *num_requests) {
+  *num_types = 0;
+  *num_requests = 0;
+  size_t avail_planes = display->primary_planes().size() +
+                        display->overlay_planes().size();
+
+  /*
+   * If more layers then planes, save one plane
+   * for client composited layers
+   */
+  if (avail_planes < display->layers().size())
+    avail_planes--;
+
+  std::map<uint32_t, DrmHwcTwo::HwcLayer *> z_map, z_map_tmp;
+  uint32_t z_index = 0;
+  // First create a map of layers and z_order values
+  for (std::pair<const hwc2_layer_t, DrmHwcTwo::HwcLayer> &l :
+       display->layers())
+    z_map_tmp.emplace(std::make_pair(l.second.z_order(), &l.second));
+  // normalise the map so that the lowest z_order layer has key 0
+  for (std::pair<const uint32_t, DrmHwcTwo::HwcLayer *> &l : z_map_tmp)
+    z_map.emplace(std::make_pair(z_index++, l.second));
+
+  uint32_t total_pixops = display->CalcPixOps(z_map, 0, z_map.size());
+  uint32_t gpu_pixops = 0;
+
+  int client_start = -1, client_size = 0;
+
+  if (display->compositor().ShouldFlattenOnClient()) {
+    client_start = 0;
+    client_size = z_map.size();
+    display->MarkValidated(z_map, client_start, client_size);
+  } else {
+    std::tie(client_start, client_size) = GetClientLayers(display, z_map);
+
+    int extra_client = (z_map.size() - client_size) - avail_planes;
+    if (extra_client > 0) {
+      int start = 0, steps;
+      if (client_size != 0) {
+        int prepend = std::min(client_start, extra_client);
+        int append = std::min(int(z_map.size() - (client_start + client_size)),
+                              extra_client);
+        start = client_start - prepend;
+        client_size += extra_client;
+        steps = 1 + std::min(std::min(append, prepend),
+                             int(z_map.size()) - (start + client_size));
+      } else {
+        client_size = extra_client;
+        steps = 1 + z_map.size() - extra_client;
+      }
+
+      gpu_pixops = INT_MAX;
+      for (int i = 0; i < steps; i++) {
+        uint32_t po = display->CalcPixOps(z_map, start + i, client_size);
+        if (po < gpu_pixops) {
+          gpu_pixops = po;
+          client_start = start + i;
+        }
+      }
+    }
+
+    display->MarkValidated(z_map, client_start, client_size);
+
+    bool testing_needed = !(client_start == 0 && client_size == z_map.size());
+
+    if (testing_needed &&
+        display->CreateComposition(true) != HWC2::Error::None) {
+      ++display->total_stats().failed_kms_validate_;
+      gpu_pixops = total_pixops;
+      client_size = z_map.size();
+      display->MarkValidated(z_map, 0, client_size);
+    }
+  }
+
+  *num_types = client_size;
+
+  display->total_stats().frames_flattened_ = display->compositor()
+                                                 .GetFlattenedFramesCount();
+  display->total_stats().gpu_pixops_ += gpu_pixops;
+  display->total_stats().total_pixops_ += total_pixops;
+
+  return *num_types ? HWC2::Error::HasChanges : HWC2::Error::None;
+}
+
+std::tuple<int, int> Backend::GetClientLayers(
+    DrmHwcTwo::HwcDisplay *display,
+    const std::map<uint32_t, DrmHwcTwo::HwcLayer *> &z_map) {
+  int client_start = -1, client_size = 0;
+
+  for (auto & [ z_order, layer ] : z_map) {
+    if (IsClientLayer(display, layer)) {
+      if (client_start < 0)
+        client_start = z_order;
+      client_size = (z_order - client_start) + 1;
+    }
+  }
+
+  return std::make_tuple(client_start, client_size);
+}
+
+bool Backend::IsClientLayer(DrmHwcTwo::HwcDisplay *display,
+                            DrmHwcTwo::HwcLayer *layer) {
+  return !display->HardwareSupportsLayerType(layer->sf_type()) ||
+         !display->importer()->CanImportBuffer(layer->buffer()) ||
+         display->color_transform_hint() != HAL_COLOR_TRANSFORM_IDENTITY ||
+         (layer->RequireScalingOrPhasing() &&
+          display->resource_manager()->ForcedScalingWithGpu());
+}
+
+REGISTER_BACKEND("generic", Backend);
+
+}  // namespace android