drm_hwcomposer: Remove writeback-based flattening logic

Writeback Pros:
a. Very tiny reduction in power consumption required for
   rendering the composition compared to CLIENT-based flattening.

Writeback Cons:
a. A lot of extra code. High maintenance cost(effort).
   Nobody tests it as for now.
b. Writeback isn't implemented by the set of KMS drivers
c. Require separate memory buffer to be allocated

Part of: https://gitlab.freedesktop.org/drm-hwcomposer/drm-hwcomposer/-/issues/47
Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>

2 files changed, 6 insertions, 403 deletions

diff --git a/compositor/DrmDisplayCompositor.cpp b/compositor/DrmDisplayCompositor.cpp
index 8d96d0e..2cc0da5 100644
--- a/compositor/DrmDisplayCompositor.cpp
+++ b/compositor/DrmDisplayCompositor.cpp
@@ -37,8 +37,6 @@
 #include "drm/DrmPlane.h"
 #include "utils/autolock.h"
 
-static const uint32_t kWaitWritebackFence = 100;  // ms
-
 namespace android {
 
 std::ostream &operator<<(std::ostream &str, FlatteningState state) {
@@ -73,7 +71,6 @@ DrmDisplayCompositor::DrmDisplayCompositor()
       dump_frames_composited_(0),
       dump_last_timestamp_ns_(0),
       flatten_countdown_(FLATTEN_COUNTDOWN_INIT),
-      writeback_fence_(-1),
       flattening_state_(FlatteningState::kNone),
       frames_flattened_(0) {
   struct timespec ts {};
@@ -216,49 +213,8 @@ int DrmDisplayCompositor::DisablePlanes(DrmDisplayComposition *display_comp) {
   return 0;
 }
 
-int DrmDisplayCompositor::SetupWritebackCommit(drmModeAtomicReqPtr pset,
-                                               uint32_t crtc_id,
-                                               DrmConnector *writeback_conn,
-                                               DrmHwcBuffer *writeback_buffer) {
-  int ret = 0;
-  if (writeback_conn->writeback_fb_id().id() == 0 ||
-      writeback_conn->writeback_out_fence().id() == 0) {
-    ALOGE("Writeback properties don't exit");
-    return -EINVAL;
-  }
-  if ((*writeback_buffer)->fb_id == 0) {
-    ALOGE("Invalid writeback buffer");
-    return -EINVAL;
-  }
-  ret = drmModeAtomicAddProperty(pset, writeback_conn->id(),
-                                 writeback_conn->writeback_fb_id().id(),
-                                 (*writeback_buffer)->fb_id);
-  if (ret < 0) {
-    ALOGE("Failed to add writeback_fb_id");
-    return ret;
-  }
-  ret = drmModeAtomicAddProperty(pset, writeback_conn->id(),
-                                 writeback_conn->writeback_out_fence().id(),
-                                 (uint64_t)&writeback_fence_);
-  if (ret < 0) {
-    ALOGE("Failed to add writeback_out_fence");
-    return ret;
-  }
-
-  ret = drmModeAtomicAddProperty(pset, writeback_conn->id(),
-                                 writeback_conn->crtc_id_property().id(),
-                                 crtc_id);
-  if (ret < 0) {
-    ALOGE("Failed to  attach writeback");
-    return ret;
-  }
-  return 0;
-}
-
 int DrmDisplayCompositor::CommitFrame(DrmDisplayComposition *display_comp,
-                                      bool test_only,
-                                      DrmConnector *writeback_conn,
-                                      DrmHwcBuffer *writeback_buffer) {
+                                      bool test_only) {
   ATRACE_CALL();
 
   int ret = 0;
@@ -286,18 +242,6 @@ int DrmDisplayCompositor::CommitFrame(DrmDisplayComposition *display_comp,
     return -ENOMEM;
   }
 
-  if (writeback_buffer != nullptr) {
-    if (writeback_conn == nullptr) {
-      ALOGE("Invalid arguments requested writeback without writeback conn");
-      return -EINVAL;
-    }
-    ret = SetupWritebackCommit(pset, crtc->id(), writeback_conn,
-                               writeback_buffer);
-    if (ret < 0) {
-      ALOGE("Failed to Setup Writeback Commit ret = %d", ret);
-      return ret;
-    }
-  }
   if (crtc->out_fence_ptr_property().id() != 0) {
     ret = drmModeAtomicAddProperty(pset, crtc->id(),
                                    crtc->out_fence_ptr_property().id(),
@@ -661,22 +605,16 @@ void DrmDisplayCompositor::ClearDisplay() {
     return;
 
   active_composition_.reset(nullptr);
-  vsync_worker_.VSyncControl(false);
 }
 
 void DrmDisplayCompositor::ApplyFrame(
-    std::unique_ptr<DrmDisplayComposition> composition, int status,
-    bool writeback) {
+    std::unique_ptr<DrmDisplayComposition> composition, int status) {
   AutoLock lock(&lock_, __func__);
   if (lock.Lock())
     return;
   int ret = status;
 
   if (!ret) {
-    if (writeback && !CountdownExpired()) {
-      ALOGE("Abort playing back scene");
-      return;
-    }
     ret = CommitFrame(composition.get(), false);
   }
 
@@ -697,7 +635,7 @@ void DrmDisplayCompositor::ApplyFrame(
   } else {
     SetFlattening(FlatteningState::kClientDone);
   }
-  vsync_worker_.VSyncControl(!writeback);
+  vsync_worker_.VSyncControl(true);
 }
 
 int DrmDisplayCompositor::ApplyComposition(
@@ -747,118 +685,10 @@ int DrmDisplayCompositor::TestComposition(DrmDisplayComposition *composition) {
   return CommitFrame(composition, true);
 }
 
-// Flatten a scene on the display by using a writeback connector
-// and returns the composition result as a DrmHwcLayer.
-int DrmDisplayCompositor::FlattenOnDisplay(
-    std::unique_ptr<DrmDisplayComposition> &src, DrmConnector *writeback_conn,
-    DrmMode &src_mode, DrmHwcLayer *writeback_layer) {
-  int ret = 0;
-  DrmDevice *drm = resource_manager_->GetDrmDevice(display_);
-  ret = writeback_conn->UpdateModes();
-  if (ret) {
-    ALOGE("Failed to update modes %d", ret);
-    return ret;
-  }
-  for (const DrmMode &mode : writeback_conn->modes()) {
-    if (mode.h_display() == src_mode.h_display() &&
-        mode.v_display() == src_mode.v_display()) {
-      mode_.mode = mode;
-      if (mode_.blob_id)
-        drm->DestroyPropertyBlob(mode_.blob_id);
-      std::tie(ret, mode_.blob_id) = CreateModeBlob(mode_.mode);
-      if (ret) {
-        ALOGE("Failed to create mode blob for display %d", display_);
-        return ret;
-      }
-      mode_.needs_modeset = true;
-      break;
-    }
-  }
-  if (mode_.blob_id <= 0) {
-    ALOGE("Failed to find similar mode");
-    return -EINVAL;
-  }
-
-  DrmCrtc *crtc = drm->GetCrtcForDisplay(display_);
-  if (!crtc) {
-    ALOGE("Failed to find crtc for display %d", display_);
-    return -EINVAL;
-  }
-  // TODO(nobody) what happens if planes could go to both CRTCs, I don't think
-  // it's handled anywhere
-  std::vector<DrmPlane *> primary_planes;
-  std::vector<DrmPlane *> overlay_planes;
-  for (auto &plane : drm->planes()) {
-    if (!plane->GetCrtcSupported(*crtc))
-      continue;
-    if (plane->type() == DRM_PLANE_TYPE_PRIMARY)
-      primary_planes.push_back(plane.get());
-    else if (plane->type() == DRM_PLANE_TYPE_OVERLAY)
-      overlay_planes.push_back(plane.get());
-  }
-
-  ret = src->Plan(&primary_planes, &overlay_planes);
-  if (ret) {
-    ALOGE("Failed to plan the composition ret = %d", ret);
-    return ret;
-  }
-
-  // Disable the planes we're not using
-  for (auto i = primary_planes.begin(); i != primary_planes.end();) {
-    src->AddPlaneDisable(*i);
-    i = primary_planes.erase(i);
-  }
-  for (auto i = overlay_planes.begin(); i != overlay_planes.end();) {
-    src->AddPlaneDisable(*i);
-    i = overlay_planes.erase(i);
-  }
-
-  AutoLock lock(&lock_, __func__);
-  ret = lock.Lock();
-  if (ret)
-    return ret;
-  DrmFramebuffer *writeback_fb = &framebuffers_[framebuffer_index_];
-  framebuffer_index_ = (framebuffer_index_ + 1) % DRM_DISPLAY_BUFFERS;
-  if (!writeback_fb->Allocate(mode_.mode.h_display(), mode_.mode.v_display())) {
-    ALOGE("Failed to allocate writeback buffer");
-    return -ENOMEM;
-  }
-  DrmHwcBuffer *writeback_buffer = &writeback_layer->buffer;
-  writeback_layer->sf_handle = writeback_fb->buffer()->handle;
-  ret = writeback_layer->ImportBuffer(
-      resource_manager_->GetImporter(display_).get());
-  if (ret) {
-    ALOGE("Failed to import writeback buffer");
-    return ret;
-  }
-
-  ret = CommitFrame(src.get(), true, writeback_conn, writeback_buffer);
-  if (ret) {
-    ALOGE("Atomic check failed");
-    return ret;
-  }
-  ret = CommitFrame(src.get(), false, writeback_conn, writeback_buffer);
-  if (ret) {
-    ALOGE("Atomic commit failed");
-    return ret;
-  }
-
-  ret = sync_wait(writeback_fence_, kWaitWritebackFence);
-  writeback_layer->acquire_fence.Set(writeback_fence_);
-  writeback_fence_ = -1;
-  if (ret) {
-    ALOGE("Failed to wait on writeback fence");
-    return ret;
-  }
-  return 0;
-}
-
 void DrmDisplayCompositor::SetFlattening(FlatteningState new_state) {
   if (flattening_state_ != new_state) {
     switch (flattening_state_) {
       case FlatteningState::kClientDone:
-      case FlatteningState::kConcurrent:
-      case FlatteningState::kSerial:
         ++frames_flattened_;
         break;
       case FlatteningState::kClientRequested:
@@ -901,214 +731,8 @@ int DrmDisplayCompositor::FlattenOnClient() {
   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) {
-  ALOGV("FlattenSerial by enabling writeback connector to the same crtc");
-  // Flattened composition with only one layer that is obtained
-  // using the writeback connector
-  std::unique_ptr<DrmDisplayComposition>
-      writeback_comp = CreateInitializedComposition();
-  if (!writeback_comp)
-    return -EINVAL;
-
-  AutoLock lock(&lock_, __func__);
-  int ret = lock.Lock();
-  if (ret)
-    return ret;
-  if (!IsFlatteningNeeded()) {
-    ALOGV("Flattening is not needed");
-    SetFlattening(FlatteningState::kNotNeeded);
-    return -EALREADY;
-  }
-
-  DrmFramebuffer *writeback_fb = &framebuffers_[framebuffer_index_];
-  framebuffer_index_ = (framebuffer_index_ + 1) % DRM_DISPLAY_BUFFERS;
-  lock.Unlock();
-
-  if (!writeback_fb->Allocate(mode_.mode.h_display(), mode_.mode.v_display())) {
-    ALOGE("Failed to allocate writeback buffer");
-    return -ENOMEM;
-  }
-  writeback_comp->layers().emplace_back();
-
-  DrmHwcLayer &writeback_layer = writeback_comp->layers().back();
-  writeback_layer.sf_handle = writeback_fb->buffer()->handle;
-  writeback_layer.source_crop = {0, 0, (float)mode_.mode.h_display(),
-                                 (float)mode_.mode.v_display()};
-  writeback_layer.display_frame = {0, 0, (int)mode_.mode.h_display(),
-                                   (int)mode_.mode.v_display()};
-  ret = writeback_layer.ImportBuffer(
-      resource_manager_->GetImporter(display_).get());
-  if (ret || writeback_comp->layers().size() != 1) {
-    ALOGE("Failed to import writeback buffer");
-    return ret;
-  }
-
-  drmModeAtomicReqPtr pset = drmModeAtomicAlloc();
-  if (!pset) {
-    ALOGE("Failed to allocate property set");
-    return -ENOMEM;
-  }
-  DrmDevice *drm = resource_manager_->GetDrmDevice(display_);
-  DrmCrtc *crtc = drm->GetCrtcForDisplay(display_);
-  if (!crtc) {
-    ALOGE("Failed to find crtc for display %d", display_);
-    return -EINVAL;
-  }
-  ret = SetupWritebackCommit(pset, crtc->id(), writeback_conn,
-                             &writeback_layer.buffer);
-  if (ret < 0) {
-    ALOGE("Failed to Setup Writeback Commit");
-    return ret;
-  }
-  ret = drmModeAtomicCommit(drm->fd(), pset, 0, drm);
-  if (ret) {
-    ALOGE("Failed to enable writeback %d", ret);
-    return ret;
-  }
-  ret = sync_wait(writeback_fence_, kWaitWritebackFence);
-  writeback_layer.acquire_fence.Set(writeback_fence_);
-  writeback_fence_ = -1;
-  if (ret) {
-    ALOGE("Failed to wait on writeback fence");
-    return ret;
-  }
-
-  DrmCompositionPlane squashed_comp(DrmCompositionPlane::Type::kLayer, nullptr,
-                                    crtc);
-  for (auto &drmplane : drm->planes()) {
-    if (!drmplane->GetCrtcSupported(*crtc))
-      continue;
-    if (!squashed_comp.plane() && drmplane->type() == DRM_PLANE_TYPE_PRIMARY)
-      squashed_comp.set_plane(drmplane.get());
-    else
-      writeback_comp->AddPlaneDisable(drmplane.get());
-  }
-  squashed_comp.source_layers().push_back(0);
-  ret = writeback_comp->AddPlaneComposition(std::move(squashed_comp));
-  if (ret) {
-    ALOGE("Failed to add flatten scene");
-    return ret;
-  }
-
-  ApplyFrame(std::move(writeback_comp), 0, true);
-  return 0;
-}
-
-// Flatten a scene by using a crtc which works concurrent with
-// the one driving the display.
-int DrmDisplayCompositor::FlattenConcurrent(DrmConnector *writeback_conn) {
-  ALOGV("FlattenConcurrent by using an unused crtc/display");
-  int ret = 0;
-  DrmDisplayCompositor drmdisplaycompositor;
-  ret = drmdisplaycompositor.Init(resource_manager_, writeback_conn->display());
-  if (ret) {
-    ALOGE("Failed to init  drmdisplaycompositor = %d", ret);
-    return ret;
-  }
-  // Copy of the active_composition, needed because of two things:
-  // 1) Not to hold the lock for the whole time we are accessing
-  //    active_composition
-  // 2) It will be committed on a crtc that might not be on the same
-  //     dri node, so buffers need to be imported on the right node.
-  std::unique_ptr<DrmDisplayComposition>
-      copy_comp = drmdisplaycompositor.CreateInitializedComposition();
-
-  // Writeback composition that will be committed to the display.
-  std::unique_ptr<DrmDisplayComposition>
-      writeback_comp = CreateInitializedComposition();
-
-  if (!copy_comp || !writeback_comp)
-    return -EINVAL;
-  AutoLock lock(&lock_, __func__);
-  ret = lock.Lock();
-  if (ret)
-    return ret;
-  if (!IsFlatteningNeeded()) {
-    ALOGV("Flattening is not needed");
-    SetFlattening(FlatteningState::kNotNeeded);
-    return -EALREADY;
-  }
-  DrmCrtc *crtc = active_composition_->crtc();
-
-  std::vector<DrmHwcLayer> copy_layers;
-  for (DrmHwcLayer &src_layer : active_composition_->layers()) {
-    DrmHwcLayer copy;
-    ret = copy.InitFromDrmHwcLayer(&src_layer,
-                                   resource_manager_
-                                       ->GetImporter(writeback_conn->display())
-                                       .get());
-    if (ret) {
-      ALOGE("Failed to import buffer ret = %d", ret);
-      return -EINVAL;
-    }
-    copy_layers.emplace_back(std::move(copy));
-  }
-  ret = copy_comp->SetLayers(copy_layers.data(), copy_layers.size(), true);
-  if (ret) {
-    ALOGE("Failed to set copy_comp layers");
-    return ret;
-  }
-
-  lock.Unlock();
-  DrmHwcLayer writeback_layer;
-  ret = drmdisplaycompositor.FlattenOnDisplay(copy_comp, writeback_conn,
-                                              mode_.mode, &writeback_layer);
-  if (ret) {
-    ALOGE("Failed to flatten on display ret = %d", ret);
-    return ret;
-  }
-
-  DrmCompositionPlane squashed_comp(DrmCompositionPlane::Type::kLayer, nullptr,
-                                    crtc);
-  for (auto &drmplane : resource_manager_->GetDrmDevice(display_)->planes()) {
-    if (!drmplane->GetCrtcSupported(*crtc))
-      continue;
-    if (drmplane->type() == DRM_PLANE_TYPE_PRIMARY)
-      squashed_comp.set_plane(drmplane.get());
-    else
-      writeback_comp->AddPlaneDisable(drmplane.get());
-  }
-  writeback_comp->layers().emplace_back();
-  DrmHwcLayer &next_layer = writeback_comp->layers().back();
-  next_layer.sf_handle = writeback_layer.get_usable_handle();
-  next_layer.blending = DrmHwcBlending::kPreMult;
-  next_layer.source_crop = {0, 0, (float)mode_.mode.h_display(),
-                            (float)mode_.mode.v_display()};
-  next_layer.display_frame = {0, 0, (int)mode_.mode.h_display(),
-                              (int)mode_.mode.v_display()};
-  ret = next_layer.ImportBuffer(resource_manager_->GetImporter(display_).get());
-  if (ret) {
-    ALOGE("Failed to import framebuffer for display %d", ret);
-    return ret;
-  }
-  squashed_comp.source_layers().push_back(0);
-  ret = writeback_comp->AddPlaneComposition(std::move(squashed_comp));
-  if (ret) {
-    ALOGE("Failed to add plane composition %d", ret);
-    return ret;
-  }
-  ApplyFrame(std::move(writeback_comp), 0, true);
-  return ret;
-}
-
 int DrmDisplayCompositor::FlattenActiveComposition() {
-  DrmConnector *writeback_conn = resource_manager_->AvailableWritebackConnector(
-      display_);
-  if (!active_composition_ || !writeback_conn) {
-    // 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_) {
-    SetFlattening(FlatteningState::kConcurrent);
-    return FlattenConcurrent(writeback_conn);
-  }
-
-  SetFlattening(FlatteningState::kSerial);
-  return FlattenSerial(writeback_conn);
+  return FlattenOnClient();
 }
 
 bool DrmDisplayCompositor::CountdownExpired() const {
diff --git a/compositor/DrmDisplayCompositor.h b/compositor/DrmDisplayCompositor.h
index 92dadca..8660a6d 100644
--- a/compositor/DrmDisplayCompositor.h
+++ b/compositor/DrmDisplayCompositor.h
@@ -26,16 +26,11 @@
 #include <tuple>
 
 #include "DrmDisplayComposition.h"
-#include "DrmFramebuffer.h"
 #include "Planner.h"
 #include "drm/ResourceManager.h"
 #include "drm/VSyncWorker.h"
 #include "drmhwcomposer.h"
 
-// One for the front, one for the back, and one for cases where we need to
-// squash a frame that the hw can't display with hw overlays.
-#define DRM_DISPLAY_BUFFERS 3
-
 // If a scene is still for this number of vblanks flatten it to reduce power
 // consumption.
 #define FLATTEN_COUNTDOWN_INIT 60
@@ -47,8 +42,6 @@ enum class FlatteningState {
   kNotNeeded,
   kClientRequested,
   kClientDone,
-  kSerial,
-  kConcurrent
 };
 
 std::ostream &operator<<(std::ostream &str, FlatteningState state);
@@ -106,27 +99,17 @@ class DrmDisplayCompositor {
   static const int kAcquireWaitTries = 5;
   static const int kAcquireWaitTimeoutMs = 100;
 
-  int CommitFrame(DrmDisplayComposition *display_comp, bool test_only,
-                  DrmConnector *writeback_conn = NULL,
-                  DrmHwcBuffer *writeback_buffer = NULL);
-  int SetupWritebackCommit(drmModeAtomicReqPtr pset, uint32_t crtc_id,
-                           DrmConnector *writeback_conn,
-                           DrmHwcBuffer *writeback_buffer);
+  int CommitFrame(DrmDisplayComposition *display_comp, bool test_only);
   int ApplyDpms(DrmDisplayComposition *display_comp);
   int DisablePlanes(DrmDisplayComposition *display_comp);
 
   void ApplyFrame(std::unique_ptr<DrmDisplayComposition> composition,
-                  int status, bool writeback = false);
+                  int status);
 
   void SetFlattening(FlatteningState new_state);
   bool IsFlatteningNeeded() const;
   int FlattenActiveComposition();
   int FlattenOnClient();
-  int FlattenSerial(DrmConnector *writeback_conn);
-  int FlattenConcurrent(DrmConnector *writeback_conn);
-  int FlattenOnDisplay(std::unique_ptr<DrmDisplayComposition> &src,
-                       DrmConnector *writeback_conn, DrmMode &src_mode,
-                       DrmHwcLayer *writeback_layer);
 
   bool CountdownExpired() const;
 
@@ -143,9 +126,6 @@ class DrmDisplayCompositor {
 
   ModeState mode_;
 
-  int framebuffer_index_{};
-  DrmFramebuffer framebuffers_[DRM_DISPLAY_BUFFERS];
-
   // mutable since we need to acquire in Dump()
   mutable pthread_mutex_t lock_{};
 
@@ -156,7 +136,6 @@ class DrmDisplayCompositor {
   VSyncWorker vsync_worker_;
   int64_t flatten_countdown_;
   std::unique_ptr<Planner> planner_;
-  int writeback_fence_;
 
   FlatteningState flattening_state_;
   uint32_t frames_flattened_;