drm_hwcomposer: Use most recently committed state

When preparing the properties for a commit, the state for the currently
active frame is used, rather than the last committed frame. This is
incorrect and could lead to a scenario such as:

- Frame N: commit enables plane 1
- Frame N+1: commit uses plane 1, 2, 3
- Frame N+2: if executed before staged_frame_state_ is moved to
    active_frame_state_, the new KmsState::used_framebuffers will be
    initialized to {1}
  - commit uses planes 1, 2
  - plane 3 is not disabled by the unused_planes code in CommitFrame

A similar problem exists for the KmsState::crtc_active_state.

To avoid this issue, always use the last committed state, regardless of
whether the previous frame has been presented or not.

Change-Id: I840b5b0ca3a3cf477882cacf6b1d5c0313ae80cf

drm/DrmAtomicStateManager.cpp

@@ -51,7 +51,11 @@ auto DrmAtomicStateManager::CommitFrame(AtomicCommitArgs &args) -> int {
   // NOLINTNEXTLINE(misc-const-correctness)
   ATRACE_CALL();
 
-  if (args.active && *args.active == active_frame_state_.crtc_active_state) {
+  // new_frame_state is initialized to the current frame state, so use it
+  // instead of active_frame_state_ or staged_frame_state_ to avoid races.
+  auto new_frame_state = NewFrameState();
+
+  if (args.active && *args.active == new_frame_state.crtc_active_state) {
     /* Don't set the same state twice */
     args.active.reset();
   }
@@ -61,13 +65,11 @@ auto DrmAtomicStateManager::CommitFrame(AtomicCommitArgs &args) -> int {
     return 0;
   }
 
-  if (!active_frame_state_.crtc_active_state) {
+  if (!new_frame_state.crtc_active_state) {
     /* Force activate display */
     args.active = true;
   }
 
-  auto new_frame_state = NewFrameState();
-
   auto *crtc = pipe_->crtc->Get();
 
   auto pset = MakeDrmModeAtomicReqUnique();

drm/DrmAtomicStateManager.h

@@ -108,7 +108,8 @@ class DrmAtomicStateManager {
   };
 
   KmsState NewFrameState() REQUIRES(main_mutex_) {
-    auto *prev_frame_state = &active_frame_state_;
+    auto *prev_frame_state = last_present_fence_ ? &staged_frame_state_
+                                                 : &active_frame_state_;
     return (KmsState){
         .used_planes = prev_frame_state->used_planes,
         .crtc_active_state = prev_frame_state->crtc_active_state,