commit f638348b22e96e208badb71de52a860d201ee2fb
author Drew Davenport <ddavenport@google.com> Fri Feb 21 10:05:39 2025 -0700
committer Drew Davenport <ddavenport@google.com> Fri Mar 14 11:38:40 2025 -0600
tree fbadd16cc9ed4d2d4aa38453dca33e6fcf88aefd
parent 609c353553bb3f172d21394b8bf62b3bace09579

drm_hwcomposer: Support DisplayCommand.expectedPresentTime

DisplayCommand.expectedPresentTime indicates that the HWC should present
the composition as close to the desired time as possible. It may be that
the desired time is some number of vsync periods in the future.

A drm atomic commit will always present at the next vsync, and there is
no mechanism for userspace to indicate a desired present time.

Lacking a kernel uAPI to support this, an alternative is to sleep in
userspace until the next expected vsync aligns with the expected present
time.

Change-Id: Iad703eed9b0e459194f895339dd604990875f157
Signed-off-by: Drew Davenport <ddavenport@google.com>

hwc3/ComposerClient.cpp

diff --git a/hwc3/ComposerClient.cpp b/hwc3/ComposerClient.cpp
index 4dafb48..368d5eb 100644
--- a/hwc3/ComposerClient.cpp
+++ b/hwc3/ComposerClient.cpp
@@ -152,6 +152,14 @@
   return AidlToSampleRange(dataspace->dataspace);
 }
 
+std::optional<int64_t> AidlToPresentTimeNs(
+    const std::optional<ClockMonotonicTimestamp>& expected_present_time) {
+  if (!expected_present_time || expected_present_time->timestampNanos == 0) {
+    return std::nullopt;
+  }
+  return expected_present_time->timestampNanos;
+}
+
 bool IsSupportedCompositionType(
     const std::optional<ParcelableComposition> composition) {
   if (!composition) {
@@ -725,6 +733,8 @@
     cmd_result_writer_->AddChanges(changes);
     auto hwc3_display = DrmHwcThree::GetHwc3Display(*display);
     hwc3_display->must_validate = false;
+    hwc3_display->desired_present_time = AidlToPresentTimeNs(
+        command.expectedPresentTime);
 
     // TODO: DisplayRequests are not implemented.
   }
@@ -749,9 +759,12 @@
       cmd_result_writer_->AddError(hwc3::Error::kNotValidated);
       return;
     }
+
     ::android::SharedFd present_fence;
     std::vector<HwcDisplay::ReleaseFence> release_fences;
-    bool ret = display->PresentStagedComposition(present_fence, release_fences);
+    bool ret = display->PresentStagedComposition(hwc3_display
+                                                     ->desired_present_time,
+                                                 present_fence, release_fences);
 
     if (!ret) {
       cmd_result_writer_->AddError(hwc3::Error::kBadDisplay);