commit 8053f2eddb4dd0168bb6328219a7fa612c3eac04
author Drew Davenport <ddavenport@google.com> Wed Oct 02 13:44:41 2024 -0600
committer Drew Davenport <ddavenport@google.com> Tue Oct 08 09:36:41 2024 -0600
tree 6f5c26e3598210704cdbc0959eccfc4ea0105e82
parent 3f4469f92ae7de6ab9fe7ac3f9c920b09eb53c27

drm_hwcomposer: Calculate vsync period consistently

Calculating the vsync period can yield different results depending on
floating point precision and ordering of operations.

Calcuate the vsync period in one place for consistency.

Change-Id: I968e4976ec5d546f66ffe3e0f7dd404cd934a60c
Signed-off-by: Drew Davenport <ddavenport@google.com>

drm/DrmMode.h

diff --git a/drm/DrmMode.h b/drm/DrmMode.h
index c5790a5..5450daf 100644
--- a/drm/DrmMode.h
+++ b/drm/DrmMode.h
@@ -48,6 +48,12 @@
            (float)(mode_.vtotal * mode_.htotal) * 1000.0F;
   }
 
+  auto GetVSyncPeriodNs() const {
+    static const int kNanosecondsPerSecond = 1E9;
+    return static_cast<int32_t>(kNanosecondsPerSecond *
+                                double(1 / GetVRefresh()));
+  }
+
   auto GetName() const {
     return std::string(mode_.name) + "@" + std::to_string(GetVRefresh());
   }

hwc2_device/HwcDisplay.cpp

diff --git a/hwc2_device/HwcDisplay.cpp b/hwc2_device/HwcDisplay.cpp
index 36333d2..9a9761b 100644
--- a/hwc2_device/HwcDisplay.cpp
+++ b/hwc2_device/HwcDisplay.cpp
@@ -320,7 +320,7 @@
       break;
     case HWC2::Attribute::VsyncPeriod:
       // in nanoseconds
-      *value = static_cast<int>(1E9 / hwc_config.mode.GetVRefresh());
+      *value = hwc_config.mode.GetVSyncPeriodNs();
       break;
     case HWC2::Attribute::DpiY:
       // ideally this should be vdisplay/mm_heigth, however mm_height

hwc3/ComposerClient.cpp

diff --git a/hwc3/ComposerClient.cpp b/hwc3/ComposerClient.cpp
index eb4e683..2efce8f 100644
--- a/hwc3/ComposerClient.cpp
+++ b/hwc3/ComposerClient.cpp
@@ -972,15 +972,13 @@
 
   const HwcDisplayConfigs& configs = display->GetDisplayConfigs();
   for (const auto& [id, config] : configs.hwc_configs) {
-    static const int kNanosecondsPerSecond = 1E9;
     configurations->emplace_back(
         DisplayConfiguration{.configId = static_cast<int32_t>(config.id),
                              .width = config.mode.GetRawMode().hdisplay,
                              .height = config.mode.GetRawMode().vdisplay,
                              .configGroup = static_cast<int32_t>(
                                  config.group_id),
-                             .vsyncPeriod = static_cast<int>(kNanosecondsPerSecond * double(
-                                 1 / config.mode.GetVRefresh()))});
+                             .vsyncPeriod = config.mode.GetVSyncPeriodNs()});
 
     if (configs.mm_width != 0) {
       // ideally this should be vdisplay/mm_heigth, however mm_height