From d2cb445f4c3b677a004b3be1c931ae60cf1049e7 Mon Sep 17 00:00:00 2001
From: Martin Graesslin <mgraesslin@kde.org>
Date: Mon, 19 Oct 2015 08:13:04 +0000
Subject: [PATCH] Delay enabling vsync till first frame is rendered

According to the hwcomposer documentation:
"It is a (silent) error to have HWC_EVENT_VSYNC enabled when calling
hwc_composer_device.set(..., 0, 0, 0) (screen off)".

Because of that we may not enable vsync directly after toggling the
output, but need to wait till after calling the set call.

Reviewed-by: Bhushan Shah
---
 backends/hwcomposer/hwcomposer_backend.cpp | 15 ++++++++++++++-
 backends/hwcomposer/hwcomposer_backend.h   |  2 ++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/backends/hwcomposer/hwcomposer_backend.cpp b/backends/hwcomposer/hwcomposer_backend.cpp
index 691749e6f4..8d5b706ac3 100644
--- a/backends/hwcomposer/hwcomposer_backend.cpp
+++ b/backends/hwcomposer/hwcomposer_backend.cpp
@@ -164,7 +164,10 @@ void HwcomposerBackend::toggleBlankOutput()
     }
     m_outputBlank = !m_outputBlank;
     m_device->blank(m_device, 0, m_outputBlank ? 1 : 0);
-    m_device->eventControl(m_device, 0, HWC_EVENT_VSYNC, m_outputBlank ? 0 : 1);
+    // only disable Vsycn, enable happens after next frame rendered
+    if (m_outputBlank) {
+         enableVSync(false);
+    }
     // enable/disable compositor repainting when blanked
     if (Compositor *compositor = Compositor::self()) {
         if (m_outputBlank) {
@@ -176,6 +179,15 @@ void HwcomposerBackend::toggleBlankOutput()
     }
 }
 
+void HwcomposerBackend::enableVSync(bool enable)
+{
+    if (m_hasVsync == enable) {
+        return;
+    }
+    const int result = m_device->eventControl(m_device, 0, HWC_EVENT_VSYNC, enable ? 1: 0);
+    m_hasVsync = enable && (result == 0);
+}
+
 HwcomposerWindow *HwcomposerBackend::createSurface()
 {
     return new HwcomposerWindow(this);
@@ -282,6 +294,7 @@ void HwcomposerWindow::present(HWComposerNativeWindowBuffer *buffer)
 
     err = device->set(device, 1, m_list);
     assert(err == 0);
+    m_backend->enableVSync(true);
     setFenceBufferFd(buffer, fblayer->releaseFenceFd);
 
     if (m_list[0]->retireFenceFd != -1) {
diff --git a/backends/hwcomposer/hwcomposer_backend.h b/backends/hwcomposer/hwcomposer_backend.h
index ca3da143ac..54b1bfa430 100644
--- a/backends/hwcomposer/hwcomposer_backend.h
+++ b/backends/hwcomposer/hwcomposer_backend.h
@@ -65,6 +65,7 @@ public:
     int refreshRate() const {
         return m_refreshRate;
     }
+    void enableVSync(bool enable);
 
 public Q_SLOTS:
     void vsync();
@@ -79,6 +80,7 @@ private:
     bool m_pageFlipPending = false;
     int m_refreshRate = 60000;
     QTimer *m_vsyncFailSafeTimer;
+    bool m_hasVsync = false;
 };
 
 class HwcomposerWindow : public HWComposerNativeWindow