eglfs: Report the QScreen refresh rate from eglfs

For KMS we can always know the correct rate so report it from the backend's custom
screen implementation.

For the rest, query from the framebuffer. If the fb driver publishes the timings then
we can calculate the vertical refresh rate from them. If not, default to 60.

Task-number: QTBUG-44971
Change-Id: I854a34e7c0d652790cc2ac967715828ec76f5733
Reviewed-by: Andy Nichols <andy.nichols@theqtcompany.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/src/platformsupport/eglconvenience/qeglconvenience.cpp b/src/platformsupport/eglconvenience/qeglconvenience.cpp
index 011e2c2961..922455c96f 100644
--- a/src/platformsupport/eglconvenience/qeglconvenience.cpp
+++ b/src/platformsupport/eglconvenience/qeglconvenience.cpp
@@ -576,6 +576,33 @@ int q_screenDepthFromFb(int framebufferDevice)
     return depth;
 }
 
+qreal q_refreshRateFromFb(int framebufferDevice)
+{
+    static qreal rate = 0;
+
+#ifdef Q_OS_LINUX
+    if (rate == 0) {
+        if (framebufferDevice != -1) {
+            struct fb_var_screeninfo vinfo;
+            if (ioctl(framebufferDevice, FBIOGET_VSCREENINFO, &vinfo) != -1) {
+                const quint64 quot = quint64(vinfo.left_margin + vinfo.right_margin + vinfo.xres + vinfo.hsync_len)
+                    * quint64(vinfo.upper_margin + vinfo.lower_margin + vinfo.yres + vinfo.vsync_len)
+                    * vinfo.pixclock;
+                if (quot)
+                    rate = 1000000000000LLU / quot;
+            } else {
+                qWarning("eglconvenience: Could not query screen info");
+            }
+        }
+    }
+#endif
+
+    if (rate == 0)
+        rate = 60;
+
+    return rate;
+}
+
 #endif // Q_OS_UNIX
 
 QT_END_NAMESPACE