From 79d78d814acad4e183e281aea9b131f396abe3fb Mon Sep 17 00:00:00 2001
From: Gatis Paeglis <gatis.paeglis@qt.io>
Date: Thu, 7 Dec 2017 11:49:49 +0100
Subject: [PATCH] xcb: verify if xrandr present before using xcb_randr* APIs

Not doing so might break the connection. We have had similar
issues before, e.g. QTBUG-45312.

Change-Id: I95f15d24773fc92b052578bd72d1ba264d0a5f63
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
Reviewed-by: Uli Schlachter <psychon@znc.in>
---
 src/plugins/platforms/xcb/qxcbscreen.cpp | 35 ++++++++++++++++--------
 1 file changed, 23 insertions(+), 12 deletions(-)

diff --git a/src/plugins/platforms/xcb/qxcbscreen.cpp b/src/plugins/platforms/xcb/qxcbscreen.cpp
index ec0f9ba561..67c96b2d80 100644
--- a/src/plugins/platforms/xcb/qxcbscreen.cpp
+++ b/src/plugins/platforms/xcb/qxcbscreen.cpp
@@ -446,17 +446,24 @@ QXcbScreen::QXcbScreen(QXcbConnection *connection, QXcbVirtualDesktop *virtualDe
 
     m_cursor = new QXcbCursor(connection, this);
 
-    // Parse EDID
-    if (m_edid.parse(getEdid()))
-        qCDebug(lcQpaScreen, "EDID data for output \"%s\": identifier '%s', manufacturer '%s', model '%s', serial '%s', physical size: %.2fx%.2f",
-                name().toLatin1().constData(),
-                m_edid.identifier.toLatin1().constData(),
-                m_edid.manufacturer.toLatin1().constData(),
-                m_edid.model.toLatin1().constData(),
-                m_edid.serialNumber.toLatin1().constData(),
-                m_edid.physicalSize.width(), m_edid.physicalSize.height());
-    else
-        qCDebug(lcQpaScreen) << "Failed to parse EDID data for output" << name(); // keep this debug, not warning
+    if (connection->hasXRandr()) { // Parse EDID
+        QByteArray edid = getEdid();
+        if (m_edid.parse(edid)) {
+            qCDebug(lcQpaScreen, "EDID data for output \"%s\": identifier '%s', manufacturer '%s',"
+                                 "model '%s', serial '%s', physical size: %.2fx%.2f",
+                    name().toLatin1().constData(),
+                    m_edid.identifier.toLatin1().constData(),
+                    m_edid.manufacturer.toLatin1().constData(),
+                    m_edid.model.toLatin1().constData(),
+                    m_edid.serialNumber.toLatin1().constData(),
+                    m_edid.physicalSize.width(), m_edid.physicalSize.height());
+        } else {
+            // This property is defined by the xrandr spec. Parsing failure indicates a valid error,
+            // but keep this as debug, for details see 4f515815efc318ddc909a0399b71b8a684962f38.
+            qCDebug(lcQpaScreen) << "Failed to parse EDID data for output" << name() <<
+                                    "edid data: " << edid;
+        }
+    }
 }
 
 QXcbScreen::~QXcbScreen()
@@ -899,9 +906,13 @@ QByteArray QXcbScreen::getOutputProperty(xcb_atom_t atom) const
 
 QByteArray QXcbScreen::getEdid() const
 {
+    QByteArray result;
+    if (!connection()->hasXRandr())
+        return result;
+
     // Try a bunch of atoms
     xcb_atom_t atom = connection()->internAtom("EDID");
-    QByteArray result = getOutputProperty(atom);
+    result = getOutputProperty(atom);
     if (result.isEmpty()) {
         atom = connection()->internAtom("EDID_DATA");
         result = getOutputProperty(atom);