xcb: update libXi version requirement in the README file

... from 1.7.4 to 1.7.5 (released Sep, 2015).

Some more locking issues were fixed after 1.7.4. Testing
for a prolonged period of time has showed that 1.7.5 does
not cause a system lock-up.

[ChangeLog][Platform Specific Changes][X11 / XCB] Minimal libXi
version requirement has been updated from 1.7.4 to 1.7.5. This
is because XIAllowTouchEvents is known to deadlock with libXi 1.7.4
and earlier. When touch events are never received, this is not
an issue. Plain mouse / keyboard systems are not affected.

Task-number: QTBUG-62224
Change-Id: Ie70264b9af0390df33c417f660350d4bce48c6d3
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

1 files changed, 3 insertions, 2 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp b/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
index 26a9ba8d26..d1d97affe8 100644
--- a/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
@@ -700,8 +700,9 @@ void QXcbConnection::xi2ProcessTouch(void *xiDevEvent, QXcbWindow *platformWindo
         // Touches must be accepted when we are grabbing touch events. Otherwise the entire sequence
         // will get replayed when the grab ends.
         if (m_xiGrab) {
-            // XIAllowTouchEvents deadlocks with libXi < 1.7.4 (this has nothing to do with the XI2 versions like 2.2)
-            // http://lists.x.org/archives/xorg-devel/2014-July/043059.html
+            // Note that XIAllowTouchEvents is known to deadlock with older libXi versions,
+            // for details see qtbase/src/plugins/platforms/xcb/README. This has nothing to
+            // do with the XInput protocol version, but is a bug in libXi implementation instead.
             XIAllowTouchEvents(static_cast<Display *>(m_xlib_display), xiDeviceEvent->deviceid,
                                xiDeviceEvent->detail, xiDeviceEvent->event, XIAcceptTouch);
         }