I just installed Arch on a ThinkPad P50 and and hacking my way through DE's looking for something that works with HiDpi. So far KDE is looking the most promising but I have a weird issue. Whenever I plug a second screen in, my laptop screen starts flickering, as it normally would 1-2 times as it's figuring out it's setting for the new scree, but it does it forever. The secondary screen wakes up and then falls asleep indefinitely, never shows an image. However, if I boot with the screen plugged in, the second screen works just fine, though it's on the wrong side, and not scaled properly. If I change any settings it goes into strobe mode like before.

Laptop screen is 4k
Second screen is 2k
Nvidia Quadro GPU set to always on (no intel hybrid graphics)
Using 'nvidia' driver, which works with Unity on Ubuntu decently well

If I unplug the second monitor it goes back to working and says that KWin crashed. Here's the crash log:

Code: Select all

Application: KWin (kwin_x11), signal: Segmentation fault
Using host libthread_db library "/usr/lib/libthread_db.so.1".
[Current thread is 1 (Thread 0x7fa29896c840 (LWP 1843))]

Thread 5 (Thread 0x7fa256f53700 (LWP 1863)):
#0  0x00007fa2915e410f in pthread_cond_wait@@GLIBC_2.3.2 () at /usr/lib/libpthread.so.0
#1  0x00007fa29495b234 in  () at /usr/lib/libQt5Script.so.5
#2  0x00007fa29495b279 in  () at /usr/lib/libQt5Script.so.5
#3  0x00007fa2915de454 in start_thread () at /usr/lib/libpthread.so.0
#4  0x00007fa2983a07df in clone () at /usr/lib/libc.so.6

Thread 4 (Thread 0x7fa269a08700 (LWP 1861)):
#0  0x00007fa2915e44b8 in pthread_cond_timedwait@@GLIBC_2.3.2 () at /usr/lib/libpthread.so.0
#1  0x00007fa2742fee44 in  () at /usr/lib/libGLX_nvidia.so.0
#2  0x00007fa26a7d4394 in  () at /usr/lib/libnvidia-glcore.so.378.13
#3  0x00007fa2742fe12c in  () at /usr/lib/libGLX_nvidia.so.0
#4  0x00007fa2915de454 in start_thread () at /usr/lib/libpthread.so.0
#5  0x00007fa2983a07df in clone () at /usr/lib/libc.so.6

Thread 3 (Thread 0x7fa27558c700 (LWP 1857)):
#0  0x00007fa298397551 in ppoll () at /usr/lib/libc.so.6
#1  0x00007fa295a1c2f9 in qt_safe_poll(pollfd*, unsigned long, timespec const*) () at /usr/lib/libQt5Core.so.5
#2  0x00007fa295a1d96a in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#3  0x00007fa2959ca89a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#4  0x00007fa2957eca73 in QThread::exec() () at /usr/lib/libQt5Core.so.5
#5  0x00007fa2902ed025 in  () at /usr/lib/libQt5Qml.so.5
#6  0x00007fa2957f16d8 in  () at /usr/lib/libQt5Core.so.5
#7  0x00007fa2915de454 in start_thread () at /usr/lib/libpthread.so.0
#8  0x00007fa2983a07df in clone () at /usr/lib/libc.so.6

Thread 2 (Thread 0x7fa27cf8d700 (LWP 1850)):
#0  0x00007fa298397551 in ppoll () at /usr/lib/libc.so.6
#1  0x00007fa295a1c2f9 in qt_safe_poll(pollfd*, unsigned long, timespec const*) () at /usr/lib/libQt5Core.so.5
#2  0x00007fa295a1d96a in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#3  0x00007fa2959ca89a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#4  0x00007fa2957eca73 in QThread::exec() () at /usr/lib/libQt5Core.so.5
#5  0x00007fa28f4a3125 in  () at /usr/lib/libQt5DBus.so.5
#6  0x00007fa2957f16d8 in  () at /usr/lib/libQt5Core.so.5
#7  0x00007fa2915de454 in start_thread () at /usr/lib/libpthread.so.0
#8  0x00007fa2983a07df in clone () at /usr/lib/libc.so.6

Thread 1 (Thread 0x7fa29896c840 (LWP 1843)):
[KCrash Handler]
#6  0x00007fa29519a204 in KWin::WindowQuadList::makeInterleavedArrays(unsigned int, KWin::GLVertex2D*, QMatrix4x4 const&) const () at /usr/lib/libkwineffects.so.10
#7  0x00007fa297f3903b in  () at /usr/lib/libkwin.so.5
#8  0x00007fa297f376e2 in  () at /usr/lib/libkwin.so.5
#9  0x00007fa297f377c4 in  () at /usr/lib/libkwin.so.5
#10 0x00007fa297f4cbe9 in KWin::EffectsHandlerImpl::drawWindow(KWin::EffectWindow*, int, QRegion, KWin::WindowPaintData&) () at /usr/lib/libkwin.so.5
#11 0x00007fa294d2d0e8 in  () at /usr/lib/libkwin4_effect_builtins.so.1
#12 0x00007fa297f4cb7e in KWin::EffectsHandlerImpl::drawWindow(KWin::EffectWindow*, int, QRegion, KWin::WindowPaintData&) () at /usr/lib/libkwin.so.5
#13 0x00007fa294c945f7 in  () at /usr/lib/libkwin4_effect_builtins.so.1
#14 0x00007fa297f4cb7e in KWin::EffectsHandlerImpl::drawWindow(KWin::EffectWindow*, int, QRegion, KWin::WindowPaintData&) () at /usr/lib/libkwin.so.5
#15 0x00007fa297f16571 in KWin::Scene::finalPaintWindow(KWin::EffectWindowImpl*, int, QRegion, KWin::WindowPaintData&) () at /usr/lib/libkwin.so.5
#16 0x00007fa297f4ca2a in KWin::EffectsHandlerImpl::paintWindow(KWin::EffectWindow*, int, QRegion, KWin::WindowPaintData&) () at /usr/lib/libkwin.so.5
#17 0x00007fa295195731 in KWin::Effect::paintWindow(KWin::EffectWindow*, int, QRegion, KWin::WindowPaintData&) () at /usr/lib/libkwineffects.so.10
#18 0x00007fa297f4c9ce in KWin::EffectsHandlerImpl::paintWindow(KWin::EffectWindow*, int, QRegion, KWin::WindowPaintData&) () at /usr/lib/libkwin.so.5
#19 0x00007fa295195731 in KWin::Effect::paintWindow(KWin::EffectWindow*, int, QRegion, KWin::WindowPaintData&) () at /usr/lib/libkwineffects.so.10
#20 0x00007fa297f4c9ce in KWin::EffectsHandlerImpl::paintWindow(KWin::EffectWindow*, int, QRegion, KWin::WindowPaintData&) () at /usr/lib/libkwin.so.5
#21 0x00007fa297f1de09 in KWin::Scene::paintWindow(KWin::Scene::Window*, int, QRegion, KWin::WindowQuadList) () at /usr/lib/libkwin.so.5
#22 0x00007fa297f1a7ab in KWin::Scene::paintSimpleScreen(int, QRegion) () at /usr/lib/libkwin.so.5
#23 0x00007fa297f2eca0 in  () at /usr/lib/libkwin.so.5
#24 0x00007fa297f1d214 in KWin::Scene::finalPaintScreen(int, QRegion, KWin::ScreenPaintData&) () at /usr/lib/libkwin.so.5
#25 0x00007fa297f4c7af in KWin::EffectsHandlerImpl::paintScreen(int, QRegion, KWin::ScreenPaintData&) () at /usr/lib/libkwin.so.5
#26 0x00007fa29519567f in KWin::Effect::paintScreen(int, QRegion, KWin::ScreenPaintData&) () at /usr/lib/libkwineffects.so.10
#27 0x00007fa297f4c75a in KWin::EffectsHandlerImpl::paintScreen(int, QRegion, KWin::ScreenPaintData&) () at /usr/lib/libkwin.so.5
#28 0x00007fa29519567f in KWin::Effect::paintScreen(int, QRegion, KWin::ScreenPaintData&) () at /usr/lib/libkwineffects.so.10
#29 0x00007fa297f4c75a in KWin::EffectsHandlerImpl::paintScreen(int, QRegion, KWin::ScreenPaintData&) () at /usr/lib/libkwin.so.5
#30 0x00007fa297f1cea2 in KWin::Scene::paintScreen(int*, QRegion const&, QRegion const&, QRegion*, QRegion*, QMatrix4x4 const&, QRect const&) () at /usr/lib/libkwin.so.5
#31 0x00007fa297f33349 in KWin::SceneOpenGL::paint(QRegion, QList<KWin::Toplevel*>) () at /usr/lib/libkwin.so.5
#32 0x00007fa297f0d511 in KWin::Compositor::performCompositing() () at /usr/lib/libkwin.so.5
#33 0x00007fa2959f8b63 in QObject::event(QEvent*) () at /usr/lib/libQt5Core.so.5
#34 0x00007fa2966ae34c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /usr/lib/libQt5Widgets.so.5
#35 0x00007fa2966b5b61 in QApplication::notify(QObject*, QEvent*) () at /usr/lib/libQt5Widgets.so.5
#36 0x00007fa2959cc440 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /usr/lib/libQt5Core.so.5
#37 0x00007fa295a1fcbe in QTimerInfoList::activateTimers() () at /usr/lib/libQt5Core.so.5
#38 0x00007fa295a1dbda in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#39 0x00007fa280219ded in  () at /usr/lib/libQt5XcbQpa.so.5
#40 0x00007fa2959ca89a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#41 0x00007fa2959d2de4 in QCoreApplication::exec() () at /usr/lib/libQt5Core.so.5
#42 0x00007fa29865f391 in kdemain () at /usr/lib/libkdeinit5_kwin_x11.so
#43 0x00007fa2982d8291 in __libc_start_main () at /usr/lib/libc.so.6
#44 0x000000000040069a in _start ()

I fixed it myself by switching from nvidia to nouveau as per the arch wiki.