Created attachment 142919 [details]
Xorg.log with intel+nouveau drivers

I'm getting black output on HDMI-connected display driven by nVidia GeForce GT
525M (GF108M). Mouse cursor is visible on both built-in display and on the
external HDMI-connected display. This used to work on Fedora 27. I can see this
on Fedora 29, but I can't pinpoint which package update broke it because I
haven't checked the external display (a projector) for quite some time. This
machine is a Dell XPS 15 L502X with Intel HD3000 integrated graphics and nVidia
GeForce GT 525M discrete GPU in Optimus configuration. Here's my xorg.conf
snippet:

Section "Monitor"
        Identifier "Internal LCD"
        DisplaySize 345 195
EndSection

Section "Monitor"
        VendorName "Benq"
        ModelName  "W1100"
        Identifier "Projector"
        DisplaySize 16900 9400
EndSection

Section "Device"
        Identifier "Internal Graphics"
        Driver     "intel"
        Option     "Monitor-LVDS1" "Internal LCD"
        Option     "TearFree" "on"
EndSection

Section "Device"
        Identifier "Optimus Graphics"
        Driver     "nouveau"
        Option     "Monitor-HDMI-1-2" "Projector"
EndSection

Switching both drivers to "modesetting" makes the issue go away. I'm attaching
Xorg logs for both configurations.