Bug#897618: linux-image-4.17.0-rc3-amd64-unsigned: xrandr gives a black screen for some resolutions

[Reinhard Karcher <reinhard.karcher@gmx.net>]

Package: src:linux
Version: 4.17~rc3-1~exp1
Severity: normal

My laptop has a resolution of 1920x1080.
xrandr -s 800x600 results in a black screen.
Using KDE, I can leave the session by typing ctrl-alt-delete
while the screen is black.
A resolution of 1360x768 is working.
/sys/kernel/debug/dri/0/framebuffer contains:
framebuffer[82]:
        allocated by = Xorg
        refcount=1
        format=XR24 little-endian (0x34325258)
        modifier=0x100000000000001
        size=800x600
        layers:
                size[0]=800x600
                pitch[0]=3584
                offset[0]=0
                obj[0]:(null)