Comment # 9 on bug 42960 from Sandeep

I booted Linux 3.13.6 with the drm.debug=4 parameter - it looks like the
internal LVDS output is set to use a different CRTC than the HDMI output, even
in clone mode.

The LVDS monitor's backlight is also off, it does not switch on at all or get
enabled after suspend and resume. Only a full system restart will bring it back
to life.