With my Radeon HD 7770 and the open radeonsi driver (on Kernel 3.11.x), I am unable to output to an HDTV using HDMI. Only DVI works. GNOME's display settings never "sees" the additional screen, and xrandr always thinks that the HDMI port is disconnected, like so: Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 16384 x 16384 DisplayPort-0 disconnected (normal left inverted right x axis y axis) DisplayPort-1 disconnected (normal left inverted right x axis y axis) HDMI-0 disconnected (normal left inverted right x axis y axis) DVI-0 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 598mm x 336mm 1920x1080 60.0*+ 1280x1024 60.0 1440x900 59.9 1280x800 59.9 1152x864 75.0 1024x768 70.1 60.0 800x600 60.3 56.2 640x480 66.7 60.0 720x400 70.1
Created attachment 812727 [details] Xorg log
Created attachment 812728 [details] dmesg
Created attachment 812729 [details] lspci -vvvv
Issue persists in F20.
Interestingly enough, this is not an issue if the HDMI cable was plugged in at poweron/boot time instead of hotplugged: when cold-plugged, both screens are turned on.
Turns out it was a physical PEBKAC with the connector.