Comment 30 for bug 1104230

VIncent, according to [1] this hardware is displayport 1.2 compatible.
"Plus, the Display Port 1.2 adds the ability to daisy chain displays (4 displays via 1 connector)."

However, I have not been able to determine whether this works in such a way that it takes MST output from your laptop's displayport and distributes it via vga and dvi ports.

Do you remember what feature have you been cherry picking to your patched kernel? Maybe you were using another feature.

The perfect setup to test this feature is the one Elvishas - daisy chained Dell monitors.

Regarding your question on the xorg-edgers driver: can you please try
sudo add-apt-repository -y ppa:xorg-edgers/ppa
sudo apt-get update
apt-cache policy xserver-xorg-video-intel

Please provide the output of the last command. Thanks.

[1] http://accessories.us.dell.com/sna/productdetail.aspx?c=us&l=en&s=gen&sku=331-6307