Comment 147 for bug 1275794

(In reply to comment #125)
> (In reply to comment #115)
> > I tried applying the two patches which you posted on intel-gfx[1], ported to
> > 3.13.
> >
> > [1] http://article.gmane.org/gmane.comp.freedesktop.xorg.drivers.intel/33737
> >
> > Using a T540p and an Ultradock, connected to a Dell U2410 via a DisplayPort
> > cable --- and it worked! Not only were there no hangs, but in fact I could
> > enable and disable the external display. The "too many retries" did indeed
> > trigger:
>
> These patches did not work for me with my T440s. During bootup it hangs
> upon switch to FB. Once booted undocked, it hangs when docked and external
> monitor is enabled through xrandr.

Try to update your dock to the new firmware. It should resolve this issue, at least if you are using only a single external display!