Intel i915 GPU hung

Hello,

I have just upgrade my laptop, a Samsung Ativ Book 2 with an integrated
Intel HD Graphics 4000, to:

FreeBSD ativ.local 11.0-CURRENT FreeBSD 11.0-CURRENT #0 r271400: Wed Sep 10
21:40:48 CEST 2014     root_at_ativ.local:/usr/obj/usr/src/sys/NEWCONS  amd64

Using Firefox, after some minutes, I receive the error:

error: [drm:pid12:i915_hangcheck_elapsed] *ERROR* Hangcheck timer
elapsed... GPU hung
info: [drm] capturing error event; look for more information in sysctl
hw.dri.0.info.i915_error_state

This error is not related to r271400, but I first saw it few months ago in
current.

The output of the command
sysctl hw.dri.0.info.i915_error_state
is:

https://drive.google.com/file/d/0BzoWQoMqq1sfa0tyVGJVYVBhRnc/edit?usp=sharing

After the error I am not able to run mplayer for videos: the window is
black.

Regards,
Maurizio