Re: Problems w/Sandy Bridge & 27" monitor

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Aug 15, 2012 at 06:38:10PM -0400, Chun-Yu Shei wrote:
> Hi,
> 
> I recently upgraded to a 27" monitor (2560x1440) from a 23" one
> (1920x1080), and had to switch to Windows because the new monitor is
> unusable in Linux.  Today, about a month later, I decided to give
> Linux another try, since there have been several updates to the
> Intel graphics driver since then.
> 
> Unfortunately, it seems that it's still unusable with
> xf86-video-intel 2.20.3 -- after a little while, the video signal to
> the 27" monitor completely stops, and it goes into power saving
> mode.  I'm running dual monitors with the old 23", and that one
> continues running fine when this happens.  This happens on my
> ThinkPad X220 (i5-2540M).  The 27" is connected via DisplayPort, and
> the 23" via DVI.  SNA is enabled, if it makes any difference (I
> haven't tried turning it off, but I probably should).  This is the
> biggest problem I'm facing when it comes to Linux support.
> 
> I also gave the new "TearFree" option a try, and while it does a
> great job of eliminating tearing, it makes the two monitors become
> mirrors of each other for some reason.  If I take a screenshot with
> the GNOME tool, the screenshot comes out as expected (unmirrored),
> but the video output on the two monitors is mirrored in reality.
> Disabling "TearFree" fixes this.
> 
> Also, when I'm using the ThinkPad's built-in display, it sometimes
> turns off for no apparent reason, although it's not too big of a
> deal since a suspend/resume cycle seems to fix things (and I haven't
> used 2.20.3 long enough to experience this yet).
> 
> Any ideas/things I can do to help track these issues down?

For the screen blanking issues, the kernel is the important part. Please
boot with drm.debug=0xe added to your kernel bootline and grab the full
dmesg.
-Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48