Created attachment 101308 [details]
dmesg with drm.debug=0x06

commit e2bfa715a9e115921263d572b9f4c496b550a494
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Tue Jun 10 21:28:32 2014 +0100

    sna/dri2: Check that the window covers the whole CRTC before xchg
    
    Fixes TearFre regression from
    
    commit 3932e97057fca16615adaefbc1eb25a0d51a1d8b [2.99.912]
    Author: Chris Wilson <chris@chris-wilson.co.uk>
    Date:   Mon Jun 9 08:58:15 2014 +0100
    
        sna/dri2: Allow TearFree flipping to individual CRTC
    
    Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

Hmm, this happens on current git. Also the window does cover the whole crtc. 

This consistently fails: Start glxgears, move it to the second monitor, put it in fullscreen, put it out of fullscreen. Screen switches off.

Created attachment 101312 [details]
hopefully part of Xorg.0.log with full debug output

Ah, jumped to a conclusion as the kernel log seemed familiar.

This should fix it:

commit 83c0f034454ef0f474126a3398e5e790ac5ef842
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Wed Jun 18 16:51:46 2014 +0100

    sna: Pass desired CRTC viewport for completing single CRTC flips
    
    We cannot simply compare against the crtc->shadow_bo for all our needs,
    so pass in exactly the setup we want and apply that. In particular this
    is required when flipping away from the single CRTC setup on secondary
    pipes.
    
    Fixes TearFree multi-monitor regression from
    commit 3932e97057fca16615adaefbc1eb25a0d51a1d8b [2.99.912]
    Author: Chris Wilson <chris@chris-wilson.co.uk>
    Date:   Mon Jun 9 08:58:15 2014 +0100
    
        sna/dri2: Allow TearFree flipping to individual CRTC
    
    Reported-by: Leo Wolf <jclw@ymail.com>
    Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=80191

Yes, that works. Thank you!