drm/i915: Restore fences after resume and GPU resets

Stéphane Marchesin found that fences for pinned objects (i.e. the
scanout) were not being restored upon resume, leading to corruption on
the display and reference counting issues. This is due to a bug in

commit 312817a39f [2.6.38]
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Mon Nov 22 11:50:11 2010 +0000

    drm/i915: Only save and restore fences for UMS

that zapped the pinned fences even though they were in use.
Fortuitously, whilst we forced a VT switch during suspend and resume,
no fences were ever pinned at the time. However, we now can do
switchless S3 transitions and so the old bug finally surfaces.

Reported-by: Stéphane Marchesin <marcheu@chromium.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Stéphane Marchesin <marcheu@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_suspend.c

@@ -384,6 +384,7 @@ int i915_restore_state(struct drm_device *dev)
 
 	mutex_lock(&dev->struct_mutex);
 
+	i915_gem_restore_fences(dev);
 	i915_restore_display(dev);
 
 	if (!drm_core_check_feature(dev, DRIVER_MODESET)) {