drm/i915: clear the stolen fb before resuming

Similar to
commit 88afe715dd5469bc24ca7a19ac62dd3c241cab48
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Sun Dec 16 12:15:41 2012 +0000

    drm/i915: Clear the stolen fb before enabling

but on the resume path.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=57191
Reported-and-tested-by: Nikolay Amiantov <nikoamia@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@vger.kernel.org (3.9 only)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_fb.c

@@ -262,10 +262,22 @@ void intel_fbdev_fini(struct drm_device *dev)
 void intel_fbdev_set_suspend(struct drm_device *dev, int state)
 {
 	drm_i915_private_t *dev_priv = dev->dev_private;
-	if (!dev_priv->fbdev)
+	struct intel_fbdev *ifbdev = dev_priv->fbdev;
+	struct fb_info *info;
+
+	if (!ifbdev)
 		return;
 
-	fb_set_suspend(dev_priv->fbdev->helper.fbdev, state);
+	info = ifbdev->helper.fbdev;
+
+	/* On resume from hibernation: If the object is shmemfs backed, it has
+	 * been restored from swap. If the object is stolen however, it will be
+	 * full of whatever garbage was left in there.
+	 */
+	if (!state && ifbdev->ifb.obj->stolen)
+		memset_io(info->screen_base, 0, info->screen_size);
+
+	fb_set_suspend(info, state);
 }
 
 MODULE_LICENSE("GPL and additional rights");