drm/i915: Disable pwrctx before unpin and free

Otherwise the chip may scribble over free memory.
Signed-off-by: NKristian Høgsberg <krh@bitplanet.net>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NEric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/intel_display.c

@@ -4588,6 +4588,11 @@ void intel_modeset_cleanup(struct drm_device *dev)
 		dev_priv->display.disable_fbc(dev);
 
 	if (dev_priv->pwrctx) {
+		struct drm_i915_gem_object *obj_priv;
+
+		obj_priv = dev_priv->pwrctx->driver_private;
+		I915_WRITE(PWRCTXA, obj_priv->gtt_offset &~ PWRCTX_EN);
+		I915_READ(PWRCTXA);
 		i915_gem_object_unpin(dev_priv->pwrctx);
 		drm_gem_object_unreference(dev_priv->pwrctx);
 	}