drm/i915: unpin pages at unbind

If we properly keep track of the pages_pin_count, then when we later add
multiple address spaces, the put_pages doesn't need any special checks
to be able to perform it's job.

CC: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
[danvet: Rebased on top of the fix for stolen memory pinning.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -2511,6 +2511,7 @@ i915_gem_object_unbind(struct drm_i915_gem_object *obj)
 		obj->has_aliasing_ppgtt_mapping = 0;
 	}
 	i915_gem_gtt_finish_object(obj);
+	i915_gem_object_unpin_pages(obj);
 
 	list_del(&obj->mm_list);
 	list_move_tail(&obj->gtt_list, &dev_priv->mm.unbound_list);
@@ -3060,7 +3061,6 @@ i915_gem_object_bind_to_gtt(struct drm_i915_gem_object *obj,
 
 	obj->map_and_fenceable = mappable && fenceable;
 
-	i915_gem_object_unpin_pages(obj);
 	trace_i915_gem_object_bind(obj, map_and_fenceable);
 	i915_gem_verify_gtt(dev);
 	return 0;
@@ -3865,6 +3865,7 @@ void i915_gem_free_object(struct drm_gem_object *gem_obj)
 	if (obj->stolen)
 		i915_gem_object_unpin_pages(obj);
 
+	if (WARN_ON(obj->pages_pin_count))
 		obj->pages_pin_count = 0;
 	i915_gem_object_put_pages(obj);
 	i915_gem_object_free_mmap_offset(obj);