drm/i915: Extract checking for backing struct pages to a helper

Currently to see if an object is backed by struct pages (as opposed to
being a simple pointer to stolen memory, for example) we do a manual
check on the obj->ops->flags. This is quite shouty and before adding
more checks in future, we should make it a bit calmer.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1466431552-17860-1-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.h

@@ -2266,6 +2266,12 @@ struct drm_i915_gem_object {
 };
 #define to_intel_bo(x) container_of(x, struct drm_i915_gem_object, base)
 
+static inline bool
+i915_gem_object_has_struct_page(const struct drm_i915_gem_object *obj)
+{
+	return obj->ops->flags & I915_GEM_OBJECT_HAS_STRUCT_PAGE;
+}
+
 /*
  * Optimised SGL iterator for GEM objects
  */

drivers/gpu/drm/i915/i915_gem.c

@@ -508,7 +508,7 @@ int i915_gem_obj_prepare_shmem_read(struct drm_i915_gem_object *obj,
 
 	*needs_clflush = 0;
 
-	if (WARN_ON((obj->ops->flags & I915_GEM_OBJECT_HAS_STRUCT_PAGE) == 0))
+	if (WARN_ON(!i915_gem_object_has_struct_page(obj)))
 		return -EINVAL;
 
 	if (!(obj->base.read_domains & I915_GEM_DOMAIN_CPU)) {
@@ -5528,7 +5528,7 @@ i915_gem_object_get_dirty_page(struct drm_i915_gem_object *obj, int n)
 	struct page *page;
 
 	/* Only default objects have per-page dirty tracking */
-	if (WARN_ON((obj->ops->flags & I915_GEM_OBJECT_HAS_STRUCT_PAGE) == 0))
+	if (WARN_ON(!i915_gem_object_has_struct_page(obj)))
 		return NULL;
 
 	page = i915_gem_object_get_page(obj, n);