drm/i915: Extract tile_row_size for fencing

Computing the tile row size of a tiled object (for use with fence
registers) is repeated, so extract it to a common helper.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170109161613.11881-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index ed3cd1a..e8e278f 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1696,12 +1696,7 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
 
 static unsigned int tile_row_pages(struct drm_i915_gem_object *obj)
 {
-	u64 size;
-
-	size = i915_gem_object_get_stride(obj);
-	size *= i915_gem_object_get_tiling(obj) == I915_TILING_Y ? 32 : 8;
-
-	return size >> PAGE_SHIFT;
+	return i915_gem_object_get_tile_row_size(obj) >> PAGE_SHIFT;
 }
 
 /**