drm/vram-helper: don't use ttm bo->offset v4

Calculate GEM VRAM bo's offset within vram-helper without depending on
bo->offset.
Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/372938/

drivers/gpu/drm/drm_gem_vram_helper.c

@@ -281,6 +281,15 @@ u64 drm_gem_vram_mmap_offset(struct drm_gem_vram_object *gbo)
 }
 EXPORT_SYMBOL(drm_gem_vram_mmap_offset);
 
+static u64 drm_gem_vram_pg_offset(struct drm_gem_vram_object *gbo)
+{
+	/* Keep TTM behavior for now, remove when drivers are audited */
+	if (WARN_ON_ONCE(!gbo->bo.mem.mm_node))
+		return 0;
+
+	return gbo->bo.mem.start;
+}
+
 /**
  * drm_gem_vram_offset() - \
 	Returns a GEM VRAM object's offset in video memory
@@ -297,7 +306,7 @@ s64 drm_gem_vram_offset(struct drm_gem_vram_object *gbo)
 {
 	if (WARN_ON_ONCE(!gbo->pin_count))
 		return (s64)-ENODEV;
-	return gbo->bo.offset;
+	return drm_gem_vram_pg_offset(gbo) << PAGE_SHIFT;
 }
 EXPORT_SYMBOL(drm_gem_vram_offset);