dm: Cast away the const-ness of the global_data pointer

In a very few cases we need to adjust the driver model root device, such as
when setting it up at initialisation. Add a macro to make this easier.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/core/root.c

@@ -43,9 +43,9 @@ int dm_init(void)
 		dm_warn("Virtual root driver already exists!\n");
 		return -EINVAL;
 	}
-	INIT_LIST_HEAD(&gd->uclass_root);
+	INIT_LIST_HEAD(&DM_UCLASS_ROOT_NON_CONST);
 
-	ret = device_bind_by_name(NULL, &root_info, &gd->dm_root);
+	ret = device_bind_by_name(NULL, &root_info, &DM_ROOT_NON_CONST);
 	if (ret)
 		return ret;
 
@@ -56,7 +56,7 @@ int dm_scan_platdata(void)
 {
 	int ret;
 
-	ret = lists_bind_drivers(gd->dm_root);
+	ret = lists_bind_drivers(DM_ROOT_NON_CONST);
 	if (ret == -ENOENT) {
 		dm_warn("Some drivers were not found\n");
 		ret = 0;

drivers/core/uclass.c

@@ -75,7 +75,7 @@ static int uclass_add(enum uclass_id id, struct uclass **ucp)
 	uc->uc_drv = uc_drv;
 	INIT_LIST_HEAD(&uc->sibling_node);
 	INIT_LIST_HEAD(&uc->dev_head);
-	list_add(&uc->sibling_node, &gd->uclass_root);
+	list_add(&uc->sibling_node, &DM_UCLASS_ROOT_NON_CONST);
 
 	if (uc_drv->init) {
 		ret = uc_drv->init(uc);

include/dm/device-internal.h

@@ -84,4 +84,8 @@ int device_remove(struct udevice *dev);
  */
 int device_unbind(struct udevice *dev);
 
+/* Cast away any volatile pointer */
+#define DM_ROOT_NON_CONST		(((gd_t *)gd)->dm_root)
+#define DM_UCLASS_ROOT_NON_CONST	(((gd_t *)gd)->uclass_root)
+
 #endif