dm: core: Handle global_data moving in SPL

When CONFIG_SPL_STACK_R is enabled, and spl_init() is called before
board_init_r(), spl_relocate_stack_gd() will move global_data to a new
place in memory. This affects driver model since it uses a list for the
uclasses. Unless this is updated the list will become invalid. When
looking for a non-existent uclass, such as when adding a new one, the loop
in uclass_find() may continue forever, thus causing a hang.

Add a function to correct this rather obscure bug.

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

drivers/core/root.c

@@ -41,6 +41,13 @@ struct udevice *dm_root(void)
 	return gd->dm_root;
 }
 
+void dm_fixup_for_gd_move(struct global_data *new_gd)
+{
+	/* The sentinel node has moved, so update things that point to it */
+	new_gd->uclass_root.next->prev = &new_gd->uclass_root;
+	new_gd->uclass_root.prev->next = &new_gd->uclass_root;
+}
+
 fdt_addr_t dm_get_translation_offset(void)
 {
 	struct udevice *root = dm_root();