um: Unconditionally call unflatten_device_tree()

Call this function unconditionally so that we can populate an empty DTB
on platforms that don't boot with a command line provided DTB.  There's
no harm in calling unflatten_device_tree() unconditionally. If there
isn't a valid initial_boot_params dtb then unflatten_device_tree()
returns early.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <frowand.list@gmail.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: linux-um@lists.infradead.org
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lore.kernel.org/r/20240217010557.2381548-4-sboyd@kernel.orgSigned-off-by: Rob Herring <robh@kernel.org>

arch/um/kernel/dtb.c

@@ -16,16 +16,16 @@ void uml_dtb_init(void)
 	void *area;
 
 	area = uml_load_file(dtb, &size);
-	if (!area)
-		return;
-
-	if (!early_init_dt_scan(area)) {
-		pr_err("invalid DTB %s\n", dtb);
-		memblock_free(area, size);
-		return;
+	if (area) {
+		if (!early_init_dt_scan(area)) {
+			pr_err("invalid DTB %s\n", dtb);
+			memblock_free(area, size);
+			return;
+		}
+
+		early_init_fdt_scan_reserved_mem();
 	}
 
-	early_init_fdt_scan_reserved_mem();
 	unflatten_device_tree();
 }
 

drivers/of/unittest.c

@@ -4087,10 +4087,6 @@ static int __init of_unittest(void)
 	add_taint(TAINT_TEST, LOCKDEP_STILL_OK);
 
 	/* adding data for unittest */
-
-	if (IS_ENABLED(CONFIG_UML))
-		unittest_unflatten_overlay_base();
-
 	res = unittest_data_add();
 	if (res)
 		return res;