[PATCH V2 XRT Alveo Infrastructure 4/9] of: create empty of root

[Lizhi Hou <lizhi.hou@xxxxxxxxxx>]

When OF_FLATTREE is selected and there is not a device tree, create an
empty device tree root node. of/unittest.c code is referenced.

Signed-off-by: Sonal Santan <sonal.santan@xxxxxxxxxx>
Signed-off-by: Max Zhen <max.zhen@xxxxxxxxxx>
Signed-off-by: Lizhi Hou <lizhi.hou@xxxxxxxxxx>
---
 drivers/of/Makefile        |  2 +-
 drivers/of/fdt.c           | 20 ++++++++++++++++++++
 drivers/of/fdt_default.dts |  5 +++++
 drivers/of/of_private.h    |  5 +++++
 4 files changed, 31 insertions(+), 1 deletion(-)
 create mode 100644 drivers/of/fdt_default.dts

diff --git a/drivers/of/Makefile b/drivers/of/Makefile
index c13b982084a3..815f5220465b 100644
--- a/drivers/of/Makefile
+++ b/drivers/of/Makefile
@@ -2,7 +2,7 @@
 obj-y = base.o device.o platform.o property.o
 obj-$(CONFIG_OF_KOBJ) += kobj.o
 obj-$(CONFIG_OF_DYNAMIC) += dynamic.o
-obj-$(CONFIG_OF_FLATTREE) += fdt.o
+obj-$(CONFIG_OF_FLATTREE) += fdt.o fdt_default.dtb.o
 obj-$(CONFIG_OF_EARLY_FLATTREE) += fdt_address.o
 obj-$(CONFIG_OF_PROMTREE) += pdt.o
 obj-$(CONFIG_OF_ADDRESS)  += address.o
diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index d64445e43ceb..3d6e4543419e 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -481,6 +481,26 @@ void *of_fdt_unflatten_tree(const unsigned long *blob,
 }
 EXPORT_SYMBOL_GPL(of_fdt_unflatten_tree);
 
+static int __init of_fdt_root_init(void)
+{
+	struct device_node *np;
+
+	if (of_root)
+		return 0;
+
+	if (!of_fdt_unflatten_tree((const unsigned long *)__dtb_fdt_default_begin,
+				   NULL, &of_root)) {
+		pr_warn("%s: unflatten default tree failed\n", __func__);
+		return -ENODATA;
+	}
+
+	for_each_of_allnodes(np)
+		__of_attach_node_sysfs(np);
+
+	return 0;
+}
+late_initcall(of_fdt_root_init);
+
 /* Everything below here references initial_boot_params directly. */
 int __initdata dt_root_addr_cells;
 int __initdata dt_root_size_cells;
diff --git a/drivers/of/fdt_default.dts b/drivers/of/fdt_default.dts
new file mode 100644
index 000000000000..d1f12a76dfc6
--- /dev/null
+++ b/drivers/of/fdt_default.dts
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0
+/dts-v1/;
+
+/ {
+};
diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index 631489f7f8c0..47c6bb47ef25 100644
--- a/drivers/of/of_private.h
+++ b/drivers/of/of_private.h
@@ -41,6 +41,11 @@ extern struct mutex of_mutex;
 extern struct list_head aliases_lookup;
 extern struct kset *of_kset;
 
+#if defined(CONFIG_OF_FLATTREE)
+extern u8 __dtb_fdt_default_begin[];
+extern u8 __dtb_fdt_default_end[];
+#endif
+
 #if defined(CONFIG_OF_DYNAMIC)
 extern int of_property_notify(int action, struct device_node *np,
 			      struct property *prop, struct property *old_prop);
-- 
2.27.0