fdt: Pass the device serial number through devicetree

Before device-tree, the device serial number used to be passed to the kernel
using ATAGs (on ARM). This is now deprecated and all the handover to the kernel
should now be done using device-tree. Thus, this passes the serial-number
property to the kernel using the serial-number property of the root node, as
expected by the kernel.

The serial number is a string that somewhat represents the device's serial
number. It might come from some form of storage (e.g. an eeprom) and be
programmed at factory-time by the manufacturer or come from identification
bits available in e.g. the SoC.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Reviewed-by: Simon Glass <sgj@chromium.org>

common/fdt_support.c

@@ -194,6 +194,31 @@ static inline int fdt_setprop_uxx(void *fdt, int nodeoffset, const char *name,
 		return fdt_setprop_u32(fdt, nodeoffset, name, (uint32_t)val);
 }
 
+int fdt_root(void *fdt)
+{
+	char *serial;
+	int err;
+
+	err = fdt_check_header(fdt);
+	if (err < 0) {
+		printf("fdt_root: %s\n", fdt_strerror(err));
+		return err;
+	}
+
+	serial = getenv("serial#");
+	if (serial) {
+		err = fdt_setprop(fdt, 0, "serial-number", serial,
+				  strlen(serial) + 1);
+
+		if (err < 0) {
+			printf("WARNING: could not set serial-number %s.\n",
+			       fdt_strerror(err));
+			return err;
+		}
+	}
+
+	return 0;
+}
 
 int fdt_initrd(void *fdt, ulong initrd_start, ulong initrd_end)
 {

common/image-fdt.c

@@ -471,6 +471,10 @@ int image_setup_libfdt(bootm_headers_t *images, void *blob,
 	int ret = -EPERM;
 	int fdt_ret;
 
+	if (fdt_root(blob) < 0) {
+		printf("ERROR: root node setup failed\n");
+		goto err;
+	}
 	if (fdt_chosen(blob) < 0) {
 		printf("ERROR: /chosen node create failed\n");
 		goto err;

doc/device-tree-bindings/root.txt

@@ -0,0 +1,4 @@
+The root node
+
+Optional properties:
+  - serial-number : a string representing the device's serial number

include/fdt_support.h

@@ -16,6 +16,7 @@ u32 fdt_getprop_u32_default_node(const void *fdt, int off, int cell,
 				const char *prop, const u32 dflt);
 u32 fdt_getprop_u32_default(const void *fdt, const char *path,
 				const char *prop, const u32 dflt);
+int fdt_root(void *fdt);
 int fdt_chosen(void *fdt);
 int fdt_initrd(void *fdt, ulong initrd_start, ulong initrd_end);
 void do_fixup_by_path(void *fdt, const char *path, const char *prop,