env: allow environment to be amended from control dtb

It can be useful to use the same U-Boot binary for multiple purposes,
say the normal one, one for developers that allow breaking into the
U-Boot shell, and one for use during bootstrapping which runs a
special-purpose bootcmd. Or one can have several board variants that
can share almost all boot logic, but just needs a few tweaks in the
variables used by the boot script.

To that end, allow the control dtb to contain a /config/enviroment
node (or whatever one puts in fdt_env_path variable), whose
property/value pairs are used to update the run-time environment after
it has been loaded from its persistent location.

The indirection via fdt_env_path is for maximum flexibility - for
example, should the user wish (or board logic dictate) that the values
in the DTB should no longer be applied, one simply needs to delete the
fdt_env_path variable; that can even be done automatically by
including a

  fdt_env_path = "";

property in the DTB node.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

env/common.c

@@ -20,6 +20,7 @@
 #include <errno.h>
 #include <malloc.h>
 #include <u-boot/crc.h>
+#include <dm/ofnode.h>
 
 DECLARE_GLOBAL_DATA_PTR;
 
@@ -334,3 +335,32 @@ int env_complete(char *var, int maxv, char *cmdv[], int bufsz, char *buf,
 	return found;
 }
 #endif
+
+#ifdef CONFIG_ENV_IMPORT_FDT
+void env_import_fdt(void)
+{
+	const char *path;
+	struct ofprop prop;
+	ofnode node;
+	int res;
+
+	path = env_get("env_fdt_path");
+	if (!path || !path[0])
+		return;
+
+	node = ofnode_path(path);
+	if (!ofnode_valid(node)) {
+		printf("Warning: device tree node '%s' not found\n", path);
+		return;
+	}
+
+	for (res = ofnode_get_first_property(node, &prop);
+	     !res;
+	     res = ofnode_get_next_property(&prop)) {
+		const char *name, *val;
+
+		val = ofnode_get_property_by_prop(&prop, &name, NULL);
+		env_set(name, val);
+	}
+}
+#endif