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>

2 files changed, 48 insertions, 0 deletions

diff --git a/env/Kconfig b/env/Kconfig
index 1b7906cf726..1411f9e815e 100644
--- a/env/Kconfig
+++ b/env/Kconfig
@@ -670,6 +670,24 @@ config DELAY_ENVIRONMENT
 	  later by U-Boot code. With CONFIG_OF_CONTROL this is instead
 	  controlled by the value of /config/load-environment.
 
+config ENV_IMPORT_FDT
+	bool "Amend environment by FDT properties"
+	depends on OF_CONTROL
+	help
+	  If selected, after the environment has been loaded from its
+	  persistent location, the "env_fdt_path" variable is looked
+	  up and used as a path to a node in the control DTB. The
+	  property/value pairs in that node is then used to update the
+	  run-time environment. This can be useful to use the same
+	  U-Boot binary with different board variants.
+
+config ENV_FDT_PATH
+	string "Default value for env_fdt_path variable"
+	depends on ENV_IMPORT_FDT
+	default "/config/environment"
+	help
+	  The initial value of the env_fdt_path variable.
+
 config ENV_APPEND
 	bool "Always append the environment with new data"
 	default n
diff --git a/env/common.c b/env/common.c
index 49bbb05eece..81e9e0b2aaf 100644
--- a/env/common.c
+++ b/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