[PATCH 4/5] env: allow default environment to be amended from control dtb

[Rasmus Villemoes]

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. To that end, allow the control dtb to contain
a /config/default-enviroment property, whose value will be used to
amend the default environment baked into the U-Boot binary itself.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes at prevas.dk>
---
 cmd/nvedit.c | 37 +++++++++++++++++++++++++++++++++++++
 env/Kconfig  | 21 +++++++++++++++++++++
 env/common.c | 19 +++++++++++++++++++
 3 files changed, 77 insertions(+)

diff --git a/cmd/nvedit.c b/cmd/nvedit.c
index 7fce723800..eda8b3b9d2 100644
--- a/cmd/nvedit.c
+++ b/cmd/nvedit.c
@@ -703,6 +703,39 @@ char *from_env(const char *envvar)
 	return ret;
 }
 
+static int env_get_f_fdt(const char *name, char *buf, unsigned len)
+{
+	const char *env;
+	int plen, nlen, n;
+
+	if (!IS_ENABLED(CONFIG_ENV_AMEND_DEFAULT_FROM_FDT))
+		return 0;
+
+	env = fdtdec_get_config_property(gd->fdt_blob, "default-environment",
+					 &plen);
+	if (!env)
+		return 0;
+
+	nlen = strlen(name);
+	while (plen > nlen) {
+		if (memcmp(name, env, nlen) == 0 && env[nlen] == '=') {
+			/* Found. Copy value. */
+			n = strlcpy(buf, &env[nlen + 1], len);
+			if (n < len)
+				return n;
+
+			printf("env_buf [%u bytes] too small for value of \"%s\"\n",
+			       len, name);
+			return len;
+		}
+		/* Skip this key=val pair. */
+		n = strlen(env) + 1;
+		plen -= n;
+		env += n;
+	}
+	return 0;
+}
+
 /*
  * Look up variable from environment for restricted C runtime env.
  */
@@ -710,6 +743,10 @@ int env_get_f(const char *name, char *buf, unsigned len)
 {
 	int i, nxt, c;
 
+	i = env_get_f_fdt(name, buf, len);
+	if (i)
+		return i;
+
 	for (i = 0; env_get_char(i) != '\0'; i = nxt + 1) {
 		int val, n;
 
diff --git a/env/Kconfig b/env/Kconfig
index 67ce93061b..66bbac42c7 100644
--- a/env/Kconfig
+++ b/env/Kconfig
@@ -646,6 +646,27 @@ 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_AMEND_DEFAULT_FROM_FDT
+	bool "Amend default environment by /config/default-environment property"
+	depends on OF_CONTROL
+	help
+	  The default environment built into the U-Boot binary is a
+	  static array defined from various CONFIG_ options, or via
+	  CONFIG_DEFAULT_ENV_FILE. Selecting this option means that
+	  whenever that default environment is used (either for
+	  populating the initial environment, or for resetting
+	  specific variables to their default value), the device tree
+	  property /config/default-environment is also consulted, and
+	  values found there have precedence over those in the static
+	  array. That property should be a series of "key=value"
+	  pairs, e.g.
+
+	  /config {
+	      default-environment = "ipaddr=1.2.3.4",
+	                            "bootcmd=tftp $loadaddr foo.itb; bootm $loadaddr",
+				    "bootdelay=5";
+	  }
+
 config ENV_APPEND
 	bool "Always append the environment with new data"
 	default n
diff --git a/env/common.c b/env/common.c
index 7363da849b..8d0e45fde6 100644
--- a/env/common.c
+++ b/env/common.c
@@ -63,6 +63,22 @@ char *env_get_default(const char *name)
 	return ret_val;
 }
 
+static void env_amend_default_from_fdt(int flags, int nvars, char *const vars[])
+{
+	const void *val;
+	int len;
+
+	if (!IS_ENABLED(CONFIG_ENV_AMEND_DEFAULT_FROM_FDT))
+		return;
+
+	val = fdtdec_get_config_property(gd->fdt_blob, "default-environment",
+					 &len);
+	if (!val)
+		return;
+
+	himport_r(&env_htab, val, len, '\0', flags, 0, nvars, vars);
+}
+
 void env_set_default(const char *s, int flags)
 {
 	if (sizeof(default_environment) > ENV_SIZE) {
@@ -88,6 +104,8 @@ void env_set_default(const char *s, int flags)
 		pr_err("## Error: Environment import failed: errno = %d\n",
 		       errno);
 
+	env_amend_default_from_fdt(flags | H_NOCLEAR, 0, NULL);
+
 	gd->flags |= GD_FLG_ENV_READY;
 	gd->flags |= GD_FLG_ENV_DEFAULT;
 }
@@ -104,6 +122,7 @@ void env_set_default_vars(int nvars, char * const vars[], int flags)
 	himport_r(&env_htab, (const char *)default_environment,
 				sizeof(default_environment), '\0',
 				flags, 0, nvars, vars);
+	env_amend_default_from_fdt(flags, nvars, vars);
 }
 
 /*
-- 
2.23.0