[PATCH 1/2] blspec: allow board files to overwrite config file settings

[Marco Felsch]

This commit adds the support to overwrite and/or adapt blspec config
files by the following global variables:
  - global.blspec.fixup.devicetree
  - global.blspec.fixup.initrd
  - global.blspec.fixup.options
  - global.blspec.fixup.linux
  - global.blspec.fixup.devicetree-overlay.

Overwriting blspec-config's shouldn't be the normal case but there are
cases where this support is needed. One use-case can be a special
handling during update. E.g. the normal boot-flow don't need the initrd
but the update-flow uses it because the update system is on the initrd.
Another use-case could be a dynamic devicetree-overlay handling. E.g.
the board code dynamically checks which periphery boards are connected
and adds the required overlays dynamically.

A warning is printed if a already set option is overwritten to identify
unintended wrong boot behaviour early.

Signed-off-by: Marco Felsch <m.felsch at pengutronix.de>
---
 common/blspec.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/common/blspec.c b/common/blspec.c
index a07343f427..b527731a27 100644
--- a/common/blspec.c
+++ b/common/blspec.c
@@ -210,12 +210,21 @@ err_out:
  */
 const char *blspec_entry_var_get(struct blspec_entry *entry, const char *name)
 {
+	const char *match, *fixup;
 	const char *str;
 	int ret;
 
 	ret = of_property_read_string(entry->node, name, &str);
 
-	return ret ? NULL : str;
+	/* Check user specific overrides */
+	match = basprintf("global.blspec.fixup.%s", name);
+	fixup = getenv_nonempty(match);
+	free((void *)match);
+
+	if (!ret && fixup)
+		pr_warn("Overwrite %s blspec entry by fixup\n", name);
+
+	return fixup ? fixup : (ret ? NULL : str);
 }
 
 static void blspec_entry_free(struct bootentry *be)
-- 
2.20.1