common: don't fixup empty serial/machine_compatible strings

There is no point in fixing up an empty string into the kernel device
tree, yet this can happen when globalvar_add_simple_string() is called
for the variable at least once as the function replaces NULL with an
allocated empty string. globalvar_add_simple_string() was called
unconditionally for of.kernel.add_machine_compatible, which in turn
led to always fixing up an empty string as the top-most compatible.

Resolve this by having barebox_get_(of_machine_compatible|serial_number)
return NULL for the empty string as well.

Fixes: 81dd24a0946c ("of: add generic of_prepend_machine_compatible()")
Fixes: f6756e9ce6f2 ("common: add $global.serial_number with device tree fixup")
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20220718114824.2632364-2-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 4 insertions, 0 deletions

diff --git a/common/misc.c b/common/misc.c
index 0f6de3e9e5..e0e32f47c5 100644
--- a/common/misc.c
+++ b/common/misc.c
@@ -191,6 +191,8 @@ void barebox_set_serial_number(const char *__serial_number)
 
 const char *barebox_get_serial_number(void)
 {
+	if (!serial_number || *serial_number == '\0')
+		return NULL;
 	return serial_number;
 }
 
@@ -204,6 +206,8 @@ void barebox_set_of_machine_compatible(const char *__compatible)
 
 const char *barebox_get_of_machine_compatible(void)
 {
+	if (!of_machine_compatible || *of_machine_compatible == '\0')
+		return NULL;
 	return of_machine_compatible;
 }