Custom charger_propval in out-of-tree driver

[nicogou]

Hi Zephyr community,

I am using an Arduino Nicla Sense ME on a project, which has a BQ25120A charger chip.
This chip has an LDO output that I need to configure via I2C. I defined a custom property the following way:

enum bq25120a_charger_property {
	BQ25120A_CHARGER_PROP_LDO_VALUE = CHARGER_PROP_CUSTOM_BEGIN,
};

Then in my implementation of the int charger_set_prop(const struct device *dev, const charger_prop_t prop, const union charger_propval *val); function I write the proper register. To test that it was working properly I used an unused member of charger_propval as the val argument. This hack worked fine for testing, but I am now wondering about the best way to add custom members to this union ?
I defined a custom union that I pass as argument instead of charger_propval:

union bq25120a_propval {
	union charger_propval;
	uint32_t ldo_value;
};

It works, but I get warnings of this type :
expected 'const union charger_propval *' but argument is of type 'const union bq25120a_propval *'

Does anyone have an idea on how I can proceed to remove this warning ?
Thanks
Nicolas G.