power: supply: bq25890: Add support to read back the settings from the chip

On most x86/ACPI devices there is no devicetree to supply the necessary
init-data. Instead the firmware already fully initializes the bq25890
charger at boot. To support this, add support for reading back the
settings from the chip through a new "linux,read-back-settings" boolean.

So far this new property is only used on x86/ACPI (non devicetree) devs,
IOW it is not used in actual devicetree files. The devicetree-bindings
maintainers have requested properties like these to not be added to the
devicetree-bindings, so the new property is deliberately not added
to the existing devicetree-bindings.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/bq25890_charger.c

@@ -111,6 +111,7 @@ struct bq25890_device {
 	struct regmap_field *rmap_fields[F_MAX_FIELDS];
 
 	bool skip_reset;
+	bool read_back_init_data;
 	enum bq25890_chip_version chip_version;
 	struct bq25890_init_data init_data;
 	struct bq25890_state state;
@@ -696,7 +697,7 @@ static int bq25890_chip_reset(struct bq25890_device *bq)
 
 static int bq25890_rw_init_data(struct bq25890_device *bq)
 {
-	bool write = true;
+	bool write = !bq->read_back_init_data;
 	int ret;
 	int i;
 
@@ -981,6 +982,10 @@ static int bq25890_fw_probe(struct bq25890_device *bq)
 	struct bq25890_init_data *init = &bq->init_data;
 
 	bq->skip_reset = device_property_read_bool(bq->dev, "linux,skip-reset");
+	bq->read_back_init_data = device_property_read_bool(bq->dev,
+						"linux,read-back-settings");
+	if (bq->read_back_init_data)
+		return 0;
 
 	ret = bq25890_fw_read_u32_props(bq);
 	if (ret < 0)