power: supply: bq25890: Add support for having a secondary charger IC

Some devices, such as the Lenovo Yoga Tab 3 Pro (YT3-X90F) have multiple
batteries with a separate bq25890 charger for each battery.

This requires some coordination between the chargers specifically
the main charger needs to put the secondary charger in Hi-Z mode when:

1. Enabling its 5V boost (OTG) output to power an external USB device,
to avoid the secondary charger IC seeing this as external Vbus and
then trying to charge the secondary battery from this.

2. Talking the Pump Express protocol to increase the external Vbus voltage.
Having the secondary charger drawing current when the main charger is
trying to talk the Pump Express protocol results in the external Vbus
voltage not being raised.

Add a new "linux,secondary-charger-name" string device-property, which
can be set to the power_supply class device's name of the secondary
charger when there is a secondary charger; and make the Vbus regulator and
Pump Express code put the secondary charger in Hi-Z mode when necessary.

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: Marek Vasut <[e-mail]>
Signed-off-by: Hans de Goede <[e-mail]>
Signed-off-by: Sebastian Reichel <[e-mail]>

drivers/power/supply/bq25890_charger.c

···
 	struct i2c_client *client;
 	struct device *dev;
 	struct power_supply *charger;
+	struct power_supply *secondary_chrg;
 	struct power_supply_desc desc;
 	char name[28]; /* "bq25890-charger-%d" */
 	int id;
···
 {
 	struct bq25890_device *bq =
 		container_of(data, struct bq25890_device, pump_express_work.work);
+	union power_supply_propval value;
 	int voltage, i, ret;
 
 	dev_dbg(bq->dev, "Start to request input voltage increasing\n");
+
+	/* If there is a second charger put in Hi-Z mode */
+	if (bq->secondary_chrg) {
+		value.intval = 0;
+		power_supply_set_property(bq->secondary_chrg, POWER_SUPPLY_PROP_ONLINE, &value);
+	}
 
 	/* Enable current pulse voltage control protocol */
 	ret = bq25890_field_write(bq, F_PUMPX_EN, 1);
···
 	}
 
 	bq25890_field_write(bq, F_PUMPX_EN, 0);
+
+	if (bq->secondary_chrg) {
+		value.intval = 1;
+		power_supply_set_property(bq->secondary_chrg, POWER_SUPPLY_PROP_ONLINE, &value);
+	}
 
 	dev_info(bq->dev, "Hi-voltage charging requested, input voltage is %d mV\n",
 		 voltage);
···
 static int bq25890_vbus_enable(struct regulator_dev *rdev)
 {
 	struct bq25890_device *bq = rdev_get_drvdata(rdev);
+	union power_supply_propval val = {
+		.intval = 0,
+	};
+
+	/*
+	 * When enabling 5V boost / Vbus output, we need to put the secondary
+	 * charger in Hi-Z mode to avoid it trying to charge the secondary
+	 * battery from the 5V boost output.
+	 */
+	if (bq->secondary_chrg)
+		power_supply_set_property(bq->secondary_chrg, POWER_SUPPLY_PROP_ONLINE, &val);
 
 	return bq25890_set_otg_cfg(bq, 1);
 }
···
 static int bq25890_vbus_disable(struct regulator_dev *rdev)
 {
 	struct bq25890_device *bq = rdev_get_drvdata(rdev);
+	union power_supply_propval val = {
+		.intval = 1,
+	};
+	int ret;
 
-	return bq25890_set_otg_cfg(bq, 0);
+	ret = bq25890_set_otg_cfg(bq, 0);
+	if (ret)
+		return ret;
+
+	if (bq->secondary_chrg)
+		power_supply_set_property(bq->secondary_chrg, POWER_SUPPLY_PROP_ONLINE, &val);
+
+	return 0;
 }
 
 static int bq25890_vbus_is_enabled(struct regulator_dev *rdev)
···
 {
 	int ret;
 	struct bq25890_init_data *init = &bq->init_data;
+	const char *str;
+
+	ret = device_property_read_string(bq->dev, "linux,secondary-charger-name", &str);
+	if (ret == 0) {
+		bq->secondary_chrg = power_supply_get_by_name(str);
+		if (!bq->secondary_chrg)
+			return -EPROBE_DEFER;
+	}
 
 	/* Optional, left at 0 if property is not present */
 	device_property_read_u32(bq->dev, "linux,pump-express-vbus-max",