power: supply: Add power_supply_set_input_current_limit_from_supplier helper

On some devices the USB Type-C port power (USB PD 2.0) negotiation is
done by a separate port-controller IC, while the current limit is
controlled through another (charger) IC.

It has been decided to model this by modelling the external Type-C
power brick (adapter/charger) as a power-supply class device which
supplies the charger-IC, with its voltage-now and current-max representing
the negotiated voltage and max current draw.

This commit adds a power_supply_set_input_current_limit_from_supplier
helper function which charger power-supply drivers can call to get
the max-current from their supplier and have this applied
through their set_property call-back to their input-current-limit.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>

drivers/power/supply/power_supply_core.c

@@ -371,6 +371,47 @@ int power_supply_is_system_supplied(void)
 }
 EXPORT_SYMBOL_GPL(power_supply_is_system_supplied);
 
+static int __power_supply_get_supplier_max_current(struct device *dev,
+						   void *data)
+{
+	union power_supply_propval ret = {0,};
+	struct power_supply *epsy = dev_get_drvdata(dev);
+	struct power_supply *psy = data;
+
+	if (__power_supply_is_supplied_by(epsy, psy))
+		if (!epsy->desc->get_property(epsy,
+					      POWER_SUPPLY_PROP_CURRENT_MAX,
+					      &ret))
+			return ret.intval;
+
+	return 0;
+}
+
+int power_supply_set_input_current_limit_from_supplier(struct power_supply *psy)
+{
+	union power_supply_propval val = {0,};
+	int curr;
+
+	if (!psy->desc->set_property)
+		return -EINVAL;
+
+	/*
+	 * This function is not intended for use with a supply with multiple
+	 * suppliers, we simply pick the first supply to report a non 0
+	 * max-current.
+	 */
+	curr = class_for_each_device(power_supply_class, NULL, psy,
+				      __power_supply_get_supplier_max_current);
+	if (curr <= 0)
+		return (curr == 0) ? -ENODEV : curr;
+
+	val.intval = curr;
+
+	return psy->desc->set_property(psy,
+				POWER_SUPPLY_PROP_INPUT_CURRENT_LIMIT, &val);
+}
+EXPORT_SYMBOL_GPL(power_supply_set_input_current_limit_from_supplier);
+
 int power_supply_set_battery_charged(struct power_supply *psy)
 {
 	if (atomic_read(&psy->use_cnt) >= 0 &&

include/linux/power_supply.h

@@ -332,6 +332,8 @@ extern int power_supply_get_battery_info(struct power_supply *psy,
 					 struct power_supply_battery_info *info);
 extern void power_supply_changed(struct power_supply *psy);
 extern int power_supply_am_i_supplied(struct power_supply *psy);
+extern int power_supply_set_input_current_limit_from_supplier(
+					 struct power_supply *psy);
 extern int power_supply_set_battery_charged(struct power_supply *psy);
 
 #ifdef CONFIG_POWER_SUPPLY