power: supply: add charge_behaviour attributes

This a revised version of
"[RFC] add standardized attributes for force_discharge and inhibit_charge" [0],
incorporating discussion results.

The biggest change is the switch from two boolean attributes to a single
enum attribute.

[0] https://lore.kernel.org/platform-driver-x86/21569a89-8303-8573-05fb-c2fec29983d1@gmail.com/

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20211123232704.25394-2-linux@weissschuh.net
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

Documentation/ABI/testing/sysfs-class-power

@@ -455,6 +455,20 @@ Description:
 			      "Unknown", "Charging", "Discharging",
 			      "Not charging", "Full"
 
+What:		/sys/class/power_supply/<supply_name>/charge_behaviour
+Date:		November 2021
+Contact:	linux-pm@vger.kernel.org
+Description:
+		Represents the charging behaviour.
+
+		Access: Read, Write
+
+		Valid values:
+			================ ====================================
+			auto:            Charge normally, respect thresholds
+			inhibit-charge:  Do not charge while AC is attached
+			force-discharge: Force discharge while AC is attached
+
 What:		/sys/class/power_supply/<supply_name>/technology
 Date:		May 2007
 Contact:	linux-pm@vger.kernel.org

include/linux/power_supply.h

@@ -132,6 +132,7 @@ enum power_supply_property {
 	POWER_SUPPLY_PROP_CHARGE_CONTROL_LIMIT_MAX,
 	POWER_SUPPLY_PROP_CHARGE_CONTROL_START_THRESHOLD, /* in percents! */
 	POWER_SUPPLY_PROP_CHARGE_CONTROL_END_THRESHOLD, /* in percents! */
+	POWER_SUPPLY_PROP_CHARGE_BEHAVIOUR,
 	POWER_SUPPLY_PROP_INPUT_CURRENT_LIMIT,
 	POWER_SUPPLY_PROP_INPUT_VOLTAGE_LIMIT,
 	POWER_SUPPLY_PROP_INPUT_POWER_LIMIT,
@@ -202,6 +203,12 @@ enum power_supply_usb_type {
 	POWER_SUPPLY_USB_TYPE_APPLE_BRICK_ID,	/* Apple Charging Method */
 };
 
+enum power_supply_charge_behaviour {
+	POWER_SUPPLY_CHARGE_BEHAVIOUR_AUTO = 0,
+	POWER_SUPPLY_CHARGE_BEHAVIOUR_INHIBIT_CHARGE,
+	POWER_SUPPLY_CHARGE_BEHAVIOUR_FORCE_DISCHARGE,
+};
+
 enum power_supply_notifier_events {
 	PSY_EVENT_PROP_CHANGED,
 };