power_supply: Add driver private data

Allow drivers to store private data inside power_supply structure for
later usage in power supply operations.

Usage of driver private data is necessary to access driver's state
container object from power supply calls (like get_property()) if struct
'power_supply' is a stored there as a pointer, for example:

struct some_driver_info {
	struct i2c_client       *client;
	struct power_supply     *power_supply;
	...
}

In such case one cannot use container_of() and must store pointer to
state container as private data.
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Reviewed-by: Sebastian Reichel <sre@kernel.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Sebastian Reichel <sre@kernel.org>

drivers/power/power_supply_core.c

@@ -674,6 +674,12 @@ void power_supply_unregister(struct power_supply *psy)
 }
 EXPORT_SYMBOL_GPL(power_supply_unregister);
 
+void *power_supply_get_drvdata(struct power_supply *psy)
+{
+	return psy->drv_data;
+}
+EXPORT_SYMBOL_GPL(power_supply_get_drvdata);
+
 static int __init power_supply_class_init(void)
 {
 	power_supply_class = class_create(THIS_MODULE, "power_supply");

include/linux/power_supply.h

@@ -209,6 +209,9 @@ struct power_supply {
 	/* For APM emulation, think legacy userspace. */
 	int use_for_apm;
 
+	/* Driver private data */
+	void *drv_data;
+
 	/* private */
 	struct device *dev;
 	struct work_struct changed_work;
@@ -285,6 +288,7 @@ extern int devm_power_supply_register_no_ws(struct device *parent,
 extern void power_supply_unregister(struct power_supply *psy);
 extern int power_supply_powers(struct power_supply *psy, struct device *dev);
 
+extern void *power_supply_get_drvdata(struct power_supply *psy);
 /* For APM emulation, think legacy userspace. */
 extern struct class *power_supply_class;