power: supply: core: Add resistance power supply property

Some battery drivers provide the ability to export internal resistance
as a parameter. Add internal_resistance power supply property for that
purpose.

Signed-off-by: Fenglin Wu <[e-mail]>
Signed-off-by: Sebastian Reichel <[e-mail]>

Documentation/ABI/testing/sysfs-class-power

···
 			Integer > 0: representing full cycles
 			Integer = 0: cycle_count info is not available
 
+What:		/sys/class/power_supply/<supply_name>/internal_resistance
+Date:		August 2025
+Contact:	[e-mail]
+Description:
+		Represent the battery's internal resistance, often referred
+		to as Equivalent Series Resistance (ESR). It is a dynamic
+		parameter that reflects the opposition to current flow within
+		the cell. It is not a fixed value but varies significantly
+		based on several operational conditions, including battery
+		state of charge (SoC), temperature, and whether the battery
+		is in a charging or discharging state.
+
+		Access: Read
+
+		Valid values: Represented in microohms
+
 **USB Properties**
 
 What:		/sys/class/power_supply/<supply_name>/input_current_limit

drivers/power/supply/power_supply_sysfs.c

···
 	POWER_SUPPLY_ATTR(MANUFACTURE_YEAR),
 	POWER_SUPPLY_ATTR(MANUFACTURE_MONTH),
 	POWER_SUPPLY_ATTR(MANUFACTURE_DAY),
+	POWER_SUPPLY_ATTR(INTERNAL_RESISTANCE),
 	/* Properties of type `const char *' */
 	POWER_SUPPLY_ATTR(MODEL_NAME),
 	POWER_SUPPLY_ATTR(MANUFACTURER),

include/linux/power_supply.h

···
 	POWER_SUPPLY_PROP_MANUFACTURE_YEAR,
 	POWER_SUPPLY_PROP_MANUFACTURE_MONTH,
 	POWER_SUPPLY_PROP_MANUFACTURE_DAY,
+	POWER_SUPPLY_PROP_INTERNAL_RESISTANCE,
 	/* Properties of type `const char *' */
 	POWER_SUPPLY_PROP_MODEL_NAME,
 	POWER_SUPPLY_PROP_MANUFACTURER,