ACPI: battery: do not export degraded capacity values over 100

With a degraded battery, full_charge_capacity can be less
than design_capacity, however it's not sure that capacity_now's
max will follow.

Example from an affected machine:
/sys/class/power_supply/BAT0/charge_full        -> 4290000
/sys/class/power_supply/BAT0/charge_full_design -> 5900000
/sys/class/power_supply/BAT0/charge_now         -> 5900000
/sys/class/power_supply/BAT0/capacity           -> 137

The battery is a degraded one with a full charge, and
charge_now is the value of charge_full_design instead of
charge_full.

Added a new quirk to test and correct this, and
a new function to check if the battery is a degraded one
or not. This keeps the possibility to be over 100 if
it's really the case.

Signed-off-by: Laszlo Toth <laszlth@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/battery.c

@@ -121,6 +121,10 @@ enum {
 	   post-1.29 BIOS), but as of Nov. 2012, no such update is
 	   available for the 2010 models.  */
 	ACPI_BATTERY_QUIRK_THINKPAD_MAH,
+	/* for batteries reporting current capacity with design capacity
+	 * on a full charge, but showing degradation in full charge cap.
+	 */
+	ACPI_BATTERY_QUIRK_DEGRADED_FULL_CHARGE,
 };
 
 struct acpi_battery {
@@ -207,6 +211,12 @@ static int acpi_battery_is_charged(struct acpi_battery *battery)
 	return 0;
 }
 
+static bool acpi_battery_is_degraded(struct acpi_battery *battery)
+{
+	return battery->full_charge_capacity && battery->design_capacity &&
+		battery->full_charge_capacity < battery->design_capacity;
+}
+
 static int acpi_battery_get_property(struct power_supply *psy,
 				     enum power_supply_property psp,
 				     union power_supply_propval *val)
@@ -483,6 +493,10 @@ static int extract_battery_info(const int use_bix,
 		   it's impossible to tell if they would need an adjustment
 		   or not if their values were higher.  */
 	}
+	if (test_bit(ACPI_BATTERY_QUIRK_DEGRADED_FULL_CHARGE, &battery->flags) &&
+	    battery->capacity_now > battery->full_charge_capacity)
+		battery->capacity_now = battery->full_charge_capacity;
+
 	return result;
 }
 
@@ -575,6 +589,10 @@ static int acpi_battery_get_state(struct acpi_battery *battery)
 		battery->capacity_now = battery->capacity_now *
 		    10000 / battery->design_voltage;
 	}
+	if (test_bit(ACPI_BATTERY_QUIRK_DEGRADED_FULL_CHARGE, &battery->flags) &&
+	    battery->capacity_now > battery->full_charge_capacity)
+		battery->capacity_now = battery->full_charge_capacity;
+
 	return result;
 }
 
@@ -885,6 +903,15 @@ static void acpi_battery_quirks(struct acpi_battery *battery)
 			}
 		}
 	}
+
+	if (test_bit(ACPI_BATTERY_QUIRK_DEGRADED_FULL_CHARGE, &battery->flags))
+		return;
+
+	if (acpi_battery_is_degraded(battery) &&
+	    battery->capacity_now > battery->full_charge_capacity) {
+		set_bit(ACPI_BATTERY_QUIRK_DEGRADED_FULL_CHARGE, &battery->flags);
+		battery->capacity_now = battery->full_charge_capacity;
+	}
 }
 
 static int acpi_battery_update(struct acpi_battery *battery, bool resume)