ACPI / battery: fix wrong value of capacity_now reported when fully charged

It seems that some batteries (noticed on DELL JYPJ136) assume
capacity_now = design_capacity when fully charged. This causes
reported capacity to suddenly jump to >full_charge_capacity (and that
means capacity reported to userspace is >100% and incorrect)
values after 99%. This patch detects capacity_now > full_charge_capacity,
notifies userspace (unless it is the known bug where capacity_now ==
design_capacity) and trims the value to full_charge_capacity.
Signed-off-by: Josef Gajdusek <atx@atx.name>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/battery.c

@@ -535,6 +535,20 @@ static int acpi_battery_get_state(struct acpi_battery *battery)
 			" invalid.\n");
 	}
 
+	/*
+	 * When fully charged, some batteries wrongly report
+	 * capacity_now = design_capacity instead of = full_charge_capacity
+	 */
+	if (battery->capacity_now > battery->full_charge_capacity
+	    && battery->full_charge_capacity != ACPI_BATTERY_VALUE_UNKNOWN) {
+		battery->capacity_now = battery->full_charge_capacity;
+		if (battery->capacity_now != battery->design_capacity)
+			printk_once(KERN_WARNING FW_BUG
+				"battery: reported current charge level (%d) "
+				"is higher than reported maximum charge level (%d).\n",
+				battery->capacity_now, battery->full_charge_capacity);
+	}
+
 	if (test_bit(ACPI_BATTERY_QUIRK_PERCENTAGE_CAPACITY, &battery->flags)
 	    && battery->capacity_now >= 0 && battery->capacity_now <= 100)
 		battery->capacity_now = (battery->capacity_now *