power: supply: ab8500: Standardize BTI resistance

The Battery Type Indicator (BTI) resistor is a resistor mounted
between a special terminal on the battery and ground. By sending
a fixed current (such as 7mA) through this resistor and measuring
the voltage over it, the resistance can be determined, and this
verifies the battery type.

Typical side view of the battery:

  o     o     o
 GND   BTI   +3.8V

Typical example of the electrical layout:

  +3.8 V   BTI
    |       |
    | +     |
 _______   [ ] 7kOhm
   ___      |
    |       |
    |       |
   GND     GND

By verifying this resistance before attempting to charge the
battery we add an additional level of security.

In some systems this is used for plug-and-play of batteries with
different capacity. In other cases, this is merely used to verify
that the right type of battery is connected, if several batteries
have the same physical shape and can be plugged into the same
slot. Sometimes this is just a surplus security mechanism.

Nokia and Samsung among many other vendors are known to use these
BTI resistors.

Add the BTI properties to struct power_supply_battery_info and
switch the AB8500 charger code over to using it.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/include/linux/power_supply.h b/include/linux/power_supply.h
index f8601598d3d3..7fdc03cf2285 100644
--- a/include/linux/power_supply.h
+++ b/include/linux/power_supply.h
@@ -498,6 +498,14 @@ struct power_supply_maintenance_charge_table {
  *   by temperature: highest temperature with lowest resistance first, lowest
  *   temperature with highest resistance last.
  * @resist_table_size: the number of items in the resist_table.
+ * @bti_resistance_ohm: The Battery Type Indicator (BIT) nominal resistance
+ *   in ohms for this battery, if an identification resistor is mounted
+ *   between a third battery terminal and ground. This scheme is used by a lot
+ *   of mobile device batteries.
+ * @bti_resistance_tolerance: The tolerance in percent of the BTI resistance,
+ *   for example 10 for +/- 10%, if the bti_resistance is set to 7000 and the
+ *   tolerance is 10% we will detect a proper battery if the BTI resistance
+ *   is between 6300 and 7700 Ohm.
  *
  * This is the recommended struct to manage static battery parameters,
  * populated by power_supply_get_battery_info(). Most platform drivers should
@@ -624,6 +632,8 @@ struct power_supply_battery_info {
 	int ocv_table_size[POWER_SUPPLY_OCV_TEMP_MAX];
 	struct power_supply_resistance_temp_table *resist_table;
 	int resist_table_size;
+	int bti_resistance_ohm;
+	int bti_resistance_tolerance;
 };
 
 extern struct atomic_notifier_head power_supply_notifier;
@@ -667,6 +677,8 @@ power_supply_temp2resist_simple(struct power_supply_resistance_temp_table *table
 				int table_len, int temp);
 extern struct power_supply_maintenance_charge_table *
 power_supply_get_maintenance_charging_setting(struct power_supply_battery_info *info, int index);
+extern bool power_supply_battery_bti_in_range(struct power_supply_battery_info *info,
+					      int resistance);
 extern void power_supply_changed(struct power_supply *psy);
 extern int power_supply_am_i_supplied(struct power_supply *psy);
 int power_supply_get_property_from_supplier(struct power_supply *psy,
@@ -684,6 +696,7 @@ power_supply_supports_maintenance_charging(struct power_supply_battery_info *inf
 	return (mt != NULL);
 }
 
+
 #ifdef CONFIG_POWER_SUPPLY
 extern int power_supply_is_system_supplied(void);
 #else