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, 7 insertions, 7 deletions

diff --git a/drivers/power/supply/ab8500_bmdata.c b/drivers/power/supply/ab8500_bmdata.c
index bf0b74773eee..3e6ea22372b2 100644
--- a/drivers/power/supply/ab8500_bmdata.c
+++ b/drivers/power/supply/ab8500_bmdata.c
@@ -73,12 +73,6 @@ static struct power_supply_maintenance_charge_table ab8500_maint_charg_table[] =
 	}
 };
 
-/* Default battery type for reference designs is the unknown type */
-static struct ab8500_battery_type bat_type_thermistor_unknown = {
-	.resis_high = 0,
-	.resis_low = 0,
-};
-
 static const struct ab8500_bm_capacity_levels cap_levels = {
 	.critical	= 2,
 	.low		= 10,
@@ -136,7 +130,6 @@ struct ab8500_bm_data ab8500_bm_data = {
 	.enable_overshoot       = false,
 	.fg_res                 = 100,
 	.cap_levels             = &cap_levels,
-	.bat_type               = &bat_type_thermistor_unknown,
 	.interval_charging      = 5,
 	.interval_not_charging  = 120,
 	.maxi                   = &ab8500_maxi_params,
@@ -214,6 +207,13 @@ int ab8500_bm_of_probe(struct power_supply *psy,
 		bi->resist_table_size = ARRAY_SIZE(temp_to_batres_tbl_thermistor);
 	}
 
+	/* The default battery is emulated by a resistor at 7K */
+	if (bi->bti_resistance_ohm < 0 ||
+	    bi->bti_resistance_tolerance < 0) {
+		bi->bti_resistance_ohm = 7000;
+		bi->bti_resistance_tolerance = 20;
+	}
+
 	if (!bi->ocv_table[0]) {
 		/* Default capacity table at say 25 degrees Celsius */
 		bi->ocv_temp[0] = 25;