ds2760_battery: implement set_charged() feature

The ds2760's internal current meter is not reliable enough as it has an
inacurracy of around ~15%. Without any correction for that error, the
current accumulator is couting up all the time, even though the battery
is already fully charged and hence destroys the static information. The
longer it is connected, the worse is the aberration.

Fortunately, this can be corrected by the DS2760_CURRENT_OFFSET_BIAS
register. Using the external power_supply_set_battery_charged()
function, this register is now gauging the measurement.

A delayed work is used to debounce flaky GPIO signals and to let the
current value settle. Also see Maxim's application note AN4188.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Cc: Szabolcs Gyurko <szabolcs.gyurko@tlt.hu>
Cc: Matt Reimer <mreimer@vpop.net>
Cc: Anton Vorontsov <cbou@mail.ru>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>

drivers/power/ds2760_battery.c

@@ -56,6 +56,7 @@ struct ds2760_device_info {
 	struct device *w1_dev;
 	struct workqueue_struct *monitor_wqueue;
 	struct delayed_work monitor_work;
+	struct delayed_work set_charged_work;
 };
 
 static unsigned int cache_time = 1000;
@@ -327,6 +328,52 @@ static void ds2760_battery_external_power_changed(struct power_supply *psy)
 	queue_delayed_work(di->monitor_wqueue, &di->monitor_work, HZ/10);
 }
 
+
+static void ds2760_battery_set_charged_work(struct work_struct *work)
+{
+	char bias;
+	struct ds2760_device_info *di = container_of(work,
+		struct ds2760_device_info, set_charged_work.work);
+
+	dev_dbg(di->dev, "%s\n", __func__);
+
+	ds2760_battery_read_status(di);
+
+	/* When we get notified by external circuitry that the battery is
+	 * considered fully charged now, we know that there is no current
+	 * flow any more. However, the ds2760's internal current meter is
+	 * too inaccurate to rely on - spec say something ~15% failure.
+	 * Hence, we use the current offset bias register to compensate
+	 * that error.
+	 */
+
+	if (!power_supply_am_i_supplied(&di->bat))
+		return;
+
+	bias = (signed char) di->current_raw +
+		(signed char) di->raw[DS2760_CURRENT_OFFSET_BIAS];
+
+	dev_dbg(di->dev, "%s: bias = %d\n", __func__, bias);
+
+	w1_ds2760_write(di->w1_dev, &bias, DS2760_CURRENT_OFFSET_BIAS, 1);
+	w1_ds2760_store_eeprom(di->w1_dev, DS2760_EEPROM_BLOCK1);
+	w1_ds2760_recall_eeprom(di->w1_dev, DS2760_EEPROM_BLOCK1);
+
+	/* Write to the di->raw[] buffer directly - the CURRENT_OFFSET_BIAS
+	 * value won't be read back by ds2760_battery_read_status() */
+	di->raw[DS2760_CURRENT_OFFSET_BIAS] = bias;
+}
+
+static void ds2760_battery_set_charged(struct power_supply *psy)
+{
+	struct ds2760_device_info *di = to_ds2760_device_info(psy);
+
+	/* postpone the actual work by 20 secs. This is for debouncing GPIO
+	 * signals and to let the current value settle. See AN4188. */
+	cancel_delayed_work(&di->set_charged_work);
+	queue_delayed_work(di->monitor_wqueue, &di->set_charged_work, HZ * 20);
+}
+
 static int ds2760_battery_get_property(struct power_supply *psy,
 				       enum power_supply_property psp,
 				       union power_supply_propval *val)
@@ -412,6 +459,7 @@ static int ds2760_battery_probe(struct platform_device *pdev)
 	di->bat.properties	= ds2760_battery_props;
 	di->bat.num_properties	= ARRAY_SIZE(ds2760_battery_props);
 	di->bat.get_property	= ds2760_battery_get_property;
+	di->bat.set_charged	= ds2760_battery_set_charged;
 	di->bat.external_power_changed =
 				  ds2760_battery_external_power_changed;
 
@@ -443,6 +491,8 @@ static int ds2760_battery_probe(struct platform_device *pdev)
 	}
 
 	INIT_DELAYED_WORK(&di->monitor_work, ds2760_battery_work);
+	INIT_DELAYED_WORK(&di->set_charged_work,
+			  ds2760_battery_set_charged_work);
 	di->monitor_wqueue = create_singlethread_workqueue(dev_name(&pdev->dev));
 	if (!di->monitor_wqueue) {
 		retval = -ESRCH;
@@ -467,6 +517,8 @@ static int ds2760_battery_remove(struct platform_device *pdev)
 
 	cancel_rearming_delayed_workqueue(di->monitor_wqueue,
 					  &di->monitor_work);
+	cancel_rearming_delayed_workqueue(di->monitor_wqueue,
+					  &di->set_charged_work);
 	destroy_workqueue(di->monitor_wqueue);
 	power_supply_unregister(&di->bat);