power: supply: core: Add power_supply_battery_info and API

power_supply_get_battery_info() reads battery data from devicetree.
struct power_supply_battery_info provides battery data to drivers.
Its fields correspond to elements in enum power_supply_property.
Drivers may surface battery data in sysfs via corresponding
POWER_SUPPLY_PROP_* fields.
Signed-off-by: Matt Ranostay <matt@ranostay.consulting>
Signed-off-by: Liam Breck <kernel@networkimprov.net>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>

Documentation/power/power_supply_class.txt

@@ -174,6 +174,18 @@ issued by external power supply will notify supplicants via
 external_power_changed callback.
 
 
+Devicetree battery characteristics
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Drivers should call power_supply_get_battery_info() to obtain battery
+characteristics from a devicetree battery node, defined in
+Documentation/devicetree/bindings/power/supply/battery.txt. This is
+implemented in drivers/power/supply/bq27xxx_battery.c.
+
+Properties in struct power_supply_battery_info and their counterparts in the
+battery node have names corresponding to elements in enum power_supply_property,
+for naming consistency between sysfs attributes and battery node properties.
+
+
 QA
 ~~
 Q: Where is POWER_SUPPLY_PROP_XYZ attribute?

drivers/power/supply/power_supply_core.c

@@ -17,6 +17,7 @@
 #include <linux/device.h>
 #include <linux/notifier.h>
 #include <linux/err.h>
+#include <linux/of.h>
 #include <linux/power_supply.h>
 #include <linux/thermal.h>
 #include "power_supply.h"
@@ -519,6 +520,62 @@ struct power_supply *devm_power_supply_get_by_phandle(struct device *dev,
 EXPORT_SYMBOL_GPL(devm_power_supply_get_by_phandle);
 #endif /* CONFIG_OF */
 
+int power_supply_get_battery_info(struct power_supply *psy,
+				  struct power_supply_battery_info *info)
+{
+	struct device_node *battery_np;
+	const char *value;
+	int err;
+
+	info->energy_full_design_uwh         = -EINVAL;
+	info->charge_full_design_uah         = -EINVAL;
+	info->voltage_min_design_uv          = -EINVAL;
+	info->precharge_current_ua           = -EINVAL;
+	info->charge_term_current_ua         = -EINVAL;
+	info->constant_charge_current_max_ua = -EINVAL;
+	info->constant_charge_voltage_max_uv = -EINVAL;
+
+	if (!psy->of_node) {
+		dev_warn(&psy->dev, "%s currently only supports devicetree\n",
+			 __func__);
+		return -ENXIO;
+	}
+
+	battery_np = of_parse_phandle(psy->of_node, "monitored-battery", 0);
+	if (!battery_np)
+		return -ENODEV;
+
+	err = of_property_read_string(battery_np, "compatible", &value);
+	if (err)
+		return err;
+
+	if (strcmp("simple-battery", value))
+		return -ENODEV;
+
+	/* The property and field names below must correspond to elements
+	 * in enum power_supply_property. For reasoning, see
+	 * Documentation/power/power_supply_class.txt.
+	 */
+
+	of_property_read_u32(battery_np, "energy-full-design-microwatt-hours",
+			     &info->energy_full_design_uwh);
+	of_property_read_u32(battery_np, "charge-full-design-microamp-hours",
+			     &info->charge_full_design_uah);
+	of_property_read_u32(battery_np, "voltage-min-design-microvolt",
+			     &info->voltage_min_design_uv);
+	of_property_read_u32(battery_np, "precharge-current-microamp",
+			     &info->precharge_current_ua);
+	of_property_read_u32(battery_np, "charge-term-current-microamp",
+			     &info->charge_term_current_ua);
+	of_property_read_u32(battery_np, "constant_charge_current_max_microamp",
+			     &info->constant_charge_current_max_ua);
+	of_property_read_u32(battery_np, "constant_charge_voltage_max_microvolt",
+			     &info->constant_charge_voltage_max_uv);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(power_supply_get_battery_info);
+
 int power_supply_get_property(struct power_supply *psy,
 			    enum power_supply_property psp,
 			    union power_supply_propval *val)

include/linux/power_supply.h

@@ -289,6 +289,25 @@ struct power_supply_info {
 	int use_for_apm;
 };
 
+/*
+ * This is the recommended struct to manage static battery parameters,
+ * populated by power_supply_get_battery_info(). Most platform drivers should
+ * use these for consistency.
+ * Its field names must correspond to elements in enum power_supply_property.
+ * The default field value is -EINVAL.
+ * Power supply class itself doesn't use this.
+ */
+
+struct power_supply_battery_info {
+	int energy_full_design_uwh;	    /* microWatt-hours */
+	int charge_full_design_uah;	    /* microAmp-hours */
+	int voltage_min_design_uv;	    /* microVolts */
+	int precharge_current_ua;	    /* microAmps */
+	int charge_term_current_ua;	    /* microAmps */
+	int constant_charge_current_max_ua; /* microAmps */
+	int constant_charge_voltage_max_uv; /* microVolts */
+};
+
 extern struct atomic_notifier_head power_supply_notifier;
 extern int power_supply_reg_notifier(struct notifier_block *nb);
 extern void power_supply_unreg_notifier(struct notifier_block *nb);
@@ -307,6 +326,9 @@ static inline struct power_supply *
 devm_power_supply_get_by_phandle(struct device *dev, const char *property)
 { return NULL; }
 #endif /* CONFIG_OF */
+
+extern int power_supply_get_battery_info(struct power_supply *psy,
+					 struct power_supply_battery_info *info);
 extern void power_supply_changed(struct power_supply *psy);
 extern int power_supply_am_i_supplied(struct power_supply *psy);
 extern int power_supply_set_battery_charged(struct power_supply *psy);