[BATTERY] Universal power supply class (was: battery class)

This class is result of "external power" and "battery" classes merge,
as suggested by David Woodhouse. He also implemented uevent support.

Here how userspace seeing it now:

    	# ls /sys/class/power\ supply/
    	ac  main-battery  usb

    	# cat /sys/class/power\ supply/ac/type
    	AC

    	# cat /sys/class/power\ supply/usb/type
    	USB

    	# cat /sys/class/power\ supply/main-battery/type
    	Battery

    	# cat /sys/class/power\ supply/ac/online
    	1

    	# cat /sys/class/power\ supply/usb/online
    	0

    	# cat /sys/class/power\ supply/main-battery/status
    	Charging

    	# cat /sys/class/leds/h5400\:red-left/trigger
    	none h5400-radio timer hwtimer ac-online usb-online
    	main-battery-charging-or-full [main-battery-charging]
    	main-battery-full
Signed-off-by: Anton Vorontsov <cbou@mail.ru>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Documentation/power_supply_class.txt

+Linux power supply class
+========================
+
+Synopsis
+~~~~~~~~
+Power supply class used to represent battery, UPS, AC or DC power supply
+properties to user-space.
+
+It defines core set of attributes, which should be applicable to (almost)
+every power supply out there. Attributes are available via sysfs and uevent
+interfaces.
+
+Each attribute has well defined meaning, up to unit of measure used. While
+the attributes provided are believed to be universally applicable to any
+power supply, specific monitoring hardware may not be able to provide them
+all, so any of them may be skipped.
+
+Power supply class is extensible, and allows to define drivers own attributes.
+The core attribute set is subject to the standard Linux evolution (i.e.
+if it will be found that some attribute is applicable to many power supply
+types or their drivers, it can be added to the core set).
+
+It also integrates with LED framework, for the purpose of providing
+typically expected feedback of battery charging/fully charged status and
+AC/USB power supply online status. (Note that specific details of the
+indication (including whether to use it at all) are fully controllable by
+user and/or specific machine defaults, per design principles of LED
+framework).
+
+
+Attributes/properties
+~~~~~~~~~~~~~~~~~~~~~
+Power supply class has predefined set of attributes, this eliminates code
+duplication across drivers. Power supply class insist on reusing its
+predefined attributes *and* their units.
+
+So, userspace gets predictable set of attributes and their units for any
+kind of power supply, and can process/present them to a user in consistent
+manner. Results for different power supplies and machines are also directly
+comparable.
+
+See drivers/power/ds2760_battery.c and drivers/power/pda_power.c for the
+example how to declare and handle attributes.
+
+
+Units
+~~~~~
+Quoting include/linux/power_supply.h:
+
+  All voltages, currents, charges, energies, time and temperatures in µV,
+  µA, µAh, µWh, seconds and tenths of degree Celsius unless otherwise
+  stated. It's driver's job to convert its raw values to units in which
+  this class operates.
+
+
+Attributes/properties detailed
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+~ ~ ~ ~ ~ ~ ~  Charge/Energy/Capacity - how to not confuse  ~ ~ ~ ~ ~ ~ ~
+~                                                                       ~
+~ Because both "charge" (µAh) and "energy" (µWh) represents "capacity"  ~
+~ of battery, this class distinguish these terms. Don't mix them!       ~
+~                                                                       ~
+~ CHARGE_* attributes represents capacity in µAh only.                  ~
+~ ENERGY_* attributes represents capacity in µWh only.                  ~
+~ CAPACITY attribute represents capacity in *percents*, from 0 to 100.  ~
+~                                                                       ~
+~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
+
+Postfixes:
+_AVG - *hardware* averaged value, use it if your hardware is really able to
+report averaged values.
+_NOW - momentary/instantaneous values.
+
+STATUS - this attribute represents operating status (charging, full,
+discharging (i.e. powering a load), etc.). This corresponds to
+BATTERY_STATUS_* values, as defined in battery.h.
+
+HEALTH - represents health of the battery, values corresponds to
+POWER_SUPPLY_HEALTH_*, defined in battery.h.
+
+VOLTAGE_MAX_DESIGN, VOLTAGE_MIN_DESIGN - design values for maximal and
+minimal power supply voltages. Maximal/minimal means values of voltages
+when battery considered "full"/"empty" at normal conditions. Yes, there is
+no direct relation between voltage and battery capacity, but some dumb
+batteries use voltage for very approximated calculation of capacity.
+Battery driver also can use this attribute just to inform userspace
+about maximal and minimal voltage thresholds of a given battery.
+
+CHARGE_FULL_DESIGN, CHARGE_EMPTY_DESIGN - design charge values, when
+battery considered full/empty.
+
+ENERGY_FULL_DESIGN, ENERGY_EMPTY_DESIGN - same as above but for energy.
+
+CHARGE_FULL, CHARGE_EMPTY - These attributes means "last remembered value
+of charge when battery became full/empty". It also could mean "value of
+charge when battery considered full/empty at given conditions (temperature,
+age)". I.e. these attributes represents real thresholds, not design values.
+
+ENERGY_FULL, ENERGY_EMPTY - same as above but for energy.
+
+CAPACITY - capacity in percents.
+CAPACITY_LEVEL - capacity level. This corresponds to
+POWER_SUPPLY_CAPACITY_LEVEL_*.
+
+TEMP - temperature of the power supply.
+TEMP_AMBIENT - ambient temperature.
+
+TIME_TO_EMPTY - seconds left for battery to be considered empty (i.e.
+while battery powers a load)
+TIME_TO_FULL - seconds left for battery to be considered full (i.e.
+while battery is charging)
+
+
+Battery <-> external power supply interaction
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Often power supplies are acting as supplies and supplicants at the same
+time. Batteries are good example. So, batteries usually care if they're
+externally powered or not.
+
+For that case, power supply class implements notification mechanism for
+batteries.
+
+External power supply (AC) lists supplicants (batteries) names in
+"supplied_to" struct member, and each power_supply_changed() call
+issued by external power supply will notify supplicants via
+external_power_changed callback.
+
+
+QA
+~~
+Q: Where is POWER_SUPPLY_PROP_XYZ attribute?
+A: If you cannot find attribute suitable for your driver needs, feel free
+   to add it and send patch along with your driver.
+
+   The attributes available currently are the ones currently provided by the
+   drivers written.
+
+   Good candidates to add in future: model/part#, cycle_time, manufacturer,
+   etc.
+
+
+Q: I have some very specific attribute (e.g. battery color), should I add
+   this attribute to standard ones?
+A: Most likely, no. Such attribute can be placed in the driver itself, if
+   it is useful. Of course, if the attribute in question applicable to
+   large set of batteries, provided by many drivers, and/or comes from
+   some general battery specification/standard, it may be a candidate to
+   be added to the core attribute set.
+
+
+Q: Suppose, my battery monitoring chip/firmware does not provides capacity
+   in percents, but provides charge_{now,full,empty}. Should I calculate
+   percentage capacity manually, inside the driver, and register CAPACITY
+   attribute? The same question about time_to_empty/time_to_full.
+A: Most likely, no. This class is designed to export properties which are
+   directly measurable by the specific hardware available.
+
+   Inferring not available properties using some heuristics or mathematical
+   model is not subject of work for a battery driver. Such functionality
+   should be factored out, and in fact, apm_power, the driver to serve
+   legacy APM API on top of power supply class, uses a simple heuristic of
+   approximating remaining battery capacity based on its charge, current,
+   voltage and so on. But full-fledged battery model is likely not subject
+   for kernel at all, as it would require floating point calculation to deal
+   with things like differential equations and Kalman filters. This is
+   better be handled by batteryd/libbattery, yet to be written.

drivers/Kconfig

@@ -54,6 +54,8 @@ source "drivers/spi/Kconfig"
 
 source "drivers/w1/Kconfig"
 
+source "drivers/power/Kconfig"
+
 source "drivers/hwmon/Kconfig"
 
 source "drivers/mfd/Kconfig"

drivers/Makefile

@@ -61,6 +61,7 @@ obj-$(CONFIG_I2O)		+= message/
 obj-$(CONFIG_RTC_LIB)		+= rtc/
 obj-y				+= i2c/
 obj-$(CONFIG_W1)		+= w1/
+obj-$(CONFIG_POWER_SUPPLY)	+= power/
 obj-$(CONFIG_HWMON)		+= hwmon/
 obj-$(CONFIG_PHONE)		+= telephony/
 obj-$(CONFIG_MD)		+= md/

drivers/power/Kconfig

+menuconfig POWER_SUPPLY
+	tristate "Power supply class support"
+	help
+	  Say Y here to enable power supply class support. This allows
+	  power supply (batteries, AC, USB) monitoring by userspace
+	  via sysfs and uevent (if available) and/or APM kernel interface
+	  (if selected below).
+
+if POWER_SUPPLY
+
+config POWER_SUPPLY_DEBUG
+	bool "Power supply debug"
+	help
+	  Say Y here to enable debugging messages for power supply class
+	  and drivers.
+
+endif # POWER_SUPPLY

drivers/power/Makefile

+power_supply-objs := power_supply_core.o
+
+ifeq ($(CONFIG_SYSFS),y)
+power_supply-objs += power_supply_sysfs.o
+endif
+
+ifeq ($(CONFIG_LEDS_TRIGGERS),y)
+power_supply-objs += power_supply_leds.o
+endif
+
+ifeq ($(CONFIG_POWER_SUPPLY_DEBUG),y)
+EXTRA_CFLAGS += -DDEBUG
+endif
+
+obj-$(CONFIG_POWER_SUPPLY)	+= power_supply.o

drivers/power/power_supply.h

+/*
+ *  Functions private to power supply class
+ *
+ *  Copyright © 2007  Anton Vorontsov <cbou@mail.ru>
+ *  Copyright © 2004  Szabolcs Gyurko
+ *  Copyright © 2003  Ian Molton <spyro@f2s.com>
+ *
+ *  Modified: 2004, Oct     Szabolcs Gyurko
+ *
+ *  You may use this code as per GPL version 2
+ */
+
+#ifdef CONFIG_SYSFS
+
+extern int power_supply_create_attrs(struct power_supply *psy);
+extern void power_supply_remove_attrs(struct power_supply *psy);
+extern int power_supply_uevent(struct device *dev, char **envp, int num_envp,
+			       char *buffer, int buffer_size);
+
+#else
+
+static inline int power_supply_create_attrs(struct power_supply *psy)
+{ return 0; }
+static inline void power_supply_remove_attrs(struct power_supply *psy) {}
+#define power_supply_uevent NULL
+
+#endif /* CONFIG_SYSFS */
+
+#ifdef CONFIG_LEDS_TRIGGERS
+
+extern void power_supply_update_leds(struct power_supply *psy);
+extern int power_supply_create_triggers(struct power_supply *psy);
+extern void power_supply_remove_triggers(struct power_supply *psy);
+
+#else
+
+static inline void power_supply_update_leds(struct power_supply *psy) {}
+static inline int power_supply_create_triggers(struct power_supply *psy)
+{ return 0; }
+static inline void power_supply_remove_triggers(struct power_supply *psy) {}
+
+#endif /* CONFIG_LEDS_TRIGGERS */

drivers/power/power_supply_core.c

+/*
+ *  Universal power supply monitor class
+ *
+ *  Copyright © 2007  Anton Vorontsov <cbou@mail.ru>
+ *  Copyright © 2004  Szabolcs Gyurko
+ *  Copyright © 2003  Ian Molton <spyro@f2s.com>
+ *
+ *  Modified: 2004, Oct     Szabolcs Gyurko
+ *
+ *  You may use this code as per GPL version 2
+ */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/init.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/power_supply.h>
+#include "power_supply.h"
+
+struct class *power_supply_class;
+
+static void power_supply_changed_work(struct work_struct *work)
+{
+	struct power_supply *psy = container_of(work, struct power_supply,
+						changed_work);
+	int i;
+
+	dev_dbg(psy->dev, "%s\n", __FUNCTION__);
+
+	for (i = 0; i < psy->num_supplicants; i++) {
+		struct device *dev;
+
+		down(&power_supply_class->sem);
+		list_for_each_entry(dev, &power_supply_class->devices, node) {
+			struct power_supply *pst = dev_get_drvdata(dev);
+
+			if (!strcmp(psy->supplied_to[i], pst->name)) {
+				if (pst->external_power_changed)
+					pst->external_power_changed(pst);
+			}
+		}
+		up(&power_supply_class->sem);
+	}
+
+	power_supply_update_leds(psy);
+
+	kobject_uevent(&psy->dev->kobj, KOBJ_CHANGE);
+
+	return;
+}
+
+void power_supply_changed(struct power_supply *psy)
+{
+	dev_dbg(psy->dev, "%s\n", __FUNCTION__);
+
+	schedule_work(&psy->changed_work);
+
+	return;
+}
+
+int power_supply_am_i_supplied(struct power_supply *psy)
+{
+	union power_supply_propval ret = {0,};
+	struct device *dev;
+
+	down(&power_supply_class->sem);
+	list_for_each_entry(dev, &power_supply_class->devices, node) {
+		struct power_supply *epsy = dev_get_drvdata(dev);
+		int i;
+
+		for (i = 0; i < epsy->num_supplicants; i++) {
+			if (!strcmp(epsy->supplied_to[i], psy->name)) {
+				if (epsy->get_property(epsy,
+					  POWER_SUPPLY_PROP_ONLINE, &ret))
+					continue;
+				if (ret.intval)
+					goto out;
+			}
+		}
+	}
+out:
+	up(&power_supply_class->sem);
+
+	dev_dbg(psy->dev, "%s %d\n", __FUNCTION__, ret.intval);
+
+	return ret.intval;
+}
+
+int power_supply_register(struct device *parent, struct power_supply *psy)
+{
+	int rc = 0;
+
+	psy->dev = device_create(power_supply_class, parent, 0,
+				 "%s", psy->name);
+	if (IS_ERR(psy->dev)) {
+		rc = PTR_ERR(psy->dev);
+		goto dev_create_failed;
+	}
+
+	dev_set_drvdata(psy->dev, psy);
+
+	INIT_WORK(&psy->changed_work, power_supply_changed_work);
+
+	rc = power_supply_create_attrs(psy);
+	if (rc)
+		goto create_attrs_failed;
+
+	rc = power_supply_create_triggers(psy);
+	if (rc)
+		goto create_triggers_failed;
+
+	power_supply_changed(psy);
+
+	goto success;
+
+create_triggers_failed:
+	power_supply_remove_attrs(psy);
+create_attrs_failed:
+	device_unregister(psy->dev);
+dev_create_failed:
+success:
+	return rc;
+}
+
+void power_supply_unregister(struct power_supply *psy)
+{
+	flush_scheduled_work();
+	power_supply_remove_triggers(psy);
+	power_supply_remove_attrs(psy);
+	device_unregister(psy->dev);
+	return;
+}
+
+static int __init power_supply_class_init(void)
+{
+	power_supply_class = class_create(THIS_MODULE, "power_supply");
+
+	if (IS_ERR(power_supply_class))
+		return PTR_ERR(power_supply_class);
+
+	power_supply_class->dev_uevent = power_supply_uevent;
+
+	return 0;
+}
+
+static void __exit power_supply_class_exit(void)
+{
+	class_destroy(power_supply_class);
+	return;
+}
+
+EXPORT_SYMBOL_GPL(power_supply_changed);
+EXPORT_SYMBOL_GPL(power_supply_am_i_supplied);
+EXPORT_SYMBOL_GPL(power_supply_register);
+EXPORT_SYMBOL_GPL(power_supply_unregister);
+
+/* exported for the APM Power driver, APM emulation */
+EXPORT_SYMBOL_GPL(power_supply_class);
+
+subsys_initcall(power_supply_class_init);
+module_exit(power_supply_class_exit);
+
+MODULE_DESCRIPTION("Universal power supply monitor class");
+MODULE_AUTHOR("Ian Molton <spyro@f2s.com>, "
+	      "Szabolcs Gyurko, "
+	      "Anton Vorontsov <cbou@mail.ru>");
+MODULE_LICENSE("GPL");

drivers/power/power_supply_leds.c

+/*
+ *  LEDs triggers for power supply class
+ *
+ *  Copyright © 2007  Anton Vorontsov <cbou@mail.ru>
+ *  Copyright © 2004  Szabolcs Gyurko
+ *  Copyright © 2003  Ian Molton <spyro@f2s.com>
+ *
+ *  Modified: 2004, Oct     Szabolcs Gyurko
+ *
+ *  You may use this code as per GPL version 2
+ */
+
+#include <linux/power_supply.h>
+
+/* Battery specific LEDs triggers. */
+
+static void power_supply_update_bat_leds(struct power_supply *psy)
+{
+	union power_supply_propval status;
+
+	if (psy->get_property(psy, POWER_SUPPLY_PROP_STATUS, &status))
+		return;
+
+	dev_dbg(psy->dev, "%s %d\n", __FUNCTION__, status.intval);
+
+	switch (status.intval) {
+	case POWER_SUPPLY_STATUS_FULL:
+		led_trigger_event(psy->charging_full_trig, LED_FULL);
+		led_trigger_event(psy->charging_trig, LED_OFF);
+		led_trigger_event(psy->full_trig, LED_FULL);
+		break;
+	case POWER_SUPPLY_STATUS_CHARGING:
+		led_trigger_event(psy->charging_full_trig, LED_FULL);
+		led_trigger_event(psy->charging_trig, LED_FULL);
+		led_trigger_event(psy->full_trig, LED_OFF);
+		break;
+	default:
+		led_trigger_event(psy->charging_full_trig, LED_OFF);
+		led_trigger_event(psy->charging_trig, LED_OFF);
+		led_trigger_event(psy->full_trig, LED_OFF);
+		break;
+	}
+
+	return;
+}
+
+static int power_supply_create_bat_triggers(struct power_supply *psy)
+{
+	int rc = 0;
+
+	psy->charging_full_trig_name = kmalloc(strlen(psy->name) +
+				  sizeof("-charging-or-full"), GFP_KERNEL);
+	if (!psy->charging_full_trig_name)
+		goto charging_full_failed;
+
+	psy->charging_trig_name = kmalloc(strlen(psy->name) +
+					  sizeof("-charging"), GFP_KERNEL);
+	if (!psy->charging_trig_name)
+		goto charging_failed;
+
+	psy->full_trig_name = kmalloc(strlen(psy->name) +
+				      sizeof("-full"), GFP_KERNEL);
+	if (!psy->full_trig_name)
+		goto full_failed;
+
+	strcpy(psy->charging_full_trig_name, psy->name);
+	strcat(psy->charging_full_trig_name, "-charging-or-full");
+	strcpy(psy->charging_trig_name, psy->name);
+	strcat(psy->charging_trig_name, "-charging");
+	strcpy(psy->full_trig_name, psy->name);
+	strcat(psy->full_trig_name, "-full");
+
+	led_trigger_register_simple(psy->charging_full_trig_name,
+				    &psy->charging_full_trig);
+	led_trigger_register_simple(psy->charging_trig_name,
+				    &psy->charging_trig);
+	led_trigger_register_simple(psy->full_trig_name,
+				    &psy->full_trig);
+
+	goto success;
+
+full_failed:
+	kfree(psy->charging_trig_name);
+charging_failed:
+	kfree(psy->charging_full_trig_name);
+charging_full_failed:
+	rc = -ENOMEM;
+success:
+	return rc;
+}
+
+static void power_supply_remove_bat_triggers(struct power_supply *psy)
+{
+	led_trigger_unregister_simple(psy->charging_full_trig);
+	led_trigger_unregister_simple(psy->charging_trig);
+	led_trigger_unregister_simple(psy->full_trig);
+	kfree(psy->full_trig_name);
+	kfree(psy->charging_trig_name);
+	kfree(psy->charging_full_trig_name);
+	return;
+}
+
+/* Generated power specific LEDs triggers. */
+
+static void power_supply_update_gen_leds(struct power_supply *psy)
+{
+	union power_supply_propval online;
+
+	if (psy->get_property(psy, POWER_SUPPLY_PROP_ONLINE, &online))
+		return;
+
+	dev_dbg(psy->dev, "%s %d\n", __FUNCTION__, online.intval);
+
+	if (online.intval)
+		led_trigger_event(psy->online_trig, LED_FULL);
+	else
+		led_trigger_event(psy->online_trig, LED_OFF);
+
+	return;
+}
+
+static int power_supply_create_gen_triggers(struct power_supply *psy)
+{
+	int rc = 0;
+
+	psy->online_trig_name = kmalloc(strlen(psy->name) + sizeof("-online"),
+					GFP_KERNEL);
+	if (!psy->online_trig_name)
+		goto online_failed;
+
+	strcpy(psy->online_trig_name, psy->name);
+	strcat(psy->online_trig_name, "-online");
+
+	led_trigger_register_simple(psy->online_trig_name, &psy->online_trig);
+
+	goto success;
+
+online_failed:
+	rc = -ENOMEM;
+success:
+	return rc;
+}
+
+static void power_supply_remove_gen_triggers(struct power_supply *psy)
+{
+	led_trigger_unregister_simple(psy->online_trig);
+	kfree(psy->online_trig_name);
+	return;
+}
+
+/* Choice what triggers to create&update. */
+
+void power_supply_update_leds(struct power_supply *psy)
+{
+	if (psy->type == POWER_SUPPLY_TYPE_BATTERY)
+		power_supply_update_bat_leds(psy);
+	else
+		power_supply_update_gen_leds(psy);
+	return;
+}
+
+int power_supply_create_triggers(struct power_supply *psy)
+{
+	if (psy->type == POWER_SUPPLY_TYPE_BATTERY)
+		return power_supply_create_bat_triggers(psy);
+	return power_supply_create_gen_triggers(psy);
+}
+
+void power_supply_remove_triggers(struct power_supply *psy)
+{
+	if (psy->type == POWER_SUPPLY_TYPE_BATTERY)
+		power_supply_remove_bat_triggers(psy);
+	else
+		power_supply_remove_gen_triggers(psy);
+	return;
+}

drivers/power/power_supply_sysfs.c

+/*
+ *  Sysfs interface for the universal power supply monitor class
+ *
+ *  Copyright © 2007  David Woodhouse <dwmw2@infradead.org>
+ *  Copyright © 2007  Anton Vorontsov <cbou@mail.ru>
+ *  Copyright © 2004  Szabolcs Gyurko
+ *  Copyright © 2003  Ian Molton <spyro@f2s.com>
+ *
+ *  Modified: 2004, Oct     Szabolcs Gyurko
+ *
+ *  You may use this code as per GPL version 2
+ */
+
+#include <linux/ctype.h>
+#include <linux/power_supply.h>
+
+/*
+ * This is because the name "current" breaks the device attr macro.
+ * The "current" word resolves to "(get_current())" so instead of
+ * "current" "(get_current())" appears in the sysfs.
+ *
+ * The source of this definition is the device.h which calls __ATTR
+ * macro in sysfs.h which calls the __stringify macro.
+ *
+ * Only modification that the name is not tried to be resolved
+ * (as a macro let's say).
+ */
+
+#define POWER_SUPPLY_ATTR(_name)					\
+{									\
+	.attr = { .name = #_name, .mode = 0444, .owner = THIS_MODULE },	\
+	.show = power_supply_show_property,				\
+	.store = NULL,							\
+}
+
+static struct device_attribute power_supply_attrs[];
+
+static ssize_t power_supply_show_property(struct device *dev,
+					  struct device_attribute *attr,
+					  char *buf) {
+	static char *status_text[] = {
+		"Unknown", "Charging", "Discharging", "Not charging", "Full"
+	};
+	static char *health_text[] = {
+		"Unknown", "Good", "Overheat", "Dead", "Over voltage",
+		"Unspecified failure"
+	};
+	static char *technology_text[] = {
+		"Unknown", "NiMH", "Li-ion", "Li-poly", "LiFe", "NiCd"
+	};
+	static char *capacity_level_text[] = {
+		"Unknown", "Critical", "Low", "Normal", "High", "Full"
+	};
+	ssize_t ret;
+	struct power_supply *psy = dev_get_drvdata(dev);
+	const ptrdiff_t off = attr - power_supply_attrs;
+	union power_supply_propval value;
+
+	ret = psy->get_property(psy, off, &value);
+
+	if (ret < 0) {
+		if (ret != -ENODEV)
+			dev_err(dev, "driver failed to report `%s' property\n",
+				attr->attr.name);
+		return ret;
+	}
+
+	if (off == POWER_SUPPLY_PROP_STATUS)
+		return sprintf(buf, "%s\n", status_text[value.intval]);
+	else if (off == POWER_SUPPLY_PROP_HEALTH)
+		return sprintf(buf, "%s\n", health_text[value.intval]);
+	else if (off == POWER_SUPPLY_PROP_TECHNOLOGY)
+		return sprintf(buf, "%s\n", technology_text[value.intval]);
+	else if (off == POWER_SUPPLY_PROP_CAPACITY_LEVEL)
+		return sprintf(buf, "%s\n",
+			       capacity_level_text[value.intval]);
+	else if (off >= POWER_SUPPLY_PROP_MODEL_NAME)
+		return sprintf(buf, "%s\n", value.strval);
+
+	return sprintf(buf, "%d\n", value.intval);
+}
+
+/* Must be in the same order as POWER_SUPPLY_PROP_* */
+static struct device_attribute power_supply_attrs[] = {
+	/* Properties of type `int' */
+	POWER_SUPPLY_ATTR(status),
+	POWER_SUPPLY_ATTR(health),
+	POWER_SUPPLY_ATTR(present),
+	POWER_SUPPLY_ATTR(online),
+	POWER_SUPPLY_ATTR(technology),
+	POWER_SUPPLY_ATTR(voltage_max_design),
+	POWER_SUPPLY_ATTR(voltage_min_design),
+	POWER_SUPPLY_ATTR(voltage_now),
+	POWER_SUPPLY_ATTR(voltage_avg),
+	POWER_SUPPLY_ATTR(current_now),
+	POWER_SUPPLY_ATTR(current_avg),
+	POWER_SUPPLY_ATTR(charge_full_design),
+	POWER_SUPPLY_ATTR(charge_empty_design),
+	POWER_SUPPLY_ATTR(charge_full),
+	POWER_SUPPLY_ATTR(charge_empty),
+	POWER_SUPPLY_ATTR(charge_now),
+	POWER_SUPPLY_ATTR(charge_avg),
+	POWER_SUPPLY_ATTR(energy_full_design),
+	POWER_SUPPLY_ATTR(energy_empty_design),
+	POWER_SUPPLY_ATTR(energy_full),
+	POWER_SUPPLY_ATTR(energy_empty),
+	POWER_SUPPLY_ATTR(energy_now),
+	POWER_SUPPLY_ATTR(energy_avg),
+	POWER_SUPPLY_ATTR(capacity),
+	POWER_SUPPLY_ATTR(capacity_level),
+	POWER_SUPPLY_ATTR(temp),
+	POWER_SUPPLY_ATTR(temp_ambient),
+	POWER_SUPPLY_ATTR(time_to_empty_now),
+	POWER_SUPPLY_ATTR(time_to_empty_avg),
+	POWER_SUPPLY_ATTR(time_to_full_now),
+	POWER_SUPPLY_ATTR(time_to_full_avg),
+	/* Properties of type `const char *' */
+	POWER_SUPPLY_ATTR(model_name),
+	POWER_SUPPLY_ATTR(manufacturer),
+};
+
+static ssize_t power_supply_show_static_attrs(struct device *dev,
+					      struct device_attribute *attr,
+					      char *buf) {
+	static char *type_text[] = { "Battery", "UPS", "Mains", "USB" };
+	struct power_supply *psy = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%s\n", type_text[psy->type]);
+}
+
+static struct device_attribute power_supply_static_attrs[] = {
+	__ATTR(type, 0444, power_supply_show_static_attrs, NULL),
+};
+
+int power_supply_create_attrs(struct power_supply *psy)
+{
+	int rc = 0;
+	int i, j;
+
+	for (i = 0; i < ARRAY_SIZE(power_supply_static_attrs); i++) {
+		rc = device_create_file(psy->dev,
+			    &power_supply_static_attrs[i]);
+		if (rc)
+			goto statics_failed;
+	}
+
+	for (j = 0; j < psy->num_properties; j++) {
+		rc = device_create_file(psy->dev,
+			    &power_supply_attrs[psy->properties[j]]);
+		if (rc)
+			goto dynamics_failed;
+	}
+
+	goto succeed;
+
+dynamics_failed:
+	while (j--)
+		device_remove_file(psy->dev,
+			   &power_supply_attrs[psy->properties[j]]);
+statics_failed:
+	while (i--)
+		device_remove_file(psy->dev,
+			   &power_supply_static_attrs[psy->properties[i]]);
+succeed:
+	return rc;
+}
+
+void power_supply_remove_attrs(struct power_supply *psy)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(power_supply_static_attrs); i++)
+		device_remove_file(psy->dev,
+			    &power_supply_static_attrs[i]);
+
+	for (i = 0; i < psy->num_properties; i++)
+		device_remove_file(psy->dev,
+			    &power_supply_attrs[psy->properties[i]]);
+
+	return;
+}
+
+static char *kstruprdup(const char *str, gfp_t gfp)
+{
+	char *ret, *ustr;
+
+	ustr = ret = kmalloc(strlen(str) + 1, gfp);
+
+	if (!ret)
+		return NULL;
+
+	while (*str)
+		*ustr++ = toupper(*str++);
+
+	*ustr = 0;
+
+	return ret;
+}
+
+int power_supply_uevent(struct device *dev, char **envp, int num_envp,
+			char *buffer, int buffer_size)
+{
+	struct power_supply *psy = dev_get_drvdata(dev);
+	int i = 0, length = 0, ret = 0, j;
+	char *prop_buf;
+	char *attrname;
+
+	dev_dbg(dev, "uevent\n");
+
+	if (!psy) {
+		dev_dbg(dev, "No power supply yet\n");
+		return ret;
+	}
+
+	dev_dbg(dev, "POWER_SUPPLY_NAME=%s\n", psy->name);
+
+	ret = add_uevent_var(envp, num_envp, &i, buffer, buffer_size,
+			     &length, "POWER_SUPPLY_NAME=%s", psy->name);
+	if (ret)
+		return ret;
+
+	prop_buf = (char *)get_zeroed_page(GFP_KERNEL);
+	if (!prop_buf)
+		return -ENOMEM;
+
+	for (j = 0; j < ARRAY_SIZE(power_supply_static_attrs); j++) {
+		struct device_attribute *attr;
+		char *line;
+
+		attr = &power_supply_static_attrs[j];
+
+		ret = power_supply_show_static_attrs(dev, attr, prop_buf);
+		if (ret < 0)
+			goto out;
+
+		line = strchr(prop_buf, '\n');
+		if (line)
+			*line = 0;
+
+		attrname = kstruprdup(attr->attr.name, GFP_KERNEL);
+		if (!attrname) {
+			ret = -ENOMEM;
+			goto out;
+		}
+
+		dev_dbg(dev, "Static prop %s=%s\n", attrname, prop_buf);
+
+		ret = add_uevent_var(envp, num_envp, &i, buffer, buffer_size,
+				     &length, "POWER_SUPPLY_%s=%s",
+				     attrname, prop_buf);
+		kfree(attrname);
+		if (ret)
+			goto out;
+	}
+
+	dev_dbg(dev, "%zd dynamic props\n", psy->num_properties);
+
+	for (j = 0; j < psy->num_properties; j++) {
+		struct device_attribute *attr;
+		char *line;
+
+		attr = &power_supply_attrs[psy->properties[j]];
+
+		ret = power_supply_show_property(dev, attr, prop_buf);
+		if (ret == -ENODEV) {
+			/* When a battery is absent, we expect -ENODEV. Don't abort;
+			   send the uevent with at least the the PRESENT=0 property */
+			ret = 0;
+			continue;
+		}
+
+		if (ret < 0)
+			goto out;
+
+		line = strchr(prop_buf, '\n');
+		if (line)
+			*line = 0;
+
+		attrname = kstruprdup(attr->attr.name, GFP_KERNEL);
+		if (!attrname) {
+			ret = -ENOMEM;
+			goto out;
+		}
+
+		dev_dbg(dev, "prop %s=%s\n", attrname, prop_buf);
+
+		ret = add_uevent_var(envp, num_envp, &i, buffer, buffer_size,
+				     &length, "POWER_SUPPLY_%s=%s",
+				     attrname, prop_buf);
+		kfree(attrname);
+		if (ret)
+			goto out;
+	}
+
+out:
+	free_page((unsigned long)prop_buf);
+
+	return ret;
+}

include/linux/power_supply.h

+/*
+ *  Universal power supply monitor class
+ *
+ *  Copyright © 2007  Anton Vorontsov <cbou@mail.ru>
+ *  Copyright © 2004  Szabolcs Gyurko
+ *  Copyright © 2003  Ian Molton <spyro@f2s.com>
+ *
+ *  Modified: 2004, Oct     Szabolcs Gyurko
+ *
+ *  You may use this code as per GPL version 2
+ */
+
+#ifndef __LINUX_POWER_SUPPLY_H__
+#define __LINUX_POWER_SUPPLY_H__
+
+#include <linux/device.h>
+#include <linux/workqueue.h>
+#include <linux/leds.h>
+
+/*
+ * All voltages, currents, charges, energies, time and temperatures in uV,
+ * µA, µAh, µWh, seconds and tenths of degree Celsius unless otherwise
+ * stated. It's driver's job to convert its raw values to units in which
+ * this class operates.
+ */
+
+/*
+ * For systems where the charger determines the maximum battery capacity
+ * the min and max fields should be used to present these values to user
+ * space. Unused/unknown fields will not appear in sysfs.
+ */
+
+enum {
+	POWER_SUPPLY_STATUS_UNKNOWN = 0,
+	POWER_SUPPLY_STATUS_CHARGING,
+	POWER_SUPPLY_STATUS_DISCHARGING,
+	POWER_SUPPLY_STATUS_NOT_CHARGING,
+	POWER_SUPPLY_STATUS_FULL,
+};
+
+enum {
+	POWER_SUPPLY_HEALTH_UNKNOWN = 0,
+	POWER_SUPPLY_HEALTH_GOOD,
+	POWER_SUPPLY_HEALTH_OVERHEAT,
+	POWER_SUPPLY_HEALTH_DEAD,
+	POWER_SUPPLY_HEALTH_OVERVOLTAGE,
+	POWER_SUPPLY_HEALTH_UNSPEC_FAILURE,
+};
+
+enum {
+	POWER_SUPPLY_TECHNOLOGY_UNKNOWN = 0,
+	POWER_SUPPLY_TECHNOLOGY_NiMH,
+	POWER_SUPPLY_TECHNOLOGY_LION,
+	POWER_SUPPLY_TECHNOLOGY_LIPO,
+	POWER_SUPPLY_TECHNOLOGY_LiFe,
+	POWER_SUPPLY_TECHNOLOGY_NiCd,
+};
+
+enum {
+	POWER_SUPPLY_CAPACITY_LEVEL_UNKNOWN = 0,
+	POWER_SUPPLY_CAPACITY_LEVEL_CRITICAL,
+	POWER_SUPPLY_CAPACITY_LEVEL_LOW,
+	POWER_SUPPLY_CAPACITY_LEVEL_NORMAL,
+	POWER_SUPPLY_CAPACITY_LEVEL_HIGH,
+	POWER_SUPPLY_CAPACITY_LEVEL_FULL,
+};
+
+enum power_supply_property {
+	/* Properties of type `int' */
+	POWER_SUPPLY_PROP_STATUS = 0,
+	POWER_SUPPLY_PROP_HEALTH,
+	POWER_SUPPLY_PROP_PRESENT,
+	POWER_SUPPLY_PROP_ONLINE,
+	POWER_SUPPLY_PROP_TECHNOLOGY,
+	POWER_SUPPLY_PROP_VOLTAGE_MAX_DESIGN,
+	POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN,
+	POWER_SUPPLY_PROP_VOLTAGE_NOW,
+	POWER_SUPPLY_PROP_VOLTAGE_AVG,
+	POWER_SUPPLY_PROP_CURRENT_NOW,
+	POWER_SUPPLY_PROP_CURRENT_AVG,
+	POWER_SUPPLY_PROP_CHARGE_FULL_DESIGN,
+	POWER_SUPPLY_PROP_CHARGE_EMPTY_DESIGN,
+	POWER_SUPPLY_PROP_CHARGE_FULL,
+	POWER_SUPPLY_PROP_CHARGE_EMPTY,
+	POWER_SUPPLY_PROP_CHARGE_NOW,
+	POWER_SUPPLY_PROP_CHARGE_AVG,
+	POWER_SUPPLY_PROP_ENERGY_FULL_DESIGN,
+	POWER_SUPPLY_PROP_ENERGY_EMPTY_DESIGN,
+	POWER_SUPPLY_PROP_ENERGY_FULL,
+	POWER_SUPPLY_PROP_ENERGY_EMPTY,
+	POWER_SUPPLY_PROP_ENERGY_NOW,
+	POWER_SUPPLY_PROP_ENERGY_AVG,
+	POWER_SUPPLY_PROP_CAPACITY, /* in percents! */
+	POWER_SUPPLY_PROP_CAPACITY_LEVEL,
+	POWER_SUPPLY_PROP_TEMP,
+	POWER_SUPPLY_PROP_TEMP_AMBIENT,
+	POWER_SUPPLY_PROP_TIME_TO_EMPTY_NOW,
+	POWER_SUPPLY_PROP_TIME_TO_EMPTY_AVG,
+	POWER_SUPPLY_PROP_TIME_TO_FULL_NOW,
+	POWER_SUPPLY_PROP_TIME_TO_FULL_AVG,
+	/* Properties of type `const char *' */
+	POWER_SUPPLY_PROP_MODEL_NAME,
+	POWER_SUPPLY_PROP_MANUFACTURER,
+};
+
+enum power_supply_type {
+	POWER_SUPPLY_TYPE_BATTERY = 0,
+	POWER_SUPPLY_TYPE_UPS,
+	POWER_SUPPLY_TYPE_MAINS,
+	POWER_SUPPLY_TYPE_USB,
+};
+
+union power_supply_propval {
+	int intval;
+	const char *strval;
+};
+
+struct power_supply {
+	const char *name;
+	enum power_supply_type type;
+	enum power_supply_property *properties;
+	size_t num_properties;
+
+	char **supplied_to;
+	size_t num_supplicants;
+
+	int (*get_property)(struct power_supply *psy,
+			    enum power_supply_property psp,
+			    union power_supply_propval *val);
+	void (*external_power_changed)(struct power_supply *psy);
+
+	/* For APM emulation, think legacy userspace. */
+	int use_for_apm;
+
+	/* private */
+	struct device *dev;
+	struct work_struct changed_work;
+
+#ifdef CONFIG_LEDS_TRIGGERS
+	struct led_trigger *charging_full_trig;
+	char *charging_full_trig_name;
+	struct led_trigger *charging_trig;
+	char *charging_trig_name;
+	struct led_trigger *full_trig;
+	char *full_trig_name;
+	struct led_trigger *online_trig;
+	char *online_trig_name;
+#endif
+};
+
+/*
+ * This is recommended structure to specify static power supply parameters.
+ * Generic one, parametrizable for different power supplies. Power supply
+ * class itself does not use it, but that's what implementing most platform
+ * drivers, should try reuse for consistency.
+ */
+
+struct power_supply_info {
+	const char *name;
+	int technology;
+	int voltage_max_design;
+	int voltage_min_design;
+	int charge_full_design;
+	int charge_empty_design;
+	int energy_full_design;
+	int energy_empty_design;
+	int use_for_apm;
+};
+
+extern void power_supply_changed(struct power_supply *psy);
+extern int power_supply_am_i_supplied(struct power_supply *psy);
+
+extern int power_supply_register(struct device *parent,
+				 struct power_supply *psy);
+extern void power_supply_unregister(struct power_supply *psy);
+
+/* For APM emulation, think legacy userspace. */
+extern struct class *power_supply_class;
+
+#endif /* __LINUX_POWER_SUPPLY_H__ */