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+Linux power supply class
+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
+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
+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
+See drivers/power/ds2760_battery.c and drivers/power/pda_power.c for the
+example how to declare and handle attributes.
+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. ~
+~ ~
+~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
+_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.
+CHARGE_TYPE - batteries can typically charge at different rates.
+This defines trickle and fast charges. For batteries that
+are already charged or discharging, 'n/a' can be displayed (or
+'unknown', if the status is not known).
+AUTHENTIC - indicates the power supply (battery or charger) connected
+to the platform is authentic(1) or non authentic(0).
+HEALTH - represents health of the battery, values corresponds to
+POWER_SUPPLY_HEALTH_*, defined in battery.h.
+VOLTAGE_OCV - open circuit voltage of the battery.
+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.
+VOLTAGE_MAX, VOLTAGE_MIN - same as _DESIGN voltage values except that
+these ones should be used if hardware could only guess (measure and
+retain) the thresholds of a given power supply.
+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.
+CHARGE_COUNTER - the current charge counter (in µAh). This could easily
+be negative; there is no empty or full value. It is only useful for
+relative, time-based measurements.
+CONSTANT_CHARGE_CURRENT - constant charge current programmed by charger.
+CONSTANT_CHARGE_CURRENT_MAX - maximum charge current supported by the
+power supply object.
+CONSTANT_CHARGE_VOLTAGE - constant charge voltage programmed by charger.
+CONSTANT_CHARGE_VOLTAGE_MAX - maximum charge voltage supported by the
+power supply object.
+CHARGE_CONTROL_LIMIT - current charge control limit setting
+CHARGE_CONTROL_LIMIT_MAX - maximum charge control limit setting
+ENERGY_FULL, ENERGY_EMPTY - same as above but for energy.
+CAPACITY - capacity in percents.
+CAPACITY_ALERT_MIN - minimum capacity alert value in percents.
+CAPACITY_ALERT_MAX - maximum capacity alert value in percents.
+CAPACITY_LEVEL - capacity level. This corresponds to
+TEMP - temperature of the power supply.
+TEMP_ALERT_MIN - minimum battery temperature alert value in milli centigrade.
+TEMP_ALERT_MAX - maximum battery temperature alert value in milli centigrade.
+TEMP_AMBIENT - ambient temperature.
+TEMP_AMBIENT_ALERT_MIN - minimum ambient temperature alert value in milli centigrade.
+TEMP_AMBIENT_ALERT_MAX - maximum ambient temperature alert value in milli centigrade.
+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
+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.
+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.