--- /dev/null
+========================
+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/supply/ds2760_battery.c and drivers/power/supply/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.
+
+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.
+
+VOLTAGE_BOOT
+ Reports the voltage measured during boot
+
+CURRENT_BOOT
+ Reports the current measured during boot
+
+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.
+
+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.
+
+PRECHARGE_CURRENT
+ the maximum charge current during precharge phase of charge cycle
+ (typically 20% of battery capacity).
+
+CHARGE_TERM_CURRENT
+ Charge termination current. The charge cycle terminates when battery
+ voltage is above recharge threshold, and charge current is below
+ this setting (typically 10% of battery capacity).
+
+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.
+
+INPUT_CURRENT_LIMIT
+ input current limit programmed by charger. Indicates
+ the current drawn from a charging source.
++INPUT_VOLTAGE_LIMIT
++ input voltage limit programmed by charger. Indicates
++ the voltage limit from a charging source.
++INPUT_POWER_LIMIT
++ input power limit programmed by charger. Indicates
++ the power limit from a charging source.
+
+CHARGE_CONTROL_LIMIT
+ current charge control limit setting
+CHARGE_CONTROL_LIMIT_MAX
+ maximum charge control limit setting
+
+CALIBRATE
+ battery or coulomb counter calibration status
+
+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 POWER_SUPPLY_CAPACITY_LEVEL_*.
+
+TEMP
+ temperature of the power supply.
+TEMP_ALERT_MIN
+ minimum battery temperature alert.
+TEMP_ALERT_MAX
+ maximum battery temperature alert.
+TEMP_AMBIENT
+ ambient temperature.
+TEMP_AMBIENT_ALERT_MIN
+ minimum ambient temperature alert.
+TEMP_AMBIENT_ALERT_MAX
+ maximum ambient temperature alert.
+TEMP_MIN
+ minimum operatable temperature
+TEMP_MAX
+ maximum operatable 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.
+
+
+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?
+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.
projects / users / willy / pagecache.git / commitdiff