summaryrefslogtreecommitdiffstats
path: root/Documentation/power/power_supply_class.txt
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/power/power_supply_class.txt')
-rw-r--r--Documentation/power/power_supply_class.txt182
1 files changed, 0 insertions, 182 deletions
diff --git a/Documentation/power/power_supply_class.txt b/Documentation/power/power_supply_class.txt
deleted file mode 100644
index 211831d..0000000
--- a/Documentation/power/power_supply_class.txt
+++ /dev/null
@@ -1,182 +0,0 @@
-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.
-
-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).
-
-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.
-
-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.