172 lines
6.7 KiB
Plaintext
172 lines
6.7 KiB
Plaintext
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Linux voltage and current regulator framework
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=============================================
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About
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=====
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This framework is designed to provide a standard kernel interface to control
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voltage and current regulators.
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The intention is to allow systems to dynamically control regulator power output
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in order to save power and prolong battery life. This applies to both voltage
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regulators (where voltage output is controllable) and current sinks (where
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current limit is controllable).
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(C) 2008 Wolfson Microelectronics PLC.
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Author: Liam Girdwood <lrg@slimlogic.co.uk>
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Nomenclature
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============
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Some terms used in this document:-
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o Regulator - Electronic device that supplies power to other devices.
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Most regulators can enable and disable their output whilst
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some can control their output voltage and or current.
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Input Voltage -> Regulator -> Output Voltage
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o PMIC - Power Management IC. An IC that contains numerous regulators
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and often contains other subsystems.
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o Consumer - Electronic device that is supplied power by a regulator.
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Consumers can be classified into two types:-
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Static: consumer does not change its supply voltage or
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current limit. It only needs to enable or disable it's
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power supply. Its supply voltage is set by the hardware,
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bootloader, firmware or kernel board initialisation code.
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Dynamic: consumer needs to change it's supply voltage or
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current limit to meet operation demands.
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o Power Domain - Electronic circuit that is supplied its input power by the
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output power of a regulator, switch or by another power
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domain.
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The supply regulator may be behind a switch(s). i.e.
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Regulator -+-> Switch-1 -+-> Switch-2 --> [Consumer A]
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| +-> [Consumer B], [Consumer C]
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+-> [Consumer D], [Consumer E]
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That is one regulator and three power domains:
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Domain 1: Switch-1, Consumers D & E.
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Domain 2: Switch-2, Consumers B & C.
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Domain 3: Consumer A.
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and this represents a "supplies" relationship:
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Domain-1 --> Domain-2 --> Domain-3.
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A power domain may have regulators that are supplied power
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by other regulators. i.e.
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Regulator-1 -+-> Regulator-2 -+-> [Consumer A]
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+-> [Consumer B]
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This gives us two regulators and two power domains:
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Domain 1: Regulator-2, Consumer B.
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Domain 2: Consumer A.
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and a "supplies" relationship:
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Domain-1 --> Domain-2
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o Constraints - Constraints are used to define power levels for performance
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and hardware protection. Constraints exist at three levels:
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Regulator Level: This is defined by the regulator hardware
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operating parameters and is specified in the regulator
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datasheet. i.e.
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- voltage output is in the range 800mV -> 3500mV.
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- regulator current output limit is 20mA @ 5V but is
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10mA @ 10V.
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Power Domain Level: This is defined in software by kernel
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level board initialisation code. It is used to constrain a
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power domain to a particular power range. i.e.
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- Domain-1 voltage is 3300mV
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- Domain-2 voltage is 1400mV -> 1600mV
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- Domain-3 current limit is 0mA -> 20mA.
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Consumer Level: This is defined by consumer drivers
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dynamically setting voltage or current limit levels.
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e.g. a consumer backlight driver asks for a current increase
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from 5mA to 10mA to increase LCD illumination. This passes
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to through the levels as follows :-
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Consumer: need to increase LCD brightness. Lookup and
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request next current mA value in brightness table (the
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consumer driver could be used on several different
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personalities based upon the same reference device).
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Power Domain: is the new current limit within the domain
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operating limits for this domain and system state (e.g.
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battery power, USB power)
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Regulator Domains: is the new current limit within the
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regulator operating parameters for input/output voltage.
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If the regulator request passes all the constraint tests
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then the new regulator value is applied.
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Design
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======
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The framework is designed and targeted at SoC based devices but may also be
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relevant to non SoC devices and is split into the following four interfaces:-
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1. Consumer driver interface.
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This uses a similar API to the kernel clock interface in that consumer
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drivers can get and put a regulator (like they can with clocks atm) and
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get/set voltage, current limit, mode, enable and disable. This should
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allow consumers complete control over their supply voltage and current
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limit. This also compiles out if not in use so drivers can be reused in
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systems with no regulator based power control.
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See Documentation/power/regulator/consumer.txt
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2. Regulator driver interface.
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This allows regulator drivers to register their regulators and provide
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operations to the core. It also has a notifier call chain for propagating
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regulator events to clients.
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See Documentation/power/regulator/regulator.txt
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3. Machine interface.
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This interface is for machine specific code and allows the creation of
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voltage/current domains (with constraints) for each regulator. It can
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provide regulator constraints that will prevent device damage through
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overvoltage or over current caused by buggy client drivers. It also
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allows the creation of a regulator tree whereby some regulators are
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supplied by others (similar to a clock tree).
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See Documentation/power/regulator/machine.txt
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4. Userspace ABI.
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The framework also exports a lot of useful voltage/current/opmode data to
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userspace via sysfs. This could be used to help monitor device power
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consumption and status.
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See Documentation/ABI/testing/sysfs-class-regulator
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