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