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regulator: documentation - overview 

This adds overview documentation describing the regulator framework and
nomenclature used in the interface specific documentation and code.

Signed-off-by: Liam Girdwood <lg@opensource.wolfsonmicro.com>
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Liam Girdwood 2008-04-30 17:16:51 +01:00
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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 <lg@opensource.wolfsonmicro.com>
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 susbsystems.
o Consumer - Electronic device that is supplied power by a regulator.
Consumers can be classified into two types:-
Static: consumer does not change it's supply voltage or
current limit. It only needs to enable or disable it's
power supply. It's supply voltage is set by the hardware,
bootloader, firmware or kernel board initialisation code.
Dynamic: consumer needs to change it's supply voltage or
current limit to meet operation demands.
o Power Domain - Electronic circuit that is supplied it's 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/ouput 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 over current 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/regulator-sysfs.txt