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Subject[PATCH 09/13] regulator: documentation - overview
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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>
---
Documentation/power/regulator/overview.txt | 171 ++++++++++++++++++++++++++++
1 files changed, 171 insertions(+), 0 deletions(-)
create mode 100644 Documentation/power/regulator/overview.txt
diff --git a/Documentation/power/regulator/overview.txt b/Documentation/power/regulator/overview.txt
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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
--
1.5.4.3



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