mirror of
https://github.com/torvalds/linux.git
synced 2024-11-21 19:41:42 +00:00
151f4e2bdc
Convert the PM documents to ReST, in order to allow them to build with Sphinx. The conversion is actually: - add blank lines and indentation in order to identify paragraphs; - fix tables markups; - add some lists markups; - mark literal blocks; - adjust title markups. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Acked-by: Mark Brown <broonie@kernel.org> Acked-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
179 lines
6.9 KiB
ReStructuredText
179 lines
6.9 KiB
ReStructuredText
=============================================
|
|
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:
|
|
|
|
- Regulator
|
|
- Electronic device that supplies power to other devices.
|
|
Most regulators can enable and disable their output while
|
|
some can control their output voltage and or current.
|
|
|
|
Input Voltage -> Regulator -> Output Voltage
|
|
|
|
|
|
- PMIC
|
|
- Power Management IC. An IC that contains numerous
|
|
regulators and often contains other subsystems.
|
|
|
|
|
|
- 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.
|
|
|
|
|
|
- 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
|
|
|
|
|
|
- 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.rst
|
|
|
|
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.rst
|
|
|
|
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.rst
|
|
|
|
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
|