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<book id="regulator-api">
<bookinfo>
<title>Voltage and current regulator API</title>
<authorgroup>
<author>
<firstname>Liam</firstname>
<surname>Girdwood</surname>
<affiliation>
<address>
<email>lrg@slimlogic.co.uk</email>
</address>
</affiliation>
</author>
<author>
<firstname>Mark</firstname>
<surname>Brown</surname>
<affiliation>
<orgname>Wolfson Microelectronics</orgname>
<address>
<email>broonie@opensource.wolfsonmicro.com</email>
</address>
</affiliation>
</author>
</authorgroup>
<copyright>
<year>2007-2008</year>
<holder>Wolfson Microelectronics</holder>
</copyright>
<copyright>
<year>2008</year>
<holder>Liam Girdwood</holder>
</copyright>
<legalnotice>
<para>
This documentation is free software; you can redistribute
it and/or modify it under the terms of the GNU General Public
License version 2 as published by the Free Software Foundation.
</para>
<para>
This program is distributed in the hope that it will be
useful, but WITHOUT ANY WARRANTY; without even the implied
warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
See the GNU General Public License for more details.
</para>
<para>
You should have received a copy of the GNU General Public
License along with this program; if not, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
MA 02111-1307 USA
</para>
<para>
For more details see the file COPYING in the source
distribution of Linux.
</para>
</legalnotice>
</bookinfo>
<toc></toc>
<chapter id="intro">
<title>Introduction</title>
<para>
This framework is designed to provide a standard kernel
interface to control voltage and current regulators.
</para>
<para>
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).
</para>
<para>
Note that additional (and currently more complete) documentation
is available in the Linux kernel source under
<filename>Documentation/power/regulator</filename>.
</para>
<sect1 id="glossary">
<title>Glossary</title>
<para>
The regulator API uses a number of terms which may not be
familiar:
</para>
<glossary>
<glossentry>
<glossterm>Regulator</glossterm>
<glossdef>
<para>
Electronic device that supplies power to other devices. Most
regulators can enable and disable their output and some can also
control their output voltage or current.
</para>
</glossdef>
</glossentry>
<glossentry>
<glossterm>Consumer</glossterm>
<glossdef>
<para>
Electronic device which consumes power provided by a regulator.
These may either be static, requiring only a fixed supply, or
dynamic, requiring active management of the regulator at
runtime.
</para>
</glossdef>
</glossentry>
<glossentry>
<glossterm>Power Domain</glossterm>
<glossdef>
<para>
The electronic circuit supplied by a given regulator, including
the regulator and all consumer devices. The configuration of
the regulator is shared between all the components in the
circuit.
</para>
</glossdef>
</glossentry>
<glossentry>
<glossterm>Power Management Integrated Circuit</glossterm>
<acronym>PMIC</acronym>
<glossdef>
<para>
An IC which contains numerous regulators and often also other
subsystems. In an embedded system the primary PMIC is often
equivalent to a combination of the PSU and southbridge in a
desktop system.
</para>
</glossdef>
</glossentry>
</glossary>
</sect1>
</chapter>
<chapter id="consumer">
<title>Consumer driver interface</title>
<para>
This offers a similar API to the kernel clock framework.
Consumer drivers use <link
linkend='API-regulator-get'>get</link> and <link
linkend='API-regulator-put'>put</link> operations to acquire and
release regulators. Functions are
provided to <link linkend='API-regulator-enable'>enable</link>
and <link linkend='API-regulator-disable'>disable</link> the
regulator and to get and set the runtime parameters of the
regulator.
</para>
<para>
When requesting regulators consumers use symbolic names for their
supplies, such as "Vcc", which are mapped into actual regulator
devices by the machine interface.
</para>
<para>
A stub version of this API is provided when the regulator
framework is not in use in order to minimise the need to use
ifdefs.
</para>
<sect1 id="consumer-enable">
<title>Enabling and disabling</title>
<para>
The regulator API provides reference counted enabling and
disabling of regulators. Consumer devices use the <function><link
linkend='API-regulator-enable'>regulator_enable</link></function>
and <function><link
linkend='API-regulator-disable'>regulator_disable</link>
</function> functions to enable and disable regulators. Calls
to the two functions must be balanced.
</para>
<para>
Note that since multiple consumers may be using a regulator and
machine constraints may not allow the regulator to be disabled
there is no guarantee that calling
<function>regulator_disable</function> will actually cause the
supply provided by the regulator to be disabled. Consumer
drivers should assume that the regulator may be enabled at all
times.
</para>
</sect1>
<sect1 id="consumer-config">
<title>Configuration</title>
<para>
Some consumer devices may need to be able to dynamically
configure their supplies. For example, MMC drivers may need to
select the correct operating voltage for their cards. This may
be done while the regulator is enabled or disabled.
</para>
<para>
The <function><link
linkend='API-regulator-set-voltage'>regulator_set_voltage</link>
</function> and <function><link
linkend='API-regulator-set-current-limit'
>regulator_set_current_limit</link>
</function> functions provide the primary interface for this.
Both take ranges of voltages and currents, supporting drivers
that do not require a specific value (eg, CPU frequency scaling
normally permits the CPU to use a wider range of supply
voltages at lower frequencies but does not require that the
supply voltage be lowered). Where an exact value is required
both minimum and maximum values should be identical.
</para>
</sect1>
<sect1 id="consumer-callback">
<title>Callbacks</title>
<para>
Callbacks may also be <link
linkend='API-regulator-register-notifier'>registered</link>
for events such as regulation failures.
</para>
</sect1>
</chapter>
<chapter id="driver">
<title>Regulator driver interface</title>
<para>
Drivers for regulator chips <link
linkend='API-regulator-register'>register</link> the regulators
with the regulator core, providing operations structures to the
core. A <link
linkend='API-regulator-notifier-call-chain'>notifier</link> interface
allows error conditions to be reported to the core.
</para>
<para>
Registration should be triggered by explicit setup done by the
platform, supplying a <link
linkend='API-struct-regulator-init-data'>struct
regulator_init_data</link> for the regulator containing
<link linkend='machine-constraint'>constraint</link> and
<link linkend='machine-supply'>supply</link> information.
</para>
</chapter>
<chapter id="machine">
<title>Machine interface</title>
<para>
This interface provides a way to define how regulators are
connected to consumers on a given system and what the valid
operating parameters are for the system.
</para>
<sect1 id="machine-supply">
<title>Supplies</title>
<para>
Regulator supplies are specified using <link
linkend='API-struct-regulator-consumer-supply'>struct
regulator_consumer_supply</link>. This is done at
<link linkend='driver'>driver registration
time</link> as part of the machine constraints.
</para>
</sect1>
<sect1 id="machine-constraint">
<title>Constraints</title>
<para>
As well as defining the connections the machine interface
also provides constraints defining the operations that
clients are allowed to perform and the parameters that may be
set. This is required since generally regulator devices will
offer more flexibility than it is safe to use on a given
system, for example supporting higher supply voltages than the
consumers are rated for.
</para>
<para>
This is done at <link linkend='driver'>driver
registration time</link> by providing a <link
linkend='API-struct-regulation-constraints'>struct
regulation_constraints</link>.
</para>
<para>
The constraints may also specify an initial configuration for the
regulator in the constraints, which is particularly useful for
use with static consumers.
</para>
</sect1>
</chapter>
<chapter id="api">
<title>API reference</title>
<para>
Due to limitations of the kernel documentation framework and the
existing layout of the source code the entire regulator API is
documented here.
</para>
!Iinclude/linux/regulator/consumer.h
!Iinclude/linux/regulator/machine.h
!Iinclude/linux/regulator/driver.h
!Edrivers/regulator/core.c
</chapter>
</book>