305 lines
9.8 KiB
Cheetah
305 lines
9.8 KiB
Cheetah
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
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<book id="regulator-api">
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<bookinfo>
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<title>Voltage and current regulator API</title>
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<authorgroup>
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<author>
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<firstname>Liam</firstname>
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<surname>Girdwood</surname>
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<affiliation>
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<address>
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<email>lrg@slimlogic.co.uk</email>
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</address>
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</affiliation>
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</author>
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<author>
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<firstname>Mark</firstname>
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<surname>Brown</surname>
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<affiliation>
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<orgname>Wolfson Microelectronics</orgname>
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<address>
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<email>broonie@opensource.wolfsonmicro.com</email>
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</address>
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</affiliation>
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</author>
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</authorgroup>
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<copyright>
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<year>2007-2008</year>
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<holder>Wolfson Microelectronics</holder>
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</copyright>
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<copyright>
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<year>2008</year>
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<holder>Liam Girdwood</holder>
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</copyright>
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<legalnotice>
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<para>
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This documentation is free software; you can redistribute
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it and/or modify it under the terms of the GNU General Public
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License version 2 as published by the Free Software Foundation.
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</para>
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<para>
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This program is distributed in the hope that it will be
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useful, but WITHOUT ANY WARRANTY; without even the implied
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warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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See the GNU General Public License for more details.
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</para>
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<para>
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You should have received a copy of the GNU General Public
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License along with this program; if not, write to the Free
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Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
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MA 02111-1307 USA
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</para>
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<para>
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For more details see the file COPYING in the source
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distribution of Linux.
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</para>
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</legalnotice>
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</bookinfo>
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<toc></toc>
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<chapter id="intro">
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<title>Introduction</title>
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<para>
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This framework is designed to provide a standard kernel
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interface to control voltage and current regulators.
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</para>
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<para>
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The intention is to allow systems to dynamically control
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regulator power output in order to save power and prolong
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battery life. This applies to both voltage regulators (where
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voltage output is controllable) and current sinks (where current
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limit is controllable).
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</para>
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<para>
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Note that additional (and currently more complete) documentation
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is available in the Linux kernel source under
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<filename>Documentation/power/regulator</filename>.
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</para>
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<sect1 id="glossary">
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<title>Glossary</title>
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<para>
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The regulator API uses a number of terms which may not be
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familiar:
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</para>
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<glossary>
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<glossentry>
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<glossterm>Regulator</glossterm>
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<glossdef>
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<para>
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Electronic device that supplies power to other devices. Most
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regulators can enable and disable their output and some can also
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control their output voltage or current.
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</para>
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</glossdef>
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</glossentry>
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<glossentry>
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<glossterm>Consumer</glossterm>
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<glossdef>
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<para>
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Electronic device which consumes power provided by a regulator.
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These may either be static, requiring only a fixed supply, or
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dynamic, requiring active management of the regulator at
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runtime.
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</para>
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</glossdef>
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</glossentry>
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<glossentry>
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<glossterm>Power Domain</glossterm>
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<glossdef>
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<para>
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The electronic circuit supplied by a given regulator, including
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the regulator and all consumer devices. The configuration of
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the regulator is shared between all the components in the
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circuit.
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</para>
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</glossdef>
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</glossentry>
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<glossentry>
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<glossterm>Power Management Integrated Circuit</glossterm>
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<acronym>PMIC</acronym>
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<glossdef>
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<para>
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An IC which contains numerous regulators and often also other
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subsystems. In an embedded system the primary PMIC is often
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equivalent to a combination of the PSU and southbridge in a
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desktop system.
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</para>
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</glossdef>
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</glossentry>
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</glossary>
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</sect1>
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</chapter>
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<chapter id="consumer">
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<title>Consumer driver interface</title>
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<para>
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This offers a similar API to the kernel clock framework.
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Consumer drivers use <link
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linkend='API-regulator-get'>get</link> and <link
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linkend='API-regulator-put'>put</link> operations to acquire and
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release regulators. Functions are
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provided to <link linkend='API-regulator-enable'>enable</link>
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and <link linkend='API-regulator-disable'>disable</link> the
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regulator and to get and set the runtime parameters of the
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regulator.
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</para>
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<para>
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When requesting regulators consumers use symbolic names for their
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supplies, such as "Vcc", which are mapped into actual regulator
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devices by the machine interface.
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</para>
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<para>
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A stub version of this API is provided when the regulator
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framework is not in use in order to minimise the need to use
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ifdefs.
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</para>
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<sect1 id="consumer-enable">
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<title>Enabling and disabling</title>
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<para>
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The regulator API provides reference counted enabling and
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disabling of regulators. Consumer devices use the <function><link
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linkend='API-regulator-enable'>regulator_enable</link></function>
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and <function><link
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linkend='API-regulator-disable'>regulator_disable</link>
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</function> functions to enable and disable regulators. Calls
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to the two functions must be balanced.
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</para>
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<para>
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Note that since multiple consumers may be using a regulator and
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machine constraints may not allow the regulator to be disabled
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there is no guarantee that calling
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<function>regulator_disable</function> will actually cause the
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supply provided by the regulator to be disabled. Consumer
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drivers should assume that the regulator may be enabled at all
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times.
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</para>
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</sect1>
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<sect1 id="consumer-config">
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<title>Configuration</title>
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<para>
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Some consumer devices may need to be able to dynamically
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configure their supplies. For example, MMC drivers may need to
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select the correct operating voltage for their cards. This may
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be done while the regulator is enabled or disabled.
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</para>
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<para>
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The <function><link
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linkend='API-regulator-set-voltage'>regulator_set_voltage</link>
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</function> and <function><link
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linkend='API-regulator-set-current-limit'
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>regulator_set_current_limit</link>
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</function> functions provide the primary interface for this.
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Both take ranges of voltages and currents, supporting drivers
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that do not require a specific value (eg, CPU frequency scaling
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normally permits the CPU to use a wider range of supply
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voltages at lower frequencies but does not require that the
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supply voltage be lowered). Where an exact value is required
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both minimum and maximum values should be identical.
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</para>
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</sect1>
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<sect1 id="consumer-callback">
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<title>Callbacks</title>
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<para>
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Callbacks may also be <link
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linkend='API-regulator-register-notifier'>registered</link>
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for events such as regulation failures.
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</para>
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</sect1>
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</chapter>
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<chapter id="driver">
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<title>Regulator driver interface</title>
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<para>
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Drivers for regulator chips <link
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linkend='API-regulator-register'>register</link> the regulators
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with the regulator core, providing operations structures to the
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core. A <link
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linkend='API-regulator-notifier-call-chain'>notifier</link> interface
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allows error conditions to be reported to the core.
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</para>
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<para>
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Registration should be triggered by explicit setup done by the
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platform, supplying a <link
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linkend='API-struct-regulator-init-data'>struct
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regulator_init_data</link> for the regulator containing
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<link linkend='machine-constraint'>constraint</link> and
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<link linkend='machine-supply'>supply</link> information.
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</para>
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</chapter>
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<chapter id="machine">
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<title>Machine interface</title>
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<para>
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This interface provides a way to define how regulators are
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connected to consumers on a given system and what the valid
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operating parameters are for the system.
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</para>
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<sect1 id="machine-supply">
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<title>Supplies</title>
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<para>
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Regulator supplies are specified using <link
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linkend='API-struct-regulator-consumer-supply'>struct
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regulator_consumer_supply</link>. This is done at
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<link linkend='driver'>driver registration
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time</link> as part of the machine constraints.
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</para>
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</sect1>
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<sect1 id="machine-constraint">
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<title>Constraints</title>
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<para>
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As well as defining the connections the machine interface
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also provides constraints defining the operations that
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clients are allowed to perform and the parameters that may be
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set. This is required since generally regulator devices will
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offer more flexibility than it is safe to use on a given
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system, for example supporting higher supply voltages than the
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consumers are rated for.
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</para>
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<para>
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This is done at <link linkend='driver'>driver
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registration time</link> by providing a <link
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linkend='API-struct-regulation-constraints'>struct
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regulation_constraints</link>.
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</para>
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<para>
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The constraints may also specify an initial configuration for the
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regulator in the constraints, which is particularly useful for
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use with static consumers.
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</para>
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</sect1>
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</chapter>
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<chapter id="api">
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<title>API reference</title>
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<para>
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Due to limitations of the kernel documentation framework and the
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existing layout of the source code the entire regulator API is
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documented here.
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</para>
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!Iinclude/linux/regulator/consumer.h
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!Iinclude/linux/regulator/machine.h
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!Iinclude/linux/regulator/driver.h
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!Edrivers/regulator/core.c
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</chapter>
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</book>
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