regulator: Add basic DocBook manual

Add a basic DocBook manual for the regulator API. This is much more
skeletal than the existing text documentation, the main benefit is to
provide a skeleton for automatic generation of a manual based on the
kerneldoc for the API.

Since large portions of the text are lifted from the existing text format
documentation written by Liam Girdwood much of the credit belongs to
him.
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: NLiam Girdwood <lrg@slimlogic.co.uk>

Documentation/DocBook/Makefile

@@ -12,7 +12,7 @@ DOCBOOKS := z8530book.xml mcabook.xml \
 	    kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml \
 	    gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \
 	    genericirq.xml s390-drivers.xml uio-howto.xml scsi.xml \
-	    mac80211.xml debugobjects.xml sh.xml
+	    mac80211.xml debugobjects.xml sh.xml regulator.xml
 
 ###
 # The build process is as follows (targets):

Documentation/DocBook/regulator.tmpl

+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<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
+       reguator 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 definining the connections the machine interface
+	 also provides constraints definining 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>