regulator.rst (6007B)
1.. Copyright 2007-2008 Wolfson Microelectronics 2 3.. This documentation is free software; you can redistribute 4.. it and/or modify it under the terms of the GNU General Public 5.. License version 2 as published by the Free Software Foundation. 6 7================================= 8Voltage and current regulator API 9================================= 10 11:Author: Liam Girdwood 12:Author: Mark Brown 13 14Introduction 15============ 16 17This framework is designed to provide a standard kernel interface to 18control voltage and current regulators. 19 20The intention is to allow systems to dynamically control regulator power 21output in order to save power and prolong battery life. This applies to 22both voltage regulators (where voltage output is controllable) and 23current sinks (where current limit is controllable). 24 25Note that additional (and currently more complete) documentation is 26available in the Linux kernel source under 27``Documentation/power/regulator``. 28 29Glossary 30-------- 31 32The regulator API uses a number of terms which may not be familiar: 33 34Regulator 35 36 Electronic device that supplies power to other devices. Most regulators 37 can enable and disable their output and some can also control their 38 output voltage or current. 39 40Consumer 41 42 Electronic device which consumes power provided by a regulator. These 43 may either be static, requiring only a fixed supply, or dynamic, 44 requiring active management of the regulator at runtime. 45 46Power Domain 47 48 The electronic circuit supplied by a given regulator, including the 49 regulator and all consumer devices. The configuration of the regulator 50 is shared between all the components in the circuit. 51 52Power Management Integrated Circuit (PMIC) 53 54 An IC which contains numerous regulators and often also other 55 subsystems. In an embedded system the primary PMIC is often equivalent 56 to a combination of the PSU and southbridge in a desktop system. 57 58Consumer driver interface 59========================= 60 61This offers a similar API to the kernel clock framework. Consumer 62drivers use `get <#API-regulator-get>`__ and 63`put <#API-regulator-put>`__ operations to acquire and release 64regulators. Functions are provided to `enable <#API-regulator-enable>`__ 65and `disable <#API-regulator-disable>`__ the regulator and to get and 66set the runtime parameters of the regulator. 67 68When requesting regulators consumers use symbolic names for their 69supplies, such as "Vcc", which are mapped into actual regulator devices 70by the machine interface. 71 72A stub version of this API is provided when the regulator framework is 73not in use in order to minimise the need to use ifdefs. 74 75Enabling and disabling 76---------------------- 77 78The regulator API provides reference counted enabling and disabling of 79regulators. Consumer devices use the :c:func:`regulator_enable()` and 80:c:func:`regulator_disable()` functions to enable and disable 81regulators. Calls to the two functions must be balanced. 82 83Note that since multiple consumers may be using a regulator and machine 84constraints may not allow the regulator to be disabled there is no 85guarantee that calling :c:func:`regulator_disable()` will actually 86cause the supply provided by the regulator to be disabled. Consumer 87drivers should assume that the regulator may be enabled at all times. 88 89Configuration 90------------- 91 92Some consumer devices may need to be able to dynamically configure their 93supplies. For example, MMC drivers may need to select the correct 94operating voltage for their cards. This may be done while the regulator 95is enabled or disabled. 96 97The :c:func:`regulator_set_voltage()` and 98:c:func:`regulator_set_current_limit()` functions provide the primary 99interface for this. Both take ranges of voltages and currents, supporting 100drivers that do not require a specific value (eg, CPU frequency scaling 101normally permits the CPU to use a wider range of supply voltages at lower 102frequencies but does not require that the supply voltage be lowered). Where 103an exact value is required both minimum and maximum values should be 104identical. 105 106Callbacks 107--------- 108 109Callbacks may also be registered for events such as regulation failures. 110 111Regulator driver interface 112========================== 113 114Drivers for regulator chips register the regulators with the regulator 115core, providing operations structures to the core. A notifier interface 116allows error conditions to be reported to the core. 117 118Registration should be triggered by explicit setup done by the platform, 119supplying a struct regulator_init_data for the regulator 120containing constraint and supply information. 121 122Machine interface 123================= 124 125This interface provides a way to define how regulators are connected to 126consumers on a given system and what the valid operating parameters are 127for the system. 128 129Supplies 130-------- 131 132Regulator supplies are specified using struct 133:c:type:`regulator_consumer_supply`. This is done at driver registration 134time as part of the machine constraints. 135 136Constraints 137----------- 138 139As well as defining the connections the machine interface also provides 140constraints defining the operations that clients are allowed to perform 141and the parameters that may be set. This is required since generally 142regulator devices will offer more flexibility than it is safe to use on 143a given system, for example supporting higher supply voltages than the 144consumers are rated for. 145 146This is done at driver registration time` by providing a 147struct regulation_constraints. 148 149The constraints may also specify an initial configuration for the 150regulator in the constraints, which is particularly useful for use with 151static consumers. 152 153API reference 154============= 155 156Due to limitations of the kernel documentation framework and the 157existing layout of the source code the entire regulator API is 158documented here. 159 160.. kernel-doc:: include/linux/regulator/consumer.h 161 :internal: 162 163.. kernel-doc:: include/linux/regulator/machine.h 164 :internal: 165 166.. kernel-doc:: include/linux/regulator/driver.h 167 :internal: 168 169.. kernel-doc:: drivers/regulator/core.c 170 :export: