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Linux kernel mirror (for testing)
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kernel
os
linux
1=============================================
2Linux voltage and current regulator framework
3=============================================
4
5About
6=====
7
8This framework is designed to provide a standard kernel interface to control
9voltage and current regulators.
10
11The intention is to allow systems to dynamically control regulator power output
12in order to save power and prolong battery life. This applies to both voltage
13regulators (where voltage output is controllable) and current sinks (where
14current limit is controllable).
15
16(C) 2008 Wolfson Microelectronics PLC.
17
18Author: Liam Girdwood <lrg@slimlogic.co.uk>
19
20
21Nomenclature
22============
23
24Some terms used in this document:
25
26 - Regulator
27 - Electronic device that supplies power to other devices.
28 Most regulators can enable and disable their output while
29 some can control their output voltage and or current.
30
31 Input Voltage -> Regulator -> Output Voltage
32
33
34 - PMIC
35 - Power Management IC. An IC that contains numerous
36 regulators and often contains other subsystems.
37
38
39 - Consumer
40 - Electronic device that is supplied power by a regulator.
41 Consumers can be classified into two types:-
42
43 Static: consumer does not change its supply voltage or
44 current limit. It only needs to enable or disable its
45 power supply. Its supply voltage is set by the hardware,
46 bootloader, firmware or kernel board initialisation code.
47
48 Dynamic: consumer needs to change its supply voltage or
49 current limit to meet operation demands.
50
51
52 - Power Domain
53 - Electronic circuit that is supplied its input power by the
54 output power of a regulator, switch or by another power
55 domain.
56
57 The supply regulator may be behind a switch(s). i.e.::
58
59 Regulator -+-> Switch-1 -+-> Switch-2 --> [Consumer A]
60 | |
61 | +-> [Consumer B], [Consumer C]
62 |
63 +-> [Consumer D], [Consumer E]
64
65 That is one regulator and three power domains:
66
67 - Domain 1: Switch-1, Consumers D & E.
68 - Domain 2: Switch-2, Consumers B & C.
69 - Domain 3: Consumer A.
70
71 and this represents a "supplies" relationship:
72
73 Domain-1 --> Domain-2 --> Domain-3.
74
75 A power domain may have regulators that are supplied power
76 by other regulators. i.e.::
77
78 Regulator-1 -+-> Regulator-2 -+-> [Consumer A]
79 |
80 +-> [Consumer B]
81
82 This gives us two regulators and two power domains:
83
84 - Domain 1: Regulator-2, Consumer B.
85 - Domain 2: Consumer A.
86
87 and a "supplies" relationship:
88
89 Domain-1 --> Domain-2
90
91
92 - Constraints
93 - Constraints are used to define power levels for performance
94 and hardware protection. Constraints exist at three levels:
95
96 Regulator Level: This is defined by the regulator hardware
97 operating parameters and is specified in the regulator
98 datasheet. i.e.
99
100 - voltage output is in the range 800mV -> 3500mV.
101 - regulator current output limit is 20mA @ 5V but is
102 10mA @ 10V.
103
104 Power Domain Level: This is defined in software by kernel
105 level board initialisation code. It is used to constrain a
106 power domain to a particular power range. i.e.
107
108 - Domain-1 voltage is 3300mV
109 - Domain-2 voltage is 1400mV -> 1600mV
110 - Domain-3 current limit is 0mA -> 20mA.
111
112 Consumer Level: This is defined by consumer drivers
113 dynamically setting voltage or current limit levels.
114
115 e.g. a consumer backlight driver asks for a current increase
116 from 5mA to 10mA to increase LCD illumination. This passes
117 to through the levels as follows :-
118
119 Consumer: need to increase LCD brightness. Lookup and
120 request next current mA value in brightness table (the
121 consumer driver could be used on several different
122 personalities based upon the same reference device).
123
124 Power Domain: is the new current limit within the domain
125 operating limits for this domain and system state (e.g.
126 battery power, USB power)
127
128 Regulator Domains: is the new current limit within the
129 regulator operating parameters for input/output voltage.
130
131 If the regulator request passes all the constraint tests
132 then the new regulator value is applied.
133
134
135Design
136======
137
138The framework is designed and targeted at SoC based devices but may also be
139relevant to non SoC devices and is split into the following four interfaces:-
140
141
142 1. Consumer driver interface.
143
144 This uses a similar API to the kernel clock interface in that consumer
145 drivers can get and put a regulator (like they can with clocks atm) and
146 get/set voltage, current limit, mode, enable and disable. This should
147 allow consumers complete control over their supply voltage and current
148 limit. This also compiles out if not in use so drivers can be reused in
149 systems with no regulator based power control.
150
151 See Documentation/power/regulator/consumer.rst
152
153 2. Regulator driver interface.
154
155 This allows regulator drivers to register their regulators and provide
156 operations to the core. It also has a notifier call chain for propagating
157 regulator events to clients.
158
159 See Documentation/power/regulator/regulator.rst
160
161 3. Machine interface.
162
163 This interface is for machine specific code and allows the creation of
164 voltage/current domains (with constraints) for each regulator. It can
165 provide regulator constraints that will prevent device damage through
166 overvoltage or overcurrent caused by buggy client drivers. It also
167 allows the creation of a regulator tree whereby some regulators are
168 supplied by others (similar to a clock tree).
169
170 See Documentation/power/regulator/machine.rst
171
172 4. Userspace ABI.
173
174 The framework also exports a lot of useful voltage/current/opmode data to
175 userspace via sysfs. This could be used to help monitor device power
176 consumption and status.
177
178 See Documentation/ABI/testing/sysfs-class-regulator