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