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review.evervolv.com / android_kernel_htc_msm8960 / 79d30a581fc405fc63322622cb1517d95ed8f5ce / . / Documentation / power / regulator / overview.txt
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Liam Girdwood8e6f0842008-04-30 17:16:51 +0100[diff] [blame]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 <lg@opensource.wolfsonmicro.com>
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 susbsystems.
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 it's supply voltage or
39 current limit. It only needs to enable or disable it's
40 power supply. It's supply voltage is set by the hardware,
41 bootloader, firmware or kernel board initialisation code.
42
43 Dynamic: consumer needs to change it's supply voltage or
44 current limit to meet operation demands.
45
46
47 o Power Domain - Electronic circuit that is supplied it's 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/ouput 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 over current 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/regulator-sysfs.txt