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Source at commit b386be689295730688885552666ea40b2e639b14 created 11 years 11 months ago. By Maarten ter Huurne, Revert "MIPS: JZ4740: reset: Initialize hibernate wakeup counters." | |
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1 | rfkill - RF kill switch support |
2 | =============================== |
3 | |
4 | 1. Introduction |
5 | 2. Implementation details |
6 | 3. Kernel API |
7 | 4. Userspace support |
8 | |
9 | |
10 | 1. Introduction |
11 | |
12 | The rfkill subsystem provides a generic interface to disabling any radio |
13 | transmitter in the system. When a transmitter is blocked, it shall not |
14 | radiate any power. |
15 | |
16 | The subsystem also provides the ability to react on button presses and |
17 | disable all transmitters of a certain type (or all). This is intended for |
18 | situations where transmitters need to be turned off, for example on |
19 | aircraft. |
20 | |
21 | The rfkill subsystem has a concept of "hard" and "soft" block, which |
22 | differ little in their meaning (block == transmitters off) but rather in |
23 | whether they can be changed or not: |
24 | - hard block: read-only radio block that cannot be overriden by software |
25 | - soft block: writable radio block (need not be readable) that is set by |
26 | the system software. |
27 | |
28 | |
29 | 2. Implementation details |
30 | |
31 | The rfkill subsystem is composed of three main components: |
32 | * the rfkill core, |
33 | * the deprecated rfkill-input module (an input layer handler, being |
34 | replaced by userspace policy code) and |
35 | * the rfkill drivers. |
36 | |
37 | The rfkill core provides API for kernel drivers to register their radio |
38 | transmitter with the kernel, methods for turning it on and off and, letting |
39 | the system know about hardware-disabled states that may be implemented on |
40 | the device. |
41 | |
42 | The rfkill core code also notifies userspace of state changes, and provides |
43 | ways for userspace to query the current states. See the "Userspace support" |
44 | section below. |
45 | |
46 | When the device is hard-blocked (either by a call to rfkill_set_hw_state() |
47 | or from query_hw_block) set_block() will be invoked for additional software |
48 | block, but drivers can ignore the method call since they can use the return |
49 | value of the function rfkill_set_hw_state() to sync the software state |
50 | instead of keeping track of calls to set_block(). In fact, drivers should |
51 | use the return value of rfkill_set_hw_state() unless the hardware actually |
52 | keeps track of soft and hard block separately. |
53 | |
54 | |
55 | 3. Kernel API |
56 | |
57 | |
58 | Drivers for radio transmitters normally implement an rfkill driver. |
59 | |
60 | Platform drivers might implement input devices if the rfkill button is just |
61 | that, a button. If that button influences the hardware then you need to |
62 | implement an rfkill driver instead. This also applies if the platform provides |
63 | a way to turn on/off the transmitter(s). |
64 | |
65 | For some platforms, it is possible that the hardware state changes during |
66 | suspend/hibernation, in which case it will be necessary to update the rfkill |
67 | core with the current state is at resume time. |
68 | |
69 | To create an rfkill driver, driver's Kconfig needs to have |
70 | |
71 | depends on RFKILL || !RFKILL |
72 | |
73 | to ensure the driver cannot be built-in when rfkill is modular. The !RFKILL |
74 | case allows the driver to be built when rfkill is not configured, which which |
75 | case all rfkill API can still be used but will be provided by static inlines |
76 | which compile to almost nothing. |
77 | |
78 | Calling rfkill_set_hw_state() when a state change happens is required from |
79 | rfkill drivers that control devices that can be hard-blocked unless they also |
80 | assign the poll_hw_block() callback (then the rfkill core will poll the |
81 | device). Don't do this unless you cannot get the event in any other way. |
82 | |
83 | |
84 | |
85 | 5. Userspace support |
86 | |
87 | The recommended userspace interface to use is /dev/rfkill, which is a misc |
88 | character device that allows userspace to obtain and set the state of rfkill |
89 | devices and sets of devices. It also notifies userspace about device addition |
90 | and removal. The API is a simple read/write API that is defined in |
91 | linux/rfkill.h, with one ioctl that allows turning off the deprecated input |
92 | handler in the kernel for the transition period. |
93 | |
94 | Except for the one ioctl, communication with the kernel is done via read() |
95 | and write() of instances of 'struct rfkill_event'. In this structure, the |
96 | soft and hard block are properly separated (unlike sysfs, see below) and |
97 | userspace is able to get a consistent snapshot of all rfkill devices in the |
98 | system. Also, it is possible to switch all rfkill drivers (or all drivers of |
99 | a specified type) into a state which also updates the default state for |
100 | hotplugged devices. |
101 | |
102 | After an application opens /dev/rfkill, it can read the current state of all |
103 | devices. Changes can be either obtained by either polling the descriptor for |
104 | hotplug or state change events or by listening for uevents emitted by the |
105 | rfkill core framework. |
106 | |
107 | Additionally, each rfkill device is registered in sysfs and emits uevents. |
108 | |
109 | rfkill devices issue uevents (with an action of "change"), with the following |
110 | environment variables set: |
111 | |
112 | RFKILL_NAME |
113 | RFKILL_STATE |
114 | RFKILL_TYPE |
115 | |
116 | The contents of these variables corresponds to the "name", "state" and |
117 | "type" sysfs files explained above. |
118 | |
119 | |
120 | For further details consult Documentation/ABI/stable/sysfs-class-rfkill. |
121 |
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