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Based on kernel version 3.13. Page generated on 2014-01-20 22:04 EST.

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.
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