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Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.

1	===============================
2	rfkill - RF kill switch support
3	===============================
6	.. contents::
7	   :depth: 2
9	Introduction
10	============
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.
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.
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:
25	 - hard block
26		read-only radio block that cannot be overridden by software
28	 - soft block
29		writable radio block (need not be readable) that is set by
30	        the system software.
32	The rfkill subsystem has two parameters, rfkill.default_state and
33	rfkill.master_switch_mode, which are documented in
34	admin-guide/kernel-parameters.rst.
37	Implementation details
38	======================
40	The rfkill subsystem is composed of three main components:
42	 * the rfkill core,
43	 * the deprecated rfkill-input module (an input layer handler, being
44	   replaced by userspace policy code) and
45	 * the rfkill drivers.
47	The rfkill core provides API for kernel drivers to register their radio
48	transmitter with the kernel, methods for turning it on and off and, letting
49	the system know about hardware-disabled states that may be implemented on
50	the device.
52	The rfkill core code also notifies userspace of state changes, and provides
53	ways for userspace to query the current states. See the "Userspace support"
54	section below.
56	When the device is hard-blocked (either by a call to rfkill_set_hw_state()
57	or from query_hw_block) set_block() will be invoked for additional software
58	block, but drivers can ignore the method call since they can use the return
59	value of the function rfkill_set_hw_state() to sync the software state
60	instead of keeping track of calls to set_block(). In fact, drivers should
61	use the return value of rfkill_set_hw_state() unless the hardware actually
62	keeps track of soft and hard block separately.
65	Kernel API
66	==========
69	Drivers for radio transmitters normally implement an rfkill driver.
71	Platform drivers might implement input devices if the rfkill button is just
72	that, a button. If that button influences the hardware then you need to
73	implement an rfkill driver instead. This also applies if the platform provides
74	a way to turn on/off the transmitter(s).
76	For some platforms, it is possible that the hardware state changes during
77	suspend/hibernation, in which case it will be necessary to update the rfkill
78	core with the current state is at resume time.
80	To create an rfkill driver, driver's Kconfig needs to have::
82		depends on RFKILL || !RFKILL
84	to ensure the driver cannot be built-in when rfkill is modular. The !RFKILL
85	case allows the driver to be built when rfkill is not configured, which
86	case all rfkill API can still be used but will be provided by static inlines
87	which compile to almost nothing.
89	Calling rfkill_set_hw_state() when a state change happens is required from
90	rfkill drivers that control devices that can be hard-blocked unless they also
91	assign the poll_hw_block() callback (then the rfkill core will poll the
92	device). Don't do this unless you cannot get the event in any other way.
94	RFKill provides per-switch LED triggers, which can be used to drive LEDs
95	according to the switch state (LED_FULL when blocked, LED_OFF otherwise).
98	Userspace support
99	=================
101	The recommended userspace interface to use is /dev/rfkill, which is a misc
102	character device that allows userspace to obtain and set the state of rfkill
103	devices and sets of devices. It also notifies userspace about device addition
104	and removal. The API is a simple read/write API that is defined in
105	linux/rfkill.h, with one ioctl that allows turning off the deprecated input
106	handler in the kernel for the transition period.
108	Except for the one ioctl, communication with the kernel is done via read()
109	and write() of instances of 'struct rfkill_event'. In this structure, the
110	soft and hard block are properly separated (unlike sysfs, see below) and
111	userspace is able to get a consistent snapshot of all rfkill devices in the
112	system. Also, it is possible to switch all rfkill drivers (or all drivers of
113	a specified type) into a state which also updates the default state for
114	hotplugged devices.
116	After an application opens /dev/rfkill, it can read the current state of all
117	devices. Changes can be either obtained by either polling the descriptor for
118	hotplug or state change events or by listening for uevents emitted by the
119	rfkill core framework.
121	Additionally, each rfkill device is registered in sysfs and emits uevents.
123	rfkill devices issue uevents (with an action of "change"), with the following
124	environment variables set::
130	The contents of these variables corresponds to the "name", "state" and
131	"type" sysfs files explained above.
134	For further details consult Documentation/ABI/stable/sysfs-class-rfkill.
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