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1===============================
2rfkill - RF kill switch support
3===============================
4
5
6.. contents::
7 :depth: 2
8
9Introduction
10============
11
12The rfkill subsystem provides a generic interface for disabling any radio
13transmitter in the system. When a transmitter is blocked, it shall not
14radiate any power.
15
16The subsystem also provides the ability to react on button presses and
17disable all transmitters of a certain type (or all). This is intended for
18situations where transmitters need to be turned off, for example on
19aircraft.
20
21The rfkill subsystem has a concept of "hard" and "soft" block, which
22differ little in their meaning (block == transmitters off) but rather in
23whether they can be changed or not:
24
25 - hard block
26 read-only radio block that cannot be overridden by software
27
28 - soft block
29 writable radio block (need not be readable) that is set by
30 the system software.
31
32The rfkill subsystem has two parameters, rfkill.default_state and
33rfkill.master_switch_mode, which are documented in
34admin-guide/kernel-parameters.rst.
35
36
37Implementation details
38======================
39
40The rfkill subsystem is composed of three main components:
41
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.
46
47The rfkill core provides API for kernel drivers to register their radio
48transmitter with the kernel, methods for turning it on and off, and letting
49the system know about hardware-disabled states that may be implemented on
50the device.
51
52The rfkill core code also notifies userspace of state changes, and provides
53ways for userspace to query the current states. See the "Userspace support"
54section below.
55
56When the device is hard-blocked (either by a call to rfkill_set_hw_state()
57or from query_hw_block), set_block() will be invoked for additional software
58block, but drivers can ignore the method call since they can use the return
59value of the function rfkill_set_hw_state() to sync the software state
60instead of keeping track of calls to set_block(). In fact, drivers should
61use the return value of rfkill_set_hw_state() unless the hardware actually
62keeps track of soft and hard block separately.
63
64
65Kernel API
66==========
67
68Drivers for radio transmitters normally implement an rfkill driver.
69
70Platform drivers might implement input devices if the rfkill button is just
71that, a button. If that button influences the hardware then you need to
72implement an rfkill driver instead. This also applies if the platform provides
73a way to turn on/off the transmitter(s).
74
75For some platforms, it is possible that the hardware state changes during
76suspend/hibernation, in which case it will be necessary to update the rfkill
77core with the current state at resume time.
78
79To create an rfkill driver, driver's Kconfig needs to have::
80
81 depends on RFKILL || !RFKILL
82
83to ensure the driver cannot be built-in when rfkill is modular. The !RFKILL
84case allows the driver to be built when rfkill is not configured, in which
85case all rfkill API can still be used but will be provided by static inlines
86which compile to almost nothing.
87
88Calling rfkill_set_hw_state() when a state change happens is required from
89rfkill drivers that control devices that can be hard-blocked unless they also
90assign the poll_hw_block() callback (then the rfkill core will poll the
91device). Don't do this unless you cannot get the event in any other way.
92
93rfkill provides per-switch LED triggers, which can be used to drive LEDs
94according to the switch state (LED_FULL when blocked, LED_OFF otherwise).
95
96
97Userspace support
98=================
99
100The recommended userspace interface to use is /dev/rfkill, which is a misc
101character device that allows userspace to obtain and set the state of rfkill
102devices and sets of devices. It also notifies userspace about device addition
103and removal. The API is a simple read/write API that is defined in
104linux/rfkill.h, with one ioctl that allows turning off the deprecated input
105handler in the kernel for the transition period.
106
107Except for the one ioctl, communication with the kernel is done via read()
108and write() of instances of 'struct rfkill_event'. In this structure, the
109soft and hard block are properly separated (unlike sysfs, see below) and
110userspace is able to get a consistent snapshot of all rfkill devices in the
111system. Also, it is possible to switch all rfkill drivers (or all drivers of
112a specified type) into a state which also updates the default state for
113hotplugged devices.
114
115After an application opens /dev/rfkill, it can read the current state of all
116devices. Changes can be obtained by either polling the descriptor for
117hotplug or state change events or by listening for uevents emitted by the
118rfkill core framework.
119
120Additionally, each rfkill device is registered in sysfs and emits uevents.
121
122rfkill devices issue uevents (with an action of "change"), with the following
123environment variables set::
124
125 RFKILL_NAME
126 RFKILL_STATE
127 RFKILL_TYPE
128
129The content of these variables corresponds to the "name", "state" and
130"type" sysfs files explained above.
131
132For further details consult Documentation/ABI/stable/sysfs-class-rfkill.
1===============================
2rfkill - RF kill switch support
3===============================
4
5
6.. contents::
7 :depth: 2
8
9Introduction
10============
11
12The rfkill subsystem provides a generic interface for disabling any radio
13transmitter in the system. When a transmitter is blocked, it shall not
14radiate any power.
15
16The subsystem also provides the ability to react on button presses and
17disable all transmitters of a certain type (or all). This is intended for
18situations where transmitters need to be turned off, for example on
19aircraft.
20
21The rfkill subsystem has a concept of "hard" and "soft" block, which
22differ little in their meaning (block == transmitters off) but rather in
23whether they can be changed or not:
24
25 - hard block
26 read-only radio block that cannot be overridden by software
27
28 - soft block
29 writable radio block (need not be readable) that is set by
30 the system software.
31
32The rfkill subsystem has two parameters, rfkill.default_state and
33rfkill.master_switch_mode, which are documented in
34admin-guide/kernel-parameters.rst.
35
36
37Implementation details
38======================
39
40The rfkill subsystem is composed of three main components:
41
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.
46
47The rfkill core provides API for kernel drivers to register their radio
48transmitter with the kernel, methods for turning it on and off, and letting
49the system know about hardware-disabled states that may be implemented on
50the device.
51
52The rfkill core code also notifies userspace of state changes, and provides
53ways for userspace to query the current states. See the "Userspace support"
54section below.
55
56When the device is hard-blocked (either by a call to rfkill_set_hw_state()
57or from query_hw_block), set_block() will be invoked for additional software
58block, but drivers can ignore the method call since they can use the return
59value of the function rfkill_set_hw_state() to sync the software state
60instead of keeping track of calls to set_block(). In fact, drivers should
61use the return value of rfkill_set_hw_state() unless the hardware actually
62keeps track of soft and hard block separately.
63
64
65Kernel API
66==========
67
68Drivers for radio transmitters normally implement an rfkill driver.
69
70Platform drivers might implement input devices if the rfkill button is just
71that, a button. If that button influences the hardware then you need to
72implement an rfkill driver instead. This also applies if the platform provides
73a way to turn on/off the transmitter(s).
74
75For some platforms, it is possible that the hardware state changes during
76suspend/hibernation, in which case it will be necessary to update the rfkill
77core with the current state at resume time.
78
79To create an rfkill driver, driver's Kconfig needs to have::
80
81 depends on RFKILL || !RFKILL
82
83to ensure the driver cannot be built-in when rfkill is modular. The !RFKILL
84case allows the driver to be built when rfkill is not configured, in which
85case all rfkill API can still be used but will be provided by static inlines
86which compile to almost nothing.
87
88Calling rfkill_set_hw_state() when a state change happens is required from
89rfkill drivers that control devices that can be hard-blocked unless they also
90assign the poll_hw_block() callback (then the rfkill core will poll the
91device). Don't do this unless you cannot get the event in any other way.
92
93rfkill provides per-switch LED triggers, which can be used to drive LEDs
94according to the switch state (LED_FULL when blocked, LED_OFF otherwise).
95
96
97Userspace support
98=================
99
100The recommended userspace interface to use is /dev/rfkill, which is a misc
101character device that allows userspace to obtain and set the state of rfkill
102devices and sets of devices. It also notifies userspace about device addition
103and removal. The API is a simple read/write API that is defined in
104linux/rfkill.h, with one ioctl that allows turning off the deprecated input
105handler in the kernel for the transition period.
106
107Except for the one ioctl, communication with the kernel is done via read()
108and write() of instances of 'struct rfkill_event'. In this structure, the
109soft and hard block are properly separated (unlike sysfs, see below) and
110userspace is able to get a consistent snapshot of all rfkill devices in the
111system. Also, it is possible to switch all rfkill drivers (or all drivers of
112a specified type) into a state which also updates the default state for
113hotplugged devices.
114
115After an application opens /dev/rfkill, it can read the current state of all
116devices. Changes can be obtained by either polling the descriptor for
117hotplug or state change events or by listening for uevents emitted by the
118rfkill core framework.
119
120Additionally, each rfkill device is registered in sysfs and emits uevents.
121
122rfkill devices issue uevents (with an action of "change"), with the following
123environment variables set::
124
125 RFKILL_NAME
126 RFKILL_STATE
127 RFKILL_TYPE
128
129The content of these variables corresponds to the "name", "state" and
130"type" sysfs files explained above.
131
132For further details consult Documentation/ABI/stable/sysfs-class-rfkill.