1 rfkill - RF kill switch support
2 ===============================
5 2. Implementation details
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
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
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
29 2. Implementation details
31 The rfkill subsystem is composed of three main components:
33 * the deprecated rfkill-input module (an input layer handler, being
34 replaced by userspace policy code) and
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
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"
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.
58 Drivers for radio transmitters normally implement an rfkill driver.
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).
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.
69 To create an rfkill driver, driver's Kconfig needs to have
71 depends on RFKILL || !RFKILL
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
75 case all rfkill API can still be used but will be provided by static inlines
76 which compile to almost nothing.
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.
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.
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
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.
107 Additionally, each rfkill device is registered in sysfs and emits uevents.
109 rfkill devices issue uevents (with an action of "change"), with the following
110 environment variables set:
116 The contents of these variables corresponds to the "name", "state" and
117 "type" sysfs files explained above.
120 For further details consult Documentation/ABI/stable/sysfs-class-rfkill.