Based on kernel version 4.15. Page generated on 2018-01-29 10:00 EST.
1 =============================== 2 rfkill - RF kill switch support 3 =============================== 4 5 6 .. contents:: 7 :depth: 2 8 9 Introduction 10 ============ 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 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 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. 35 36 37 Implementation details 38 ====================== 39 40 The 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 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. 51 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. 55 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. 63 64 65 Kernel API 66 ========== 67 68 69 Drivers for radio transmitters normally implement an rfkill driver. 70 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). 75 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. 79 80 To create an rfkill driver, driver's Kconfig needs to have:: 81 82 depends on RFKILL || !RFKILL 83 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. 88 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. 93 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). 96 97 98 Userspace support 99 ================= 100 101 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. 107 108 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. 115 116 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. 120 121 Additionally, each rfkill device is registered in sysfs and emits uevents. 122 123 rfkill devices issue uevents (with an action of "change"), with the following 124 environment variables set:: 125 126 RFKILL_NAME 127 RFKILL_STATE 128 RFKILL_TYPE 129 130 The contents of these variables corresponds to the "name", "state" and 131 "type" sysfs files explained above. 132 133 134 For further details consult Documentation/ABI/stable/sysfs-class-rfkill.