133 lines · plain
1===============================2rfkill - RF kill switch support3===============================4 5 6.. contents::7 :depth: 28 9Introduction10============11 12The rfkill subsystem provides a generic interface for disabling any radio13transmitter in the system. When a transmitter is blocked, it shall not14radiate any power.15 16The subsystem also provides the ability to react on button presses and17disable all transmitters of a certain type (or all). This is intended for18situations where transmitters need to be turned off, for example on19aircraft.20 21The rfkill subsystem has a concept of "hard" and "soft" block, which22differ little in their meaning (block == transmitters off) but rather in23whether they can be changed or not:24 25 - hard block26 read-only radio block that cannot be overridden by software27 28 - soft block29 writable radio block (need not be readable) that is set by30 the system software.31 32The rfkill subsystem has two parameters, rfkill.default_state and33rfkill.master_switch_mode, which are documented in34admin-guide/kernel-parameters.rst.35 36 37Implementation details38======================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, being44 replaced by userspace policy code) and45 * the rfkill drivers.46 47The rfkill core provides API for kernel drivers to register their radio48transmitter with the kernel, methods for turning it on and off, and letting49the system know about hardware-disabled states that may be implemented on50the device.51 52The rfkill core code also notifies userspace of state changes, and provides53ways 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 software58block, but drivers can ignore the method call since they can use the return59value of the function rfkill_set_hw_state() to sync the software state60instead of keeping track of calls to set_block(). In fact, drivers should61use the return value of rfkill_set_hw_state() unless the hardware actually62keeps track of soft and hard block separately.63 64 65Kernel API66==========67 68Drivers for radio transmitters normally implement an rfkill driver.69 70Platform drivers might implement input devices if the rfkill button is just71that, a button. If that button influences the hardware then you need to72implement an rfkill driver instead. This also applies if the platform provides73a way to turn on/off the transmitter(s).74 75For some platforms, it is possible that the hardware state changes during76suspend/hibernation, in which case it will be necessary to update the rfkill77core with the current state at resume time.78 79To create an rfkill driver, driver's Kconfig needs to have::80 81 depends on RFKILL || !RFKILL82 83to ensure the driver cannot be built-in when rfkill is modular. The !RFKILL84case allows the driver to be built when rfkill is not configured, in which85case all rfkill API can still be used but will be provided by static inlines86which compile to almost nothing.87 88Calling rfkill_set_hw_state() when a state change happens is required from89rfkill drivers that control devices that can be hard-blocked unless they also90assign the poll_hw_block() callback (then the rfkill core will poll the91device). 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 LEDs94according to the switch state (LED_FULL when blocked, LED_OFF otherwise).95 96 97Userspace support98=================99 100The recommended userspace interface to use is /dev/rfkill, which is a misc101character device that allows userspace to obtain and set the state of rfkill102devices and sets of devices. It also notifies userspace about device addition103and removal. The API is a simple read/write API that is defined in104linux/rfkill.h, with one ioctl that allows turning off the deprecated input105handler 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, the109soft and hard block are properly separated (unlike sysfs, see below) and110userspace is able to get a consistent snapshot of all rfkill devices in the111system. Also, it is possible to switch all rfkill drivers (or all drivers of112a specified type) into a state which also updates the default state for113hotplugged devices.114 115After an application opens /dev/rfkill, it can read the current state of all116devices. Changes can be obtained by either polling the descriptor for117hotplug or state change events or by listening for uevents emitted by the118rfkill 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 following123environment variables set::124 125 RFKILL_NAME126 RFKILL_STATE127 RFKILL_TYPE128 129The content of these variables corresponds to the "name", "state" and130"type" sysfs files explained above.131 132For further details consult Documentation/ABI/stable/sysfs-class-rfkill.133