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rfkill - RF kill switch support3
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:depth: 28
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Introduction10
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The rfkill subsystem provides a generic interface to disabling any radio12
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The rfkill subsystem provides a generic interface for disabling any radio13
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transmitter in the system. When a transmitter is blocked, it shall not14
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radiate any power.15
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The subsystem also provides the ability to react on button presses and17
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disable all transmitters of a certain type (or all). This is intended for18
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situations where transmitters need to be turned off, for example on19
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aircraft.20
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The rfkill subsystem has a concept of "hard" and "soft" block, which22
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differ little in their meaning (block == transmitters off) but rather in38
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The rfkill subsystem is composed of three main components:41
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* the rfkill core,43
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* the deprecated rfkill-input module (an input layer handler, being44
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replaced by userspace policy code) and45
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* the rfkill drivers.46
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The rfkill core provides API for kernel drivers to register their radio48
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transmitter with the kernel, methods for turning it on and off and, letting48
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transmitter with the kernel, methods for turning it on and off, and letting49
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the system know about hardware-disabled states that may be implemented on50
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the device.51
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The rfkill core code also notifies userspace of state changes, and provides53
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ways for userspace to query the current states. See the "Userspace support"54
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section below.55
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When the device is hard-blocked (either by a call to rfkill_set_hw_state()57
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or from query_hw_block) set_block() will be invoked for additional software57
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or from query_hw_block), set_block() will be invoked for additional software58
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block, but drivers can ignore the method call since they can use the return59
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value of the function rfkill_set_hw_state() to sync the software state60
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instead of keeping track of calls to set_block(). In fact, drivers should61
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use the return value of rfkill_set_hw_state() unless the hardware actually62
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keeps track of soft and hard block separately.63
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Kernel API66
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Drivers for radio transmitters normally implement an rfkill driver.70
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Platform drivers might implement input devices if the rfkill button is just72
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that, a button. If that button influences the hardware then you need to73
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implement an rfkill driver instead. This also applies if the platform provides74
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a way to turn on/off the transmitter(s).75
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For some platforms, it is possible that the hardware state changes during77
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suspend/hibernation, in which case it will be necessary to update the rfkill78
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core with the current state is at resume time.77
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core with the current state at resume time.79
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To create an rfkill driver, driver's Kconfig needs to have::81
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depends on RFKILL || !RFKILL83
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to ensure the driver cannot be built-in when rfkill is modular. The !RFKILL85
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case allows the driver to be built when rfkill is not configured, which84
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case allows the driver to be built when rfkill is not configured, in which86
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case all rfkill API can still be used but will be provided by static inlines87
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which compile to almost nothing.88
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Calling rfkill_set_hw_state() when a state change happens is required from90
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rfkill drivers that control devices that can be hard-blocked unless they also91
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assign the poll_hw_block() callback (then the rfkill core will poll the92
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device). Don't do this unless you cannot get the event in any other way.93
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RFKill provides per-switch LED triggers, which can be used to drive LEDs93
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rfkill provides per-switch LED triggers, which can be used to drive LEDs95
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according to the switch state (LED_FULL when blocked, LED_OFF otherwise).96
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Userspace support99
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=================100
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The recommended userspace interface to use is /dev/rfkill, which is a misc102
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character device that allows userspace to obtain and set the state of rfkill103
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devices and sets of devices. It also notifies userspace about device addition104
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and removal. The API is a simple read/write API that is defined in107
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Except for the one ioctl, communication with the kernel is done via read()109
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and write() of instances of 'struct rfkill_event'. In this structure, the110
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soft and hard block are properly separated (unlike sysfs, see below) and111
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userspace is able to get a consistent snapshot of all rfkill devices in the112
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system. Also, it is possible to switch all rfkill drivers (or all drivers of113
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a specified type) into a state which also updates the default state for114
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hotplugged devices.115
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After an application opens /dev/rfkill, it can read the current state of all117
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devices. Changes can be either obtained by either polling the descriptor for116
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devices. Changes can be obtained by either polling the descriptor for118
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hotplug or state change events or by listening for uevents emitted by the119
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rfkill core framework.120
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Additionally, each rfkill device is registered in sysfs and emits uevents.122
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rfkill devices issue uevents (with an action of "change"), with the following124
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environment variables set::125
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RFKILL_NAME127
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RFKILL_STATE128
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RFKILL_TYPE129
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The contents of these variables corresponds to the "name", "state" and129
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The content of these variables corresponds to the "name", "state" and131
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"type" sysfs files explained above.132
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For further details consult Documentation/ABI/stable/sysfs-class-rfkill.