linux-imx

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rfkill - RF kill switch support

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Introduction

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The rfkill subsystem provides a generic interface for disabling any radio

transmitter in the system. When a transmitter is blocked, it shall not

radiate any power.

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The subsystem also provides the ability to react on button presses and

disable all transmitters of a certain type (or all). This is intended for

situations where transmitters need to be turned off, for example on

aircraft.

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The rfkill subsystem has a concept of "hard" and "soft" block, which

differ little in their meaning (block == transmitters off) but rather in

whether they can be changed or not:

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 - hard block

    read-only radio block that cannot be overridden by software

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 - soft block

    writable radio block (need not be readable) that is set by

        the system software.

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The rfkill subsystem has two parameters, rfkill.default_state and

rfkill.master_switch_mode, which are documented in

admin-guide/kernel-parameters.rst.

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Implementation details

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The rfkill subsystem is composed of three main components:

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 * the rfkill core,

 * the deprecated rfkill-input module (an input layer handler, being

   replaced by userspace policy code) and

 * the rfkill drivers.

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The rfkill core provides API for kernel drivers to register their radio

transmitter with the kernel, methods for turning it on and off, and letting

the system know about hardware-disabled states that may be implemented on

the device.

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The rfkill core code also notifies userspace of state changes, and provides

ways for userspace to query the current states. See the "Userspace support"

section below.

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When the device is hard-blocked (either by a call to rfkill_set_hw_state()

or from query_hw_block), set_block() will be invoked for additional software

block, but drivers can ignore the method call since they can use the return

value of the function rfkill_set_hw_state() to sync the software state

instead of keeping track of calls to set_block(). In fact, drivers should

use the return value of rfkill_set_hw_state() unless the hardware actually

keeps track of soft and hard block separately.

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