linux/Documentation/rfkill.txt
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   1rfkill - RF switch subsystem support
   2====================================
   3
   41 Introduction
   52 Implementation details
   63 Kernel driver guidelines
   73.1 wireless device drivers
   83.2 platform/switch drivers
   93.3 input device drivers
  104 Kernel API
  115 Userspace support
  12
  13
  141. Introduction:
  15
  16The rfkill switch subsystem exists to add a generic interface to circuitry that
  17can enable or disable the signal output of a wireless *transmitter* of any
  18type.  By far, the most common use is to disable radio-frequency transmitters.
  19
  20Note that disabling the signal output means that the the transmitter is to be
  21made to not emit any energy when "blocked".  rfkill is not about blocking data
  22transmissions, it is about blocking energy emission.
  23
  24The rfkill subsystem offers support for keys and switches often found on
  25laptops to enable wireless devices like WiFi and Bluetooth, so that these keys
  26and switches actually perform an action in all wireless devices of a given type
  27attached to the system.
  28
  29The buttons to enable and disable the wireless transmitters are important in
  30situations where the user is for example using his laptop on a location where
  31radio-frequency transmitters _must_ be disabled (e.g. airplanes).
  32
  33Because of this requirement, userspace support for the keys should not be made
  34mandatory.  Because userspace might want to perform some additional smarter
  35tasks when the key is pressed, rfkill provides userspace the possibility to
  36take over the task to handle the key events.
  37
  38===============================================================================
  392: Implementation details
  40
  41The rfkill subsystem is composed of various components: the rfkill class, the
  42rfkill-input module (an input layer handler), and some specific input layer
  43events.
  44
  45The rfkill class provides kernel drivers with an interface that allows them to
  46know when they should enable or disable a wireless network device transmitter.
  47This is enabled by the CONFIG_RFKILL Kconfig option.
  48
  49The rfkill class support makes sure userspace will be notified of all state
  50changes on rfkill devices through uevents.  It provides a notification chain
  51for interested parties in the kernel to also get notified of rfkill state
  52changes in other drivers.  It creates several sysfs entries which can be used
  53by userspace.  See section "Userspace support".
  54
  55The rfkill-input module provides the kernel with the ability to implement a
  56basic response when the user presses a key or button (or toggles a switch)
  57related to rfkill functionality.  It is an in-kernel implementation of default
  58policy of reacting to rfkill-related input events and neither mandatory nor
  59required for wireless drivers to operate.  It is enabled by the
  60CONFIG_RFKILL_INPUT Kconfig option.
  61
  62rfkill-input is a rfkill-related events input layer handler.  This handler will
  63listen to all rfkill key events and will change the rfkill state of the
  64wireless devices accordingly.  With this option enabled userspace could either
  65do nothing or simply perform monitoring tasks.
  66
  67The rfkill-input module also provides EPO (emergency power-off) functionality
  68for all wireless transmitters.  This function cannot be overridden, and it is
  69always active.  rfkill EPO is related to *_RFKILL_ALL input layer events.
  70
  71
  72Important terms for the rfkill subsystem:
  73
  74In order to avoid confusion, we avoid the term "switch" in rfkill when it is
  75referring to an electronic control circuit that enables or disables a
  76transmitter.  We reserve it for the physical device a human manipulates
  77(which is an input device, by the way):
  78
  79rfkill switch:
  80
  81        A physical device a human manipulates.  Its state can be perceived by
  82        the kernel either directly (through a GPIO pin, ACPI GPE) or by its
  83        effect on a rfkill line of a wireless device.
  84
  85rfkill controller:
  86
  87        A hardware circuit that controls the state of a rfkill line, which a
  88        kernel driver can interact with *to modify* that state (i.e. it has
  89        either write-only or read/write access).
  90
  91rfkill line:
  92
  93        An input channel (hardware or software) of a wireless device, which
  94        causes a wireless transmitter to stop emitting energy (BLOCK) when it
  95        is active.  Point of view is extremely important here: rfkill lines are
  96        always seen from the PoV of a wireless device (and its driver).
  97
  98soft rfkill line/software rfkill line:
  99
 100        A rfkill line the wireless device driver can directly change the state
 101        of.  Related to rfkill_state RFKILL_STATE_SOFT_BLOCKED.
 102
 103hard rfkill line/hardware rfkill line:
 104
 105        A rfkill line that works fully in hardware or firmware, and that cannot
 106        be overridden by the kernel driver.  The hardware device or the
 107        firmware just exports its status to the driver, but it is read-only.
 108        Related to rfkill_state RFKILL_STATE_HARD_BLOCKED.
 109
 110The enum rfkill_state describes the rfkill state of a transmitter:
 111
 112When a rfkill line or rfkill controller is in the RFKILL_STATE_UNBLOCKED state,
 113the wireless transmitter (radio TX circuit for example) is *enabled*.  When the
 114it is in the RFKILL_STATE_SOFT_BLOCKED or RFKILL_STATE_HARD_BLOCKED, the
 115wireless transmitter is to be *blocked* from operating.
 116
 117RFKILL_STATE_SOFT_BLOCKED indicates that a call to toggle_radio() can change
 118that state.  RFKILL_STATE_HARD_BLOCKED indicates that a call to toggle_radio()
 119will not be able to change the state and will return with a suitable error if
 120attempts are made to set the state to RFKILL_STATE_UNBLOCKED.
 121
 122RFKILL_STATE_HARD_BLOCKED is used by drivers to signal that the device is
 123locked in the BLOCKED state by a hardwire rfkill line (typically an input pin
 124that, when active, forces the transmitter to be disabled) which the driver
 125CANNOT override.
 126
 127Full rfkill functionality requires two different subsystems to cooperate: the
 128input layer and the rfkill class.  The input layer issues *commands* to the
 129entire system requesting that devices registered to the rfkill class change
 130state.  The way this interaction happens is not complex, but it is not obvious
 131either:
 132
 133Kernel Input layer:
 134
 135        * Generates KEY_WWAN, KEY_WLAN, KEY_BLUETOOTH, SW_RFKILL_ALL, and
 136          other such events when the user presses certain keys, buttons, or
 137          toggles certain physical switches.
 138
 139        THE INPUT LAYER IS NEVER USED TO PROPAGATE STATUS, NOTIFICATIONS OR THE
 140        KIND OF STUFF AN ON-SCREEN-DISPLAY APPLICATION WOULD REPORT.  It is
 141        used to issue *commands* for the system to change behaviour, and these
 142        commands may or may not be carried out by some kernel driver or
 143        userspace application.  It follows that doing user feedback based only
 144        on input events is broken, as there is no guarantee that an input event
 145        will be acted upon.
 146
 147        Most wireless communication device drivers implementing rfkill
 148        functionality MUST NOT generate these events, and have no reason to
 149        register themselves with the input layer.  Doing otherwise is a common
 150        misconception.  There is an API to propagate rfkill status change
 151        information, and it is NOT the input layer.
 152
 153rfkill class:
 154
 155        * Calls a hook in a driver to effectively change the wireless
 156          transmitter state;
 157        * Keeps track of the wireless transmitter state (with help from
 158          the driver);
 159        * Generates userspace notifications (uevents) and a call to a
 160          notification chain (kernel) when there is a wireless transmitter
 161          state change;
 162        * Connects a wireless communications driver with the common rfkill
 163          control system, which, for example, allows actions such as
 164          "switch all bluetooth devices offline" to be carried out by
 165          userspace or by rfkill-input.
 166
 167        THE RFKILL CLASS NEVER ISSUES INPUT EVENTS.  THE RFKILL CLASS DOES
 168        NOT LISTEN TO INPUT EVENTS.  NO DRIVER USING THE RFKILL CLASS SHALL
 169        EVER LISTEN TO, OR ACT ON RFKILL INPUT EVENTS.  Doing otherwise is
 170        a layering violation.
 171
 172        Most wireless data communication drivers in the kernel have just to
 173        implement the rfkill class API to work properly.  Interfacing to the
 174        input layer is not often required (and is very often a *bug*) on
 175        wireless drivers.
 176
 177        Platform drivers often have to attach to the input layer to *issue*
 178        (but never to listen to) rfkill events for rfkill switches, and also to
 179        the rfkill class to export a control interface for the platform rfkill
 180        controllers to the rfkill subsystem.  This does NOT mean the rfkill
 181        switch is attached to a rfkill class (doing so is almost always wrong).
 182        It just means the same kernel module is the driver for different
 183        devices (rfkill switches and rfkill controllers).
 184
 185
 186Userspace input handlers (uevents) or kernel input handlers (rfkill-input):
 187
 188        * Implements the policy of what should happen when one of the input
 189          layer events related to rfkill operation is received.
 190        * Uses the sysfs interface (userspace) or private rfkill API calls
 191          to tell the devices registered with the rfkill class to change
 192          their state (i.e. translates the input layer event into real
 193          action).
 194
 195        * rfkill-input implements EPO by handling EV_SW SW_RFKILL_ALL 0
 196          (power off all transmitters) in a special way: it ignores any
 197          overrides and local state cache and forces all transmitters to the
 198          RFKILL_STATE_SOFT_BLOCKED state (including those which are already
 199          supposed to be BLOCKED).
 200        * rfkill EPO will remain active until rfkill-input receives an
 201          EV_SW SW_RFKILL_ALL 1 event.  While the EPO is active, transmitters
 202          are locked in the blocked state (rfkill will refuse to unblock them).
 203        * rfkill-input implements different policies that the user can
 204          select for handling EV_SW SW_RFKILL_ALL 1.  It will unlock rfkill,
 205          and either do nothing (leave transmitters blocked, but now unlocked),
 206          restore the transmitters to their state before the EPO, or unblock
 207          them all.
 208
 209Userspace uevent handler or kernel platform-specific drivers hooked to the
 210rfkill notifier chain:
 211
 212        * Taps into the rfkill notifier chain or to KOBJ_CHANGE uevents,
 213          in order to know when a device that is registered with the rfkill
 214          class changes state;
 215        * Issues feedback notifications to the user;
 216        * In the rare platforms where this is required, synthesizes an input
 217          event to command all *OTHER* rfkill devices to also change their
 218          statues when a specific rfkill device changes state.
 219
 220
 221===============================================================================
 2223: Kernel driver guidelines
 223
 224Remember: point-of-view is everything for a driver that connects to the rfkill
 225subsystem.  All the details below must be measured/perceived from the point of
 226view of the specific driver being modified.
 227
 228The first thing one needs to know is whether his driver should be talking to
 229the rfkill class or to the input layer.  In rare cases (platform drivers), it
 230could happen that you need to do both, as platform drivers often handle a
 231variety of devices in the same driver.
 232
 233Do not mistake input devices for rfkill controllers.  The only type of "rfkill
 234switch" device that is to be registered with the rfkill class are those
 235directly controlling the circuits that cause a wireless transmitter to stop
 236working (or the software equivalent of them), i.e. what we call a rfkill
 237controller.  Every other kind of "rfkill switch" is just an input device and
 238MUST NOT be registered with the rfkill class.
 239
 240A driver should register a device with the rfkill class when ALL of the
 241following conditions are met (they define a rfkill controller):
 242
 2431. The device is/controls a data communications wireless transmitter;
 244
 2452. The kernel can interact with the hardware/firmware to CHANGE the wireless
 246   transmitter state (block/unblock TX operation);
 247
 2483. The transmitter can be made to not emit any energy when "blocked":
 249   rfkill is not about blocking data transmissions, it is about blocking
 250   energy emission;
 251
 252A driver should register a device with the input subsystem to issue
 253rfkill-related events (KEY_WLAN, KEY_BLUETOOTH, KEY_WWAN, KEY_WIMAX,
 254SW_RFKILL_ALL, etc) when ALL of the folowing conditions are met:
 255
 2561. It is directly related to some physical device the user interacts with, to
 257   command the O.S./firmware/hardware to enable/disable a data communications
 258   wireless transmitter.
 259
 260   Examples of the physical device are: buttons, keys and switches the user
 261   will press/touch/slide/switch to enable or disable the wireless
 262   communication device.
 263
 2642. It is NOT slaved to another device, i.e. there is no other device that
 265   issues rfkill-related input events in preference to this one.
 266
 267   Please refer to the corner cases and examples section for more details.
 268
 269When in doubt, do not issue input events.  For drivers that should generate
 270input events in some platforms, but not in others (e.g. b43), the best solution
 271is to NEVER generate input events in the first place.  That work should be
 272deferred to a platform-specific kernel module (which will know when to generate
 273events through the rfkill notifier chain) or to userspace.  This avoids the
 274usual maintenance problems with DMI whitelisting.
 275
 276
 277Corner cases and examples:
 278====================================
 279
 2801. If the device is an input device that, because of hardware or firmware,
 281causes wireless transmitters to be blocked regardless of the kernel's will, it
 282is still just an input device, and NOT to be registered with the rfkill class.
 283
 2842. If the wireless transmitter switch control is read-only, it is an input
 285device and not to be registered with the rfkill class (and maybe not to be made
 286an input layer event source either, see below).
 287
 2883. If there is some other device driver *closer* to the actual hardware the
 289user interacted with (the button/switch/key) to issue an input event, THAT is
 290the device driver that should be issuing input events.
 291
 292E.g:
 293  [RFKILL slider switch] -- [GPIO hardware] -- [WLAN card rf-kill input]
 294                           (platform driver)    (wireless card driver)
 295
 296The user is closer to the RFKILL slide switch plaform driver, so the driver
 297which must issue input events is the platform driver looking at the GPIO
 298hardware, and NEVER the wireless card driver (which is just a slave).  It is
 299very likely that there are other leaves than just the WLAN card rf-kill input
 300(e.g. a bluetooth card, etc)...
 301
 302On the other hand, some embedded devices do this:
 303
 304  [RFKILL slider switch] -- [WLAN card rf-kill input]
 305                             (wireless card driver)
 306
 307In this situation, the wireless card driver *could* register itself as an input
 308device and issue rf-kill related input events... but in order to AVOID the need
 309for DMI whitelisting, the wireless card driver does NOT do it.  Userspace (HAL)
 310or a platform driver (that exists only on these embedded devices) will do the
 311dirty job of issuing the input events.
 312
 313
 314COMMON MISTAKES in kernel drivers, related to rfkill:
 315====================================
 316
 3171. NEVER confuse input device keys and buttons with input device switches.
 318
 319  1a. Switches are always set or reset.  They report the current state
 320      (on position or off position).
 321
 322  1b. Keys and buttons are either in the pressed or not-pressed state, and
 323      that's it.  A "button" that latches down when you press it, and
 324      unlatches when you press it again is in fact a switch as far as input
 325      devices go.
 326
 327Add the SW_* events you need for switches, do NOT try to emulate a button using
 328KEY_* events just because there is no such SW_* event yet.  Do NOT try to use,
 329for example, KEY_BLUETOOTH when you should be using SW_BLUETOOTH instead.
 330
 3312. Input device switches (sources of EV_SW events) DO store their current state
 332(so you *must* initialize it by issuing a gratuitous input layer event on
 333driver start-up and also when resuming from sleep), and that state CAN be
 334queried from userspace through IOCTLs.  There is no sysfs interface for this,
 335but that doesn't mean you should break things trying to hook it to the rfkill
 336class to get a sysfs interface :-)
 337
 3383. Do not issue *_RFKILL_ALL events by default, unless you are sure it is the
 339correct event for your switch/button.  These events are emergency power-off
 340events when they are trying to turn the transmitters off.  An example of an
 341input device which SHOULD generate *_RFKILL_ALL events is the wireless-kill
 342switch in a laptop which is NOT a hotkey, but a real sliding/rocker switch.
 343An example of an input device which SHOULD NOT generate *_RFKILL_ALL events by
 344default, is any sort of hot key that is type-specific (e.g. the one for WLAN).
 345
 346
 3473.1 Guidelines for wireless device drivers
 348------------------------------------------
 349
 350(in this text, rfkill->foo means the foo field of struct rfkill).
 351
 3521. Each independent transmitter in a wireless device (usually there is only one
 353transmitter per device) should have a SINGLE rfkill class attached to it.
 354
 3552. If the device does not have any sort of hardware assistance to allow the
 356driver to rfkill the device, the driver should emulate it by taking all actions
 357required to silence the transmitter.
 358
 3593. If it is impossible to silence the transmitter (i.e. it still emits energy,
 360even if it is just in brief pulses, when there is no data to transmit and there
 361is no hardware support to turn it off) do NOT lie to the users.  Do not attach
 362it to a rfkill class.  The rfkill subsystem does not deal with data
 363transmission, it deals with energy emission.  If the transmitter is emitting
 364energy, it is not blocked in rfkill terms.
 365
 3664. It doesn't matter if the device has multiple rfkill input lines affecting
 367the same transmitter, their combined state is to be exported as a single state
 368per transmitter (see rule 1).
 369
 370This rule exists because users of the rfkill subsystem expect to get (and set,
 371when possible) the overall transmitter rfkill state, not of a particular rfkill
 372line.
 373
 3745. The wireless device driver MUST NOT leave the transmitter enabled during
 375suspend and hibernation unless:
 376
 377        5.1. The transmitter has to be enabled for some sort of functionality
 378        like wake-on-wireless-packet or autonomous packed forwarding in a mesh
 379        network, and that functionality is enabled for this suspend/hibernation
 380        cycle.
 381
 382AND
 383
 384        5.2. The device was not on a user-requested BLOCKED state before
 385        the suspend (i.e. the driver must NOT unblock a device, not even
 386        to support wake-on-wireless-packet or remain in the mesh).
 387
 388In other words, there is absolutely no allowed scenario where a driver can
 389automatically take action to unblock a rfkill controller (obviously, this deals
 390with scenarios where soft-blocking or both soft and hard blocking is happening.
 391Scenarios where hardware rfkill lines are the only ones blocking the
 392transmitter are outside of this rule, since the wireless device driver does not
 393control its input hardware rfkill lines in the first place).
 394
 3956. During resume, rfkill will try to restore its previous state.
 396
 3977. After a rfkill class is suspended, it will *not* call rfkill->toggle_radio
 398until it is resumed.
 399
 400
 401Example of a WLAN wireless driver connected to the rfkill subsystem:
 402--------------------------------------------------------------------
 403
 404A certain WLAN card has one input pin that causes it to block the transmitter
 405and makes the status of that input pin available (only for reading!) to the
 406kernel driver.  This is a hard rfkill input line (it cannot be overridden by
 407the kernel driver).
 408
 409The card also has one PCI register that, if manipulated by the driver, causes
 410it to block the transmitter.  This is a soft rfkill input line.
 411
 412It has also a thermal protection circuitry that shuts down its transmitter if
 413the card overheats, and makes the status of that protection available (only for
 414reading!) to the kernel driver.  This is also a hard rfkill input line.
 415
 416If either one of these rfkill lines are active, the transmitter is blocked by
 417the hardware and forced offline.
 418
 419The driver should allocate and attach to its struct device *ONE* instance of
 420the rfkill class (there is only one transmitter).
 421
 422It can implement the get_state() hook, and return RFKILL_STATE_HARD_BLOCKED if
 423either one of its two hard rfkill input lines are active.  If the two hard
 424rfkill lines are inactive, it must return RFKILL_STATE_SOFT_BLOCKED if its soft
 425rfkill input line is active.  Only if none of the rfkill input lines are
 426active, will it return RFKILL_STATE_UNBLOCKED.
 427
 428Since the device has a hardware rfkill line, it IS subject to state changes
 429external to rfkill.  Therefore, the driver must make sure that it calls
 430rfkill_force_state() to keep the status always up-to-date, and it must do a
 431rfkill_force_state() on resume from sleep.
 432
 433Every time the driver gets a notification from the card that one of its rfkill
 434lines changed state (polling might be needed on badly designed cards that don't
 435generate interrupts for such events), it recomputes the rfkill state as per
 436above, and calls rfkill_force_state() to update it.
 437
 438The driver should implement the toggle_radio() hook, that:
 439
 4401. Returns an error if one of the hardware rfkill lines are active, and the
 441caller asked for RFKILL_STATE_UNBLOCKED.
 442
 4432. Activates the soft rfkill line if the caller asked for state
 444RFKILL_STATE_SOFT_BLOCKED.  It should do this even if one of the hard rfkill
 445lines are active, effectively double-blocking the transmitter.
 446
 4473. Deactivates the soft rfkill line if none of the hardware rfkill lines are
 448active and the caller asked for RFKILL_STATE_UNBLOCKED.
 449
 450===============================================================================
 4514: Kernel API
 452
 453To build a driver with rfkill subsystem support, the driver should depend on
 454(or select) the Kconfig symbol RFKILL; it should _not_ depend on RKFILL_INPUT.
 455
 456The hardware the driver talks to may be write-only (where the current state
 457of the hardware is unknown), or read-write (where the hardware can be queried
 458about its current state).
 459
 460The rfkill class will call the get_state hook of a device every time it needs
 461to know the *real* current state of the hardware.  This can happen often, but
 462it does not do any polling, so it is not enough on hardware that is subject
 463to state changes outside of the rfkill subsystem.
 464
 465Therefore, calling rfkill_force_state() when a state change happens is
 466mandatory when the device has a hardware rfkill line, or when something else
 467like the firmware could cause its state to be changed without going through the
 468rfkill class.
 469
 470Some hardware provides events when its status changes.  In these cases, it is
 471best for the driver to not provide a get_state hook, and instead register the
 472rfkill class *already* with the correct status, and keep it updated using
 473rfkill_force_state() when it gets an event from the hardware.
 474
 475rfkill_force_state() must be used on the device resume handlers to update the
 476rfkill status, should there be any chance of the device status changing during
 477the sleep.
 478
 479There is no provision for a statically-allocated rfkill struct.  You must
 480use rfkill_allocate() to allocate one.
 481
 482You should:
 483        - rfkill_allocate()
 484        - modify rfkill fields (flags, name)
 485        - modify state to the current hardware state (THIS IS THE ONLY TIME
 486          YOU CAN ACCESS state DIRECTLY)
 487        - rfkill_register()
 488
 489The only way to set a device to the RFKILL_STATE_HARD_BLOCKED state is through
 490a suitable return of get_state() or through rfkill_force_state().
 491
 492When a device is in the RFKILL_STATE_HARD_BLOCKED state, the only way to switch
 493it to a different state is through a suitable return of get_state() or through
 494rfkill_force_state().
 495
 496If toggle_radio() is called to set a device to state RFKILL_STATE_SOFT_BLOCKED
 497when that device is already at the RFKILL_STATE_HARD_BLOCKED state, it should
 498not return an error.  Instead, it should try to double-block the transmitter,
 499so that its state will change from RFKILL_STATE_HARD_BLOCKED to
 500RFKILL_STATE_SOFT_BLOCKED should the hardware blocking cease.
 501
 502Please refer to the source for more documentation.
 503
 504===============================================================================
 5055: Userspace support
 506
 507rfkill devices issue uevents (with an action of "change"), with the following
 508environment variables set:
 509
 510RFKILL_NAME
 511RFKILL_STATE
 512RFKILL_TYPE
 513
 514The ABI for these variables is defined by the sysfs attributes.  It is best
 515to take a quick look at the source to make sure of the possible values.
 516
 517It is expected that HAL will trap those, and bridge them to DBUS, etc.  These
 518events CAN and SHOULD be used to give feedback to the user about the rfkill
 519status of the system.
 520
 521Input devices may issue events that are related to rfkill.  These are the
 522various KEY_* events and SW_* events supported by rfkill-input.c.
 523
 524******IMPORTANT******
 525When rfkill-input is ACTIVE, userspace is NOT TO CHANGE THE STATE OF AN RFKILL
 526SWITCH IN RESPONSE TO AN INPUT EVENT also handled by rfkill-input, unless it
 527has set to true the user_claim attribute for that particular switch.  This rule
 528is *absolute*; do NOT violate it.
 529******IMPORTANT******
 530
 531Userspace must not assume it is the only source of control for rfkill switches.
 532Their state CAN and WILL change due to firmware actions, direct user actions,
 533and the rfkill-input EPO override for *_RFKILL_ALL.
 534
 535When rfkill-input is not active, userspace must initiate a rfkill status
 536change by writing to the "state" attribute in order for anything to happen.
 537
 538Take particular care to implement EV_SW SW_RFKILL_ALL properly.  When that
 539switch is set to OFF, *every* rfkill device *MUST* be immediately put into the
 540RFKILL_STATE_SOFT_BLOCKED state, no questions asked.
 541
 542The following sysfs entries will be created:
 543
 544        name: Name assigned by driver to this key (interface or driver name).
 545        type: Name of the key type ("wlan", "bluetooth", etc).
 546        state: Current state of the transmitter
 547                0: RFKILL_STATE_SOFT_BLOCKED
 548                        transmitter is forced off, but one can override it
 549                        by a write to the state attribute;
 550                1: RFKILL_STATE_UNBLOCKED
 551                        transmiter is NOT forced off, and may operate if
 552                        all other conditions for such operation are met
 553                        (such as interface is up and configured, etc);
 554                2: RFKILL_STATE_HARD_BLOCKED
 555                        transmitter is forced off by something outside of
 556                        the driver's control.  One cannot set a device to
 557                        this state through writes to the state attribute;
 558        claim: 1: Userspace handles events, 0: Kernel handles events
 559
 560Both the "state" and "claim" entries are also writable. For the "state" entry
 561this means that when 1 or 0 is written, the device rfkill state (if not yet in
 562the requested state), will be will be toggled accordingly.
 563
 564For the "claim" entry writing 1 to it means that the kernel no longer handles
 565key events even though RFKILL_INPUT input was enabled. When "claim" has been
 566set to 0, userspace should make sure that it listens for the input events or
 567check the sysfs "state" entry regularly to correctly perform the required tasks
 568when the rkfill key is pressed.
 569
 570A note about input devices and EV_SW events:
 571
 572In order to know the current state of an input device switch (like
 573SW_RFKILL_ALL), you will need to use an IOCTL.  That information is not
 574available through sysfs in a generic way at this time, and it is not available
 575through the rfkill class AT ALL.
 576
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