rfkill: rewrite

This patch completely rewrites the rfkill core to address
the following deficiencies:

 * all rfkill drivers need to implement polling where necessary
   rather than having one central implementation

 * updating the rfkill state cannot be done from arbitrary
   contexts, forcing drivers to use schedule_work and requiring
   lots of code

 * rfkill drivers need to keep track of soft/hard blocked
   internally -- the core should do this

 * the rfkill API has many unexpected quirks, for example being
   asymmetric wrt. alloc/free and register/unregister

 * rfkill can call back into a driver from within a function the
   driver called -- this is prone to deadlocks and generally
   should be avoided

 * rfkill-input pointlessly is a separate module

 * drivers need to #ifdef rfkill functions (unless they want to
   depend on or select RFKILL) -- rfkill should provide inlines
   that do nothing if it isn't compiled in

 * the rfkill structure is not opaque -- drivers need to initialise
   it correctly (lots of sanity checking code required) -- instead
   force drivers to pass the right variables to rfkill_alloc()

 * the documentation is hard to read because it always assumes the
   reader is completely clueless and contains way TOO MANY CAPS

 * the rfkill code needlessly uses a lot of locks and atomic
   operations in locked sections

 * fix LED trigger to actually change the LED when the radio state
   changes -- this wasn't done before

Tested-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br> [thinkpad]
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 78 insertions, 519 deletions

diff --git a/Documentation/rfkill.txt b/Documentation/rfkill.txt
index 40c3a3f10816..de941e309d47 100644
--- a/Documentation/rfkill.txt
+++ b/Documentation/rfkill.txt
@@ -1,571 +1,130 @@
-rfkill - RF switch subsystem support
-====================================
+rfkill - RF kill switch support
+===============================
 
-1 Introduction
-2 Implementation details
-3 Kernel driver guidelines
-3.1 wireless device drivers
-3.2 platform/switch drivers
-3.3 input device drivers
-4 Kernel API
-5 Userspace support
+1. Introduction
+2. Implementation details
+3. Kernel driver guidelines
+4. Kernel API
+5. Userspace support
 
 
-1. Introduction:
+1. Introduction
 
-The rfkill switch subsystem exists to add a generic interface to circuitry that
-can enable or disable the signal output of a wireless *transmitter* of any
-type.  By far, the most common use is to disable radio-frequency transmitters.
+The rfkill subsystem provides a generic interface to disabling any radio
+transmitter in the system. When a transmitter is blocked, it shall not
+radiate any power.
 
-Note that disabling the signal output means that the the transmitter is to be
-made to not emit any energy when "blocked".  rfkill is not about blocking data
-transmissions, it is about blocking energy emission.
+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.
 
-The rfkill subsystem offers support for keys and switches often found on
-laptops to enable wireless devices like WiFi and Bluetooth, so that these keys
-and switches actually perform an action in all wireless devices of a given type
-attached to the system.
 
-The buttons to enable and disable the wireless transmitters are important in
-situations where the user is for example using his laptop on a location where
-radio-frequency transmitters _must_ be disabled (e.g. airplanes).
 
-Because of this requirement, userspace support for the keys should not be made
-mandatory.  Because userspace might want to perform some additional smarter
-tasks when the key is pressed, rfkill provides userspace the possibility to
-take over the task to handle the key events.
-
-===============================================================================
-2: Implementation details
+2. Implementation details
 
 The rfkill subsystem is composed of various components: the rfkill class, the
 rfkill-input module (an input layer handler), and some specific input layer
 events.
 
-The rfkill class provides kernel drivers with an interface that allows them to
-know when they should enable or disable a wireless network device transmitter.
-This is enabled by the CONFIG_RFKILL Kconfig option.
-
-The rfkill class support makes sure userspace will be notified of all state
-changes on rfkill devices through uevents.  It provides a notification chain
-for interested parties in the kernel to also get notified of rfkill state
-changes in other drivers.  It creates several sysfs entries which can be used
-by userspace.  See section "Userspace support".
-
-The rfkill-input module provides the kernel with the ability to implement a
-basic response when the user presses a key or button (or toggles a switch)
-related to rfkill functionality.  It is an in-kernel implementation of default
-policy of reacting to rfkill-related input events and neither mandatory nor
-required for wireless drivers to operate.  It is enabled by the
-CONFIG_RFKILL_INPUT Kconfig option.
-
-rfkill-input is a rfkill-related events input layer handler.  This handler will
-listen to all rfkill key events and will change the rfkill state of the
-wireless devices accordingly.  With this option enabled userspace could either
-do nothing or simply perform monitoring tasks.
-
-The rfkill-input module also provides EPO (emergency power-off) functionality
-for all wireless transmitters.  This function cannot be overridden, and it is
-always active.  rfkill EPO is related to *_RFKILL_ALL input layer events.
-
-
-Important terms for the rfkill subsystem:
-
-In order to avoid confusion, we avoid the term "switch" in rfkill when it is
-referring to an electronic control circuit that enables or disables a
-transmitter.  We reserve it for the physical device a human manipulates
-(which is an input device, by the way):
-
-rfkill switch:
-
-        A physical device a human manipulates.  Its state can be perceived by
-        the kernel either directly (through a GPIO pin, ACPI GPE) or by its
-        effect on a rfkill line of a wireless device.
-
-rfkill controller:
-
-        A hardware circuit that controls the state of a rfkill line, which a
-        kernel driver can interact with *to modify* that state (i.e. it has
-        either write-only or read/write access).
-
-rfkill line:
-
-        An input channel (hardware or software) of a wireless device, which
-        causes a wireless transmitter to stop emitting energy (BLOCK) when it
-        is active.  Point of view is extremely important here: rfkill lines are
-        always seen from the PoV of a wireless device (and its driver).
-
-soft rfkill line/software rfkill line:
-
-        A rfkill line the wireless device driver can directly change the state
-        of.  Related to rfkill_state RFKILL_STATE_SOFT_BLOCKED.
-
-hard rfkill line/hardware rfkill line:
-
-        A rfkill line that works fully in hardware or firmware, and that cannot
-        be overridden by the kernel driver.  The hardware device or the
-        firmware just exports its status to the driver, but it is read-only.
-        Related to rfkill_state RFKILL_STATE_HARD_BLOCKED.
-
-The enum rfkill_state describes the rfkill state of a transmitter:
-
-When a rfkill line or rfkill controller is in the RFKILL_STATE_UNBLOCKED state,
-the wireless transmitter (radio TX circuit for example) is *enabled*.  When the
-it is in the RFKILL_STATE_SOFT_BLOCKED or RFKILL_STATE_HARD_BLOCKED, the
-wireless transmitter is to be *blocked* from operating.
-
-RFKILL_STATE_SOFT_BLOCKED indicates that a call to toggle_radio() can change
-that state.  RFKILL_STATE_HARD_BLOCKED indicates that a call to toggle_radio()
-will not be able to change the state and will return with a suitable error if
-attempts are made to set the state to RFKILL_STATE_UNBLOCKED.
-
-RFKILL_STATE_HARD_BLOCKED is used by drivers to signal that the device is
-locked in the BLOCKED state by a hardwire rfkill line (typically an input pin
-that, when active, forces the transmitter to be disabled) which the driver
-CANNOT override.
-
-Full rfkill functionality requires two different subsystems to cooperate: the
-input layer and the rfkill class.  The input layer issues *commands* to the
-entire system requesting that devices registered to the rfkill class change
-state.  The way this interaction happens is not complex, but it is not obvious
-either:
-
-Kernel Input layer:
-
-        * Generates KEY_WWAN, KEY_WLAN, KEY_BLUETOOTH, SW_RFKILL_ALL, and
-          other such events when the user presses certain keys, buttons, or
-          toggles certain physical switches.
-
-        THE INPUT LAYER IS NEVER USED TO PROPAGATE STATUS, NOTIFICATIONS OR THE
-        KIND OF STUFF AN ON-SCREEN-DISPLAY APPLICATION WOULD REPORT.  It is
-        used to issue *commands* for the system to change behaviour, and these
-        commands may or may not be carried out by some kernel driver or
-        userspace application.  It follows that doing user feedback based only
-        on input events is broken, as there is no guarantee that an input event
-        will be acted upon.
-
-        Most wireless communication device drivers implementing rfkill
-        functionality MUST NOT generate these events, and have no reason to
-        register themselves with the input layer.  Doing otherwise is a common
-        misconception.  There is an API to propagate rfkill status change
-        information, and it is NOT the input layer.
-
-rfkill class:
-
-        * Calls a hook in a driver to effectively change the wireless
-          transmitter state;
-        * Keeps track of the wireless transmitter state (with help from
-          the driver);
-        * Generates userspace notifications (uevents) and a call to a
-          notification chain (kernel) when there is a wireless transmitter
-          state change;
-        * Connects a wireless communications driver with the common rfkill
-          control system, which, for example, allows actions such as
-          "switch all bluetooth devices offline" to be carried out by
-          userspace or by rfkill-input.
-
-        THE RFKILL CLASS NEVER ISSUES INPUT EVENTS.  THE RFKILL CLASS DOES
-        NOT LISTEN TO INPUT EVENTS.  NO DRIVER USING THE RFKILL CLASS SHALL
-        EVER LISTEN TO, OR ACT ON RFKILL INPUT EVENTS.  Doing otherwise is
-        a layering violation.
-
-        Most wireless data communication drivers in the kernel have just to
-        implement the rfkill class API to work properly.  Interfacing to the
-        input layer is not often required (and is very often a *bug*) on
-        wireless drivers.
-
-        Platform drivers often have to attach to the input layer to *issue*
-        (but never to listen to) rfkill events for rfkill switches, and also to
-        the rfkill class to export a control interface for the platform rfkill
-        controllers to the rfkill subsystem.  This does NOT mean the rfkill
-        switch is attached to a rfkill class (doing so is almost always wrong).
-        It just means the same kernel module is the driver for different
-        devices (rfkill switches and rfkill controllers).
-
-
-Userspace input handlers (uevents) or kernel input handlers (rfkill-input):
-
-        * Implements the policy of what should happen when one of the input
-          layer events related to rfkill operation is received.
-        * Uses the sysfs interface (userspace) or private rfkill API calls
-          to tell the devices registered with the rfkill class to change
-          their state (i.e. translates the input layer event into real
-          action).
-
-        * rfkill-input implements EPO by handling EV_SW SW_RFKILL_ALL 0
-          (power off all transmitters) in a special way: it ignores any
-          overrides and local state cache and forces all transmitters to the
-          RFKILL_STATE_SOFT_BLOCKED state (including those which are already
-          supposed to be BLOCKED).
-        * rfkill EPO will remain active until rfkill-input receives an
-          EV_SW SW_RFKILL_ALL 1 event.  While the EPO is active, transmitters
-          are locked in the blocked state (rfkill will refuse to unblock them).
-        * rfkill-input implements different policies that the user can
-          select for handling EV_SW SW_RFKILL_ALL 1.  It will unlock rfkill,
-          and either do nothing (leave transmitters blocked, but now unlocked),
-          restore the transmitters to their state before the EPO, or unblock
-          them all.
-
-Userspace uevent handler or kernel platform-specific drivers hooked to the
-rfkill notifier chain:
-
-        * Taps into the rfkill notifier chain or to KOBJ_CHANGE uevents,
-          in order to know when a device that is registered with the rfkill
-          class changes state;
-        * Issues feedback notifications to the user;
-        * In the rare platforms where this is required, synthesizes an input
-          event to command all *OTHER* rfkill devices to also change their
-          statues when a specific rfkill device changes state.
-
-
-===============================================================================
-3: Kernel driver guidelines
-
-Remember: point-of-view is everything for a driver that connects to the rfkill
-subsystem.  All the details below must be measured/perceived from the point of
-view of the specific driver being modified.
-
-The first thing one needs to know is whether his driver should be talking to
-the rfkill class or to the input layer.  In rare cases (platform drivers), it
-could happen that you need to do both, as platform drivers often handle a
-variety of devices in the same driver.
-
-Do not mistake input devices for rfkill controllers.  The only type of "rfkill
-switch" device that is to be registered with the rfkill class are those
-directly controlling the circuits that cause a wireless transmitter to stop
-working (or the software equivalent of them), i.e. what we call a rfkill
-controller.  Every other kind of "rfkill switch" is just an input device and
-MUST NOT be registered with the rfkill class.
-
-A driver should register a device with the rfkill class when ALL of the
-following conditions are met (they define a rfkill controller):
-
-1. The device is/controls a data communications wireless transmitter;
-
-2. The kernel can interact with the hardware/firmware to CHANGE the wireless
-   transmitter state (block/unblock TX operation);
-
-3. The transmitter can be made to not emit any energy when "blocked":
-   rfkill is not about blocking data transmissions, it is about blocking
-   energy emission;
-
-A driver should register a device with the input subsystem to issue
-rfkill-related events (KEY_WLAN, KEY_BLUETOOTH, KEY_WWAN, KEY_WIMAX,
-SW_RFKILL_ALL, etc) when ALL of the folowing conditions are met:
-
-1. It is directly related to some physical device the user interacts with, to
-   command the O.S./firmware/hardware to enable/disable a data communications
-   wireless transmitter.
-
-   Examples of the physical device are: buttons, keys and switches the user
-   will press/touch/slide/switch to enable or disable the wireless
-   communication device.
-
-2. It is NOT slaved to another device, i.e. there is no other device that
-   issues rfkill-related input events in preference to this one.
-
-   Please refer to the corner cases and examples section for more details.
-
-When in doubt, do not issue input events.  For drivers that should generate
-input events in some platforms, but not in others (e.g. b43), the best solution
-is to NEVER generate input events in the first place.  That work should be
-deferred to a platform-specific kernel module (which will know when to generate
-events through the rfkill notifier chain) or to userspace.  This avoids the
-usual maintenance problems with DMI whitelisting.
-
-
-Corner cases and examples:
-====================================
-
-1. If the device is an input device that, because of hardware or firmware,
-causes wireless transmitters to be blocked regardless of the kernel's will, it
-is still just an input device, and NOT to be registered with the rfkill class.
-
-2. If the wireless transmitter switch control is read-only, it is an input
-device and not to be registered with the rfkill class (and maybe not to be made
-an input layer event source either, see below).
-
-3. If there is some other device driver *closer* to the actual hardware the
-user interacted with (the button/switch/key) to issue an input event, THAT is
-the device driver that should be issuing input events.
-
-E.g:
-  [RFKILL slider switch] -- [GPIO hardware] -- [WLAN card rf-kill input]
-                           (platform driver)    (wireless card driver)
-
-The user is closer to the RFKILL slide switch plaform driver, so the driver
-which must issue input events is the platform driver looking at the GPIO
-hardware, and NEVER the wireless card driver (which is just a slave).  It is
-very likely that there are other leaves than just the WLAN card rf-kill input
-(e.g. a bluetooth card, etc)...
-
-On the other hand, some embedded devices do this:
-
-  [RFKILL slider switch] -- [WLAN card rf-kill input]
-                             (wireless card driver)
-
-In this situation, the wireless card driver *could* register itself as an input
-device and issue rf-kill related input events... but in order to AVOID the need
-for DMI whitelisting, the wireless card driver does NOT do it.  Userspace (HAL)
-or a platform driver (that exists only on these embedded devices) will do the
-dirty job of issuing the input events.
-
-
-COMMON MISTAKES in kernel drivers, related to rfkill:
-====================================
-
-1. NEVER confuse input device keys and buttons with input device switches.
-
-  1a. Switches are always set or reset.  They report the current state
-      (on position or off position).
-
-  1b. Keys and buttons are either in the pressed or not-pressed state, and
-      that's it.  A "button" that latches down when you press it, and
-      unlatches when you press it again is in fact a switch as far as input
-      devices go.
-
-Add the SW_* events you need for switches, do NOT try to emulate a button using
-KEY_* events just because there is no such SW_* event yet.  Do NOT try to use,
-for example, KEY_BLUETOOTH when you should be using SW_BLUETOOTH instead.
-
-2. Input device switches (sources of EV_SW events) DO store their current state
-(so you *must* initialize it by issuing a gratuitous input layer event on
-driver start-up and also when resuming from sleep), and that state CAN be
-queried from userspace through IOCTLs.  There is no sysfs interface for this,
-but that doesn't mean you should break things trying to hook it to the rfkill
-class to get a sysfs interface :-)
-
-3. Do not issue *_RFKILL_ALL events by default, unless you are sure it is the
-correct event for your switch/button.  These events are emergency power-off
-events when they are trying to turn the transmitters off.  An example of an
-input device which SHOULD generate *_RFKILL_ALL events is the wireless-kill
-switch in a laptop which is NOT a hotkey, but a real sliding/rocker switch.
-An example of an input device which SHOULD NOT generate *_RFKILL_ALL events by
-default, is any sort of hot key that is type-specific (e.g. the one for WLAN).
-
-
-3.1 Guidelines for wireless device drivers
-------------------------------------------
-
-(in this text, rfkill->foo means the foo field of struct rfkill).
-
-1. Each independent transmitter in a wireless device (usually there is only one
-transmitter per device) should have a SINGLE rfkill class attached to it.
-
-2. If the device does not have any sort of hardware assistance to allow the
-driver to rfkill the device, the driver should emulate it by taking all actions
-required to silence the transmitter.
-
-3. If it is impossible to silence the transmitter (i.e. it still emits energy,
-even if it is just in brief pulses, when there is no data to transmit and there
-is no hardware support to turn it off) do NOT lie to the users.  Do not attach
-it to a rfkill class.  The rfkill subsystem does not deal with data
-transmission, it deals with energy emission.  If the transmitter is emitting
-energy, it is not blocked in rfkill terms.
-
-4. It doesn't matter if the device has multiple rfkill input lines affecting
-the same transmitter, their combined state is to be exported as a single state
-per transmitter (see rule 1).
-
-This rule exists because users of the rfkill subsystem expect to get (and set,
-when possible) the overall transmitter rfkill state, not of a particular rfkill
-line.
+The rfkill class is provided for kernel drivers to register their radio
+transmitter with the kernel, provide methods for turning it on and off and,
+optionally, letting the system know about hardware-disabled states that may
+be implemented on the device. This code is enabled with the CONFIG_RFKILL
+Kconfig option, which drivers can "select".
 
-5. The wireless device driver MUST NOT leave the transmitter enabled during
-suspend and hibernation unless:
+The rfkill class code also notifies userspace of state changes, this is
+achieved via uevents. It also provides some sysfs files for userspace to
+check the status of radio transmitters. See the "Userspace support" section
+below.
 
-        5.1. The transmitter has to be enabled for some sort of functionality
-        like wake-on-wireless-packet or autonomous packed forwarding in a mesh
-        network, and that functionality is enabled for this suspend/hibernation
-        cycle.
 
-AND
+The rfkill-input code implements a basic response to rfkill buttons -- it
+implements turning on/off all devices of a certain class (or all).
 
-        5.2. The device was not on a user-requested BLOCKED state before
-        the suspend (i.e. the driver must NOT unblock a device, not even
-        to support wake-on-wireless-packet or remain in the mesh).
+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 but drivers can well
+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 other words, there is absolutely no allowed scenario where a driver can
-automatically take action to unblock a rfkill controller (obviously, this deals
-with scenarios where soft-blocking or both soft and hard blocking is happening.
-Scenarios where hardware rfkill lines are the only ones blocking the
-transmitter are outside of this rule, since the wireless device driver does not
-control its input hardware rfkill lines in the first place).
 
-6. During resume, rfkill will try to restore its previous state.
+The entire functionality is spread over more than one subsystem:
 
-7. After a rfkill class is suspended, it will *not* call rfkill->toggle_radio
-until it is resumed.
+ * The kernel input layer generates KEY_WWAN, KEY_WLAN etc. and
+   SW_RFKILL_ALL -- when the user presses a button. Drivers for radio
+   transmitters generally do not register to the input layer, unless the
+   device really provides an input device (i.e. a button that has no
+   effect other than generating a button press event)
 
+ * The rfkill-input code hooks up to these events and switches the soft-block
+   of the various radio transmitters, depending on the button type.
 
-Example of a WLAN wireless driver connected to the rfkill subsystem:
---------------------------------------------------------------------
+ * The rfkill drivers turn off/on their transmitters as requested.
 
-A certain WLAN card has one input pin that causes it to block the transmitter
-and makes the status of that input pin available (only for reading!) to the
-kernel driver.  This is a hard rfkill input line (it cannot be overridden by
-the kernel driver).
+ * The rfkill class will generate userspace notifications (uevents) to tell
+   userspace what the current state is.
 
-The card also has one PCI register that, if manipulated by the driver, causes
-it to block the transmitter.  This is a soft rfkill input line.
 
-It has also a thermal protection circuitry that shuts down its transmitter if
-the card overheats, and makes the status of that protection available (only for
-reading!) to the kernel driver.  This is also a hard rfkill input line.
 
-If either one of these rfkill lines are active, the transmitter is blocked by
-the hardware and forced offline.
+3. Kernel driver guidelines
 
-The driver should allocate and attach to its struct device *ONE* instance of
-the rfkill class (there is only one transmitter).
 
-It can implement the get_state() hook, and return RFKILL_STATE_HARD_BLOCKED if
-either one of its two hard rfkill input lines are active.  If the two hard
-rfkill lines are inactive, it must return RFKILL_STATE_SOFT_BLOCKED if its soft
-rfkill input line is active.  Only if none of the rfkill input lines are
-active, will it return RFKILL_STATE_UNBLOCKED.
+Drivers for radio transmitters normally implement only the rfkill class.
+These drivers may not unblock the transmitter based on own decisions, they
+should act on information provided by the rfkill class only.
 
-Since the device has a hardware rfkill line, it IS subject to state changes
-external to rfkill.  Therefore, the driver must make sure that it calls
-rfkill_force_state() to keep the status always up-to-date, and it must do a
-rfkill_force_state() on resume from sleep.
+Platform drivers might implement input devices if the rfkill button is just
+that, a button. If that button influences the hardware then you need to
+implement an rfkill class instead. This also applies if the platform provides
+a way to turn on/off the transmitter(s).
 
-Every time the driver gets a notification from the card that one of its rfkill
-lines changed state (polling might be needed on badly designed cards that don't
-generate interrupts for such events), it recomputes the rfkill state as per
-above, and calls rfkill_force_state() to update it.
+During suspend/hibernation, transmitters should only be left enabled when
+wake-on wlan or similar functionality requires it and the device wasn't
+blocked before suspend/hibernate. Note that it may be necessary to update
+the rfkill subsystem's idea of what the current state is at resume time if
+the state may have changed over suspend.
 
-The driver should implement the toggle_radio() hook, that:
 
-1. Returns an error if one of the hardware rfkill lines are active, and the
-caller asked for RFKILL_STATE_UNBLOCKED.
 
-2. Activates the soft rfkill line if the caller asked for state
-RFKILL_STATE_SOFT_BLOCKED.  It should do this even if one of the hard rfkill
-lines are active, effectively double-blocking the transmitter.
-
-3. Deactivates the soft rfkill line if none of the hardware rfkill lines are
-active and the caller asked for RFKILL_STATE_UNBLOCKED.
-
-===============================================================================
-4: Kernel API
+4. Kernel API
 
 To build a driver with rfkill subsystem support, the driver should depend on
-(or select) the Kconfig symbol RFKILL; it should _not_ depend on RKFILL_INPUT.
+(or select) the Kconfig symbol RFKILL.
 
 The hardware the driver talks to may be write-only (where the current state
 of the hardware is unknown), or read-write (where the hardware can be queried
 about its current state).
 
-The rfkill class will call the get_state hook of a device every time it needs
-to know the *real* current state of the hardware.  This can happen often, but
-it does not do any polling, so it is not enough on hardware that is subject
-to state changes outside of the rfkill subsystem.
-
-Therefore, calling rfkill_force_state() when a state change happens is
-mandatory when the device has a hardware rfkill line, or when something else
-like the firmware could cause its state to be changed without going through the
-rfkill class.
-
-Some hardware provides events when its status changes.  In these cases, it is
-best for the driver to not provide a get_state hook, and instead register the
-rfkill class *already* with the correct status, and keep it updated using
-rfkill_force_state() when it gets an event from the hardware.
-
-rfkill_force_state() must be used on the device resume handlers to update the
-rfkill status, should there be any chance of the device status changing during
-the sleep.
-
-There is no provision for a statically-allocated rfkill struct.  You must
-use rfkill_allocate() to allocate one.
-
-You should:
-        - rfkill_allocate()
-        - modify rfkill fields (flags, name)
-        - modify state to the current hardware state (THIS IS THE ONLY TIME
-          YOU CAN ACCESS state DIRECTLY)
-        - rfkill_register()
+Calling rfkill_set_hw_state() when a state change happens is required from
+rfkill drivers that control devices that can be hard-blocked unless they also
+assign the poll_hw_block() callback (then the rfkill core will poll the
+device). Don't do this unless you cannot get the event in any other way.
 
-The only way to set a device to the RFKILL_STATE_HARD_BLOCKED state is through
-a suitable return of get_state() or through rfkill_force_state().
 
-When a device is in the RFKILL_STATE_HARD_BLOCKED state, the only way to switch
-it to a different state is through a suitable return of get_state() or through
-rfkill_force_state().
 
-If toggle_radio() is called to set a device to state RFKILL_STATE_SOFT_BLOCKED
-when that device is already at the RFKILL_STATE_HARD_BLOCKED state, it should
-not return an error.  Instead, it should try to double-block the transmitter,
-so that its state will change from RFKILL_STATE_HARD_BLOCKED to
-RFKILL_STATE_SOFT_BLOCKED should the hardware blocking cease.
-
-Please refer to the source for more documentation.
-
-===============================================================================
-5: Userspace support
-
-rfkill devices issue uevents (with an action of "change"), with the following
-environment variables set:
-
-RFKILL_NAME
-RFKILL_STATE
-RFKILL_TYPE
+5. Userspace support
 
-The ABI for these variables is defined by the sysfs attributes.  It is best
-to take a quick look at the source to make sure of the possible values.
-
-It is expected that HAL will trap those, and bridge them to DBUS, etc.  These
-events CAN and SHOULD be used to give feedback to the user about the rfkill
-status of the system.
-
-Input devices may issue events that are related to rfkill.  These are the
-various KEY_* events and SW_* events supported by rfkill-input.c.
-
-Userspace may not change the state of an rfkill switch in response to an
-input event, it should refrain from changing states entirely.
-
-Userspace cannot assume it is the only source of control for rfkill switches.
-Their state can change due to firmware actions, direct user actions, and the
-rfkill-input EPO override for *_RFKILL_ALL.
-
-When rfkill-input is not active, userspace must initiate a rfkill status
-change by writing to the "state" attribute in order for anything to happen.
-
-Take particular care to implement EV_SW SW_RFKILL_ALL properly.  When that
-switch is set to OFF, *every* rfkill device *MUST* be immediately put into the
-RFKILL_STATE_SOFT_BLOCKED state, no questions asked.
-
-The following sysfs entries will be created:
+The following sysfs entries exist for every rfkill device:
 
         name: Name assigned by driver to this key (interface or driver name).
         type: Name of the key type ("wlan", "bluetooth", etc).
         state: Current state of the transmitter
                 0: RFKILL_STATE_SOFT_BLOCKED
-                        transmitter is forced off, but one can override it
-                        by a write to the state attribute;
+                        transmitter is turned off by software
                 1: RFKILL_STATE_UNBLOCKED
-                        transmiter is NOT forced off, and may operate if
-                        all other conditions for such operation are met
-                        (such as interface is up and configured, etc);
+                        transmiter is (potentially) active
                 2: RFKILL_STATE_HARD_BLOCKED
                         transmitter is forced off by something outside of
-                        the driver's control.  One cannot set a device to
-                        this state through writes to the state attribute;
-        claim: 1: Userspace handles events, 0: Kernel handles events
-
-Both the "state" and "claim" entries are also writable. For the "state" entry
-this means that when 1 or 0 is written, the device rfkill state (if not yet in
-the requested state), will be will be toggled accordingly.
-
-For the "claim" entry writing 1 to it means that the kernel no longer handles
-key events even though RFKILL_INPUT input was enabled. When "claim" has been
-set to 0, userspace should make sure that it listens for the input events or
-check the sysfs "state" entry regularly to correctly perform the required tasks
-when the rkfill key is pressed.
-
-A note about input devices and EV_SW events:
-
-In order to know the current state of an input device switch (like
-SW_RFKILL_ALL), you will need to use an IOCTL.  That information is not
-available through sysfs in a generic way at this time, and it is not available
-through the rfkill class AT ALL.
+                        the driver's control.
+        claim: 0: Kernel handles events (currently always reads that value)
+
+rfkill devices also issue uevents (with an action of "change"), with the
+following environment variables set:
+
+RFKILL_NAME
+RFKILL_STATE
+RFKILL_TYPE
+
+The contents of these variables corresponds to the "name", "state" and
+"type" sysfs files explained above.