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rfkill: improve docs

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Now that the dust has settled a bit, improve the docs on rfkill
and include more information about /dev/rfkill.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
This commit is contained in:
Johannes Berg
2009-06-15 15:36:38 +02:00
committed by John W. Linville
parent 7e9debe978
commit ce0879e324
1 changed files with 69 additions and 68 deletions
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137
Documentation/rfkill.txt
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@@ -3,9 +3,8 @@ rfkill - RF kill switch support
1. Introduction 1. Introduction
2. Implementation details 2. Implementation details
3. Kernel driver guidelines 3. Kernel API
4. Kernel API 4. Userspace support
5. Userspace support
1. Introduction 1. Introduction
@@ -19,82 +18,62 @@ disable all transmitters of a certain type (or all). This is intended for
situations where transmitters need to be turned off, for example on situations where transmitters need to be turned off, for example on
aircraft. aircraft.
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:
- hard block: read-only radio block that cannot be overriden by software
- soft block: writable radio block (need not be readable) that is set by
the system software.
2. Implementation details 2. Implementation details
The rfkill subsystem is composed of various components: the rfkill class, the The rfkill subsystem is composed of three main components:
rfkill-input module (an input layer handler), and some specific input layer * the rfkill core,
events. * the deprecated rfkill-input module (an input layer handler, being
replaced by userspace policy code) and
* the rfkill drivers.
The rfkill class is provided for kernel drivers to register their radio The rfkill core provides API for kernel drivers to register their radio
transmitter with the kernel, provide methods for turning it on and off and, transmitter with the kernel, methods for turning it on and off and, letting
optionally, letting the system know about hardware-disabled states that may the system know about hardware-disabled states that may be implemented on
be implemented on the device. This code is enabled with the CONFIG_RFKILL the device.
Kconfig option, which drivers can "select".
The rfkill class code also notifies userspace of state changes, this is The rfkill core code also notifies userspace of state changes, and provides
achieved via uevents. It also provides some sysfs files for userspace to ways for userspace to query the current states. See the "Userspace support"
check the status of radio transmitters. See the "Userspace support" section section below.
below.
The rfkill-input code implements a basic response to rfkill buttons -- it
implements turning on/off all devices of a certain class (or all).
When the device is hard-blocked (either by a call to rfkill_set_hw_state() 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 or from query_hw_block) set_block() will be invoked for additional software
ignore the method call since they can use the return value of the function block, but drivers can ignore the method call since they can use the return
rfkill_set_hw_state() to sync the software state instead of keeping track value of the function rfkill_set_hw_state() to sync the software state
of calls to set_block(). 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.
The entire functionality is spread over more than one subsystem: 3. Kernel API
* 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.
* The rfkill drivers turn off/on their transmitters as requested.
* The rfkill class will generate userspace notifications (uevents) to tell
userspace what the current state is.
Drivers for radio transmitters normally implement an rfkill driver.
3. Kernel driver guidelines
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.
Platform drivers might implement input devices if the rfkill button is just 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 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 implement an rfkill driver instead. This also applies if the platform provides
a way to turn on/off the transmitter(s). a way to turn on/off the transmitter(s).
During suspend/hibernation, transmitters should only be left enabled when For some platforms, it is possible that the hardware state changes during
wake-on wlan or similar functionality requires it and the device wasn't suspend/hibernation, in which case it will be necessary to update the rfkill
blocked before suspend/hibernate. Note that it may be necessary to update core with the current state is at resume time.
the rfkill subsystem's idea of what the current state is at resume time if
the state may have changed over suspend.
To create an rfkill driver, driver's Kconfig needs to have
depends on RFKILL || !RFKILL
4. Kernel API to ensure the driver cannot be built-in when rfkill is modular. The !RFKILL
case allows the driver to be built when rfkill is not configured, which which
To build a driver with rfkill subsystem support, the driver should depend on case all rfkill API can still be used but will be provided by static inlines
(or select) the Kconfig symbol RFKILL. which compile to almost nothing.
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).
Calling rfkill_set_hw_state() when a state change happens is required from 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 rfkill drivers that control devices that can be hard-blocked unless they also
@@ -105,10 +84,33 @@ device). Don't do this unless you cannot get the event in any other way.
5. Userspace support 5. Userspace support
The following sysfs entries exist for every rfkill device: The recommended userspace interface to use is /dev/rfkill, which is a misc
character device that allows userspace to obtain and set the state of rfkill
devices and sets of devices. It also notifies userspace about device addition
and removal. The API is a simple read/write API that is defined in
linux/rfkill.h, with one ioctl that allows turning off the deprecated input
handler in the kernel for the transition period.
Except for the one ioctl, communication with the kernel is done via read()
and write() of instances of 'struct rfkill_event'. In this structure, the
soft and hard block are properly separated (unlike sysfs, see below) and
userspace is able to get a consistent snapshot of all rfkill devices in the
system. Also, it is possible to switch all rfkill drivers (or all drivers of
a specified type) into a state which also updates the default state for
hotplugged devices.
After an application opens /dev/rfkill, it can read the current state of
all devices, and afterwards can poll the descriptor for hotplug or state
change events.
Applications must ignore operations (the "op" field) they do not handle,
this allows the API to be extended in the future.
Additionally, each rfkill device is registered in sysfs and there has the
following attributes:
name: Name assigned by driver to this key (interface or driver name). name: Name assigned by driver to this key (interface or driver name).
type: Name of the key type ("wlan", "bluetooth", etc). type: Driver type string ("wlan", "bluetooth", etc).
state: Current state of the transmitter state: Current state of the transmitter
0: RFKILL_STATE_SOFT_BLOCKED 0: RFKILL_STATE_SOFT_BLOCKED
transmitter is turned off by software transmitter is turned off by software
@@ -117,7 +119,12 @@ The following sysfs entries exist for every rfkill device:
2: RFKILL_STATE_HARD_BLOCKED 2: RFKILL_STATE_HARD_BLOCKED
transmitter is forced off by something outside of transmitter is forced off by something outside of
the driver's control. the driver's control.
claim: 0: Kernel handles events (currently always reads that value) This file is deprecated because it can only properly show
three of the four possible states, soft-and-hard-blocked is
missing.
claim: 0: Kernel handles events
This file is deprecated because there no longer is a way to
claim just control over a single rfkill instance.
rfkill devices also issue uevents (with an action of "change"), with the rfkill devices also issue uevents (with an action of "change"), with the
following environment variables set: following environment variables set:
@@ -128,9 +135,3 @@ RFKILL_TYPE
The contents of these variables corresponds to the "name", "state" and The contents of these variables corresponds to the "name", "state" and
"type" sysfs files explained above. "type" sysfs files explained above.
An alternative userspace interface exists as a misc device /dev/rfkill,
which allows userspace to obtain and set the state of rfkill devices and
sets of devices. It also notifies userspace about device addition and
removal. The API is a simple read/write API that is defined in
linux/rfkill.h.