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Diffstat (limited to 'Documentation/rfkill.txt')
| -rw-r--r-- | Documentation/rfkill.txt | 137 |
1 files changed, 69 insertions, 68 deletions
diff --git a/Documentation/rfkill.txt b/Documentation/rfkill.txt index 1b74b5f30af4..c8acd8659e91 100644 --- a/Documentation/rfkill.txt +++ b/Documentation/rfkill.txt @@ -3,9 +3,8 @@ rfkill - RF kill switch support 1. Introduction 2. Implementation details -3. Kernel driver guidelines -4. Kernel API -5. Userspace support +3. Kernel API +4. Userspace support 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 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 -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 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". - -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. +The rfkill subsystem is composed of three main components: + * the rfkill core, + * the deprecated rfkill-input module (an input layer handler, being + replaced by userspace policy code) and + * the rfkill drivers. +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. -The rfkill-input code implements a basic response to rfkill buttons -- it -implements turning on/off all devices of a certain class (or all). +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. 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(). - - -The entire functionality is spread over more than one subsystem: - - * 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. +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. +3. Kernel API -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. +Drivers for radio transmitters normally implement an rfkill driver. 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 +implement an rfkill driver instead. This also applies if the platform provides a way to turn on/off the transmitter(s). -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. - +For some platforms, it is possible that the hardware state changes during +suspend/hibernation, in which case it will be necessary to update the rfkill +core with the current state is at resume time. +To create an rfkill driver, driver's Kconfig needs to have -4. Kernel API + depends on RFKILL || !RFKILL -To build a driver with rfkill subsystem support, the driver should depend on -(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). +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 +case all rfkill API can still be used but will be provided by static inlines +which compile to almost nothing. 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 @@ -105,10 +84,33 @@ device). Don't do this unless you cannot get the event in any other way. 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). - type: Name of the key type ("wlan", "bluetooth", etc). + type: Driver type string ("wlan", "bluetooth", etc). state: Current state of the transmitter 0: RFKILL_STATE_SOFT_BLOCKED transmitter is turned off by software @@ -117,7 +119,12 @@ The following sysfs entries exist for every rfkill device: 2: RFKILL_STATE_HARD_BLOCKED transmitter is forced off by something outside of 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 following environment variables set: @@ -128,9 +135,3 @@ RFKILL_TYPE The contents of these variables corresponds to the "name", "state" and "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. |
