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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/driver-api/rfkill.rst | |
parent | Initial commit. (diff) | |
download | linux-430c2fc249ea5c0536abd21c23382884005c9093.tar.xz linux-430c2fc249ea5c0536abd21c23382884005c9093.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/driver-api/rfkill.rst')
-rw-r--r-- | Documentation/driver-api/rfkill.rst | 132 |
1 files changed, 132 insertions, 0 deletions
diff --git a/Documentation/driver-api/rfkill.rst b/Documentation/driver-api/rfkill.rst new file mode 100644 index 000000000..7d3684e81 --- /dev/null +++ b/Documentation/driver-api/rfkill.rst @@ -0,0 +1,132 @@ +=============================== +rfkill - RF kill switch support +=============================== + + +.. contents:: + :depth: 2 + +Introduction +============ + +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. + +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 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 overridden by software + + - soft block + writable radio block (need not be readable) that is set by + the system software. + +The rfkill subsystem has two parameters, rfkill.default_state and +rfkill.master_switch_mode, which are documented in +admin-guide/kernel-parameters.rst. + + +Implementation details +====================== + +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 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 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. + + +Kernel API +========== + +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 driver instead. This also applies if the platform provides +a way to turn on/off the transmitter(s). + +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 at resume time. + +To create an rfkill driver, driver's Kconfig needs to have:: + + depends on RFKILL || !RFKILL + +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, in 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 +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. + +rfkill provides per-switch LED triggers, which can be used to drive LEDs +according to the switch state (LED_FULL when blocked, LED_OFF otherwise). + + +Userspace support +================= + +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. Changes can be obtained by either polling the descriptor for +hotplug or state change events or by listening for uevents emitted by the +rfkill core framework. + +Additionally, each rfkill device is registered in sysfs and emits uevents. + +rfkill devices issue uevents (with an action of "change"), with the following +environment variables set:: + + RFKILL_NAME + RFKILL_STATE + RFKILL_TYPE + +The content of these variables corresponds to the "name", "state" and +"type" sysfs files explained above. + +For further details consult Documentation/ABI/stable/sysfs-class-rfkill. |