8c27ceff36
The previous patch renamed several files that are cross-referenced along the Kernel documentation. Adjust the links to point to the right places. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
125 lines
5 KiB
Text
125 lines
5 KiB
Text
rfkill - RF kill switch support
|
|
===============================
|
|
|
|
1. Introduction
|
|
2. Implementation details
|
|
3. Kernel API
|
|
4. Userspace support
|
|
|
|
|
|
1. Introduction
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
|
|
2. 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.
|
|
|
|
|
|
3. 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 is 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, 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).
|
|
|
|
|
|
5. 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 either 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 contents of these variables corresponds to the "name", "state" and
|
|
"type" sysfs files explained above.
|
|
|
|
|
|
For further details consult Documentation/ABI/stable/sysfs-class-rfkill.
|