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dac24ab396
Add a documentation file which contains a short description about rfkill with some notes about drivers and the userspace interface. Changes since v1 and v2: - Spellchecking Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com> Acked-by: Dmitry Torokhov <dtor@mail.ru> Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
90 lines
3.5 KiB
Plaintext
90 lines
3.5 KiB
Plaintext
rfkill - RF switch subsystem support
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====================================
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1 Implementation details
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2 Driver support
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3 Userspace support
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===============================================================================
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1: Implementation details
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The rfkill switch subsystem offers support for keys often found on laptops
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to enable wireless devices like WiFi and Bluetooth.
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This is done by providing the user 3 possibilities:
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1 - The rfkill system handles all events; userspace is not aware of events.
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2 - The rfkill system handles all events; userspace is informed about the events.
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3 - The rfkill system does not handle events; userspace handles all events.
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The buttons to enable and disable the wireless radios are important in
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situations where the user is for example using his laptop on a location where
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wireless radios _must_ be disabled (e.g. airplanes).
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Because of this requirement, userspace support for the keys should not be
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made mandatory. Because userspace might want to perform some additional smarter
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tasks when the key is pressed, rfkill still provides userspace the possibility
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to take over the task to handle the key events.
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The system inside the kernel has been split into 2 separate sections:
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1 - RFKILL
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2 - RFKILL_INPUT
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The first option enables rfkill support and will make sure userspace will
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be notified of any events through the input device. It also creates several
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sysfs entries which can be used by userspace. See section "Userspace support".
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The second option provides an rfkill input handler. This handler will
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listen to all rfkill key events and will toggle the radio accordingly.
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With this option enabled userspace could either do nothing or simply
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perform monitoring tasks.
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====================================
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2: Driver support
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To build a driver with rfkill subsystem support, the driver should
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depend on the Kconfig symbol RFKILL; it should _not_ depend on
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RKFILL_INPUT.
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Unless key events trigger an interrupt to which the driver listens, polling
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will be required to determine the key state changes. For this the input
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layer providers the input-polldev handler.
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A driver should implement a few steps to correctly make use of the
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rfkill subsystem. First for non-polling drivers:
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- rfkill_allocate()
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- input_allocate_device()
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- rfkill_register()
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- input_register_device()
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For polling drivers:
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- rfkill_allocate()
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- input_allocate_polled_device()
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- rfkill_register()
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- input_register_polled_device()
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When a key event has been detected, the correct event should be
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sent over the input device which has been registered by the driver.
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====================================
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3: Userspace support
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For each key an input device will be created which will send out the correct
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key event when the rfkill key has been pressed.
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The following sysfs entries will be created:
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name: Name assigned by driver to this key (interface or driver name).
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type: Name of the key type ("wlan", "bluetooth", etc).
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state: Current state of the key. 1: On, 0: Off.
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claim: 1: Userspace handles events, 0: Kernel handles events
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Both the "state" and "claim" entries are also writable. For the "state" entry
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this means that when 1 or 0 is written all radios, not yet in the requested
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state, will be will be toggled accordingly.
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For the "claim" entry writing 1 to it means that the kernel no longer handles
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key events even though RFKILL_INPUT input was enabled. When "claim" has been
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set to 0, userspace should make sure that it listens for the input events or
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check the sysfs "state" entry regularly to correctly perform the required
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tasks when the rkfill key is pressed.
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