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rfkill: document rfkill_force_state as required (v2) 

While the rfkill class does work with just get_state(), it doesn't work
well on devices that are subject to external events that cause rfkill state
changes.

Document that rfkill_force_state() is required in those cases.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
This commit is contained in:
Henrique de Moraes Holschuh 2008-07-21 21:18:17 -03:00 committed by John W. Linville
parent 734b5aa911
commit 2fd9b2212e
2 changed files with 22 additions and 5 deletions
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20
Documentation/rfkill.txt
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@ -390,9 +390,10 @@ rfkill lines are inactive, it must return RFKILL_STATE_SOFT_BLOCKED if its soft
rfkill input line is active. Only if none of the rfkill input lines are
active, will it return RFKILL_STATE_UNBLOCKED.
If it doesn't implement the get_state() hook, it must make sure that its calls
to rfkill_force_state() are enough to keep the status always up-to-date, and it
must do a rfkill_force_state() on resume from sleep.
Since the device has a hardware rfkill line, it IS subject to state changes
external to rfkill. Therefore, the driver must make sure that it calls
rfkill_force_state() to keep the status always up-to-date, and it must do a
rfkill_force_state() on resume from sleep.
Every time the driver gets a notification from the card that one of its rfkill
lines changed state (polling might be needed on badly designed cards that don't
@ -422,13 +423,24 @@ of the hardware is unknown), or read-write (where the hardware can be queried
about its current state).
The rfkill class will call the get_state hook of a device every time it needs
to know the *real* current state of the hardware. This can happen often.
to know the *real* current state of the hardware. This can happen often, but
it does not do any polling, so it is not enough on hardware that is subject
to state changes outside of the rfkill subsystem.
Therefore, calling rfkill_force_state() when a state change happens is
mandatory when the device has a hardware rfkill line, or when something else
like the firmware could cause its state to be changed without going through the
rfkill class.
Some hardware provides events when its status changes. In these cases, it is
best for the driver to not provide a get_state hook, and instead register the
rfkill class *already* with the correct status, and keep it updated using
rfkill_force_state() when it gets an event from the hardware.
rfkill_force_state() must be used on the device resume handlers to update the
rfkill status, should there be any chance of the device status changing during
the sleep.
There is no provision for a statically-allocated rfkill struct. You must
use rfkill_allocate() to allocate one.

7
net/rfkill/rfkill.c
View File

@ -252,7 +252,12 @@ EXPORT_SYMBOL_GPL(rfkill_epo);
* a notification by the firmware/hardware of the current *real*
* state of the radio rfkill switch.
*
* It may not be called from an atomic context.
* Devices which are subject to external changes on their rfkill
* state (such as those caused by a hardware rfkill line) MUST
* have their driver arrange to call rfkill_force_state() as soon
* as possible after such a change.
*
* This function may not be called from an atomic context.
*/
int rfkill_force_state(struct rfkill *rfkill, enum rfkill_state state)
{