linux-kernel - Re: [PATCH 4/8] rfkill: add read-write rfkill switch support

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Date:	Sat, 12 Apr 2008 12:36:43 +0200
From:	Ivo van Doorn <ivdoorn@...il.com>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	linux-kernel@...r.kernel.org,
	"John W. Linville" <linville@...driver.com>,
	Dmitry Torokhov <dtor@...l.ru>
Subject: Re: [PATCH 4/8] rfkill: add read-write rfkill switch support

Hi,

> Currently, rfkill supports only write-only rfkill switches.  There is no
> provision for querying the current switch state from the hardware/firmware.

No that is by design, the input_polled_dev interface is there for polling.

> This is bad on hardware where the switch state can change behind the
> kernel's back (which is rather common).  There is no reason to keep kernel
> state incorrect, when we have the possibility to match reality.
> 
> There is also the issue of read-only rfkill switches (support to be added
> in a later patch), which absolutely requires support to read the current
> state from the hardware in order to be implemented.

See rt2x00 and b43 in driver-wireless for an example implementation
of pollable input device and rfkill

> In order to implement the read/write functionality:
> 
> Add a get_state() hook that is called by the class every time it needs to
> fetch the current state of the switch.  Add a call to this hook every time
> the *current* state of the radio plays a role in a decision.
> 
> Also add a force_state() method that can be used to forcefully syncronize
> the class' idea of the current state of the switch.  This allows for a
> faster implementation of the read/write functionality, as a driver which
> get events on switch changes can avoid the need for a get_state() hook.
> 
> If the get_state() hook is left as NULL, current behaviour is maintained,
> so this change is fully backwards compatible with the current rfkill
> drivers.
> 
> If the firmware is event driven, leave get_state() NULL in the driver, set
> the initial state properly before registering the rfkill class, and use the
> force_state() method in the driver to keep the class up-to-date.
> 
> get_state() can be called by the class from atomic context. It must not
> sleep.
> 
> Signed-off-by: Henrique de Moraes Holschuh <hmh@....eng.br>
> Cc: Ivo van Doorn <IvDoorn@...il.com>
> Cc: John W. Linville <linville@...driver.com>
> Cc: Dmitry Torokhov <dtor@...l.ru>

I'm going to NACK this patch.

Ivo
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