Subject: Re: [RFC] rfkill - Add support for input key to control wireless
	radio
From: Dan Williams <dcbw@redhat.com>
To: Ivo van Doorn <ivdoorn@gmail.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>, linux-kernel@vger.kernel.org,
       netdev@vger.kernel.org, John Linville <linville@tuxdriver.com>,
       Jiri Benc <jbenc@suse.cz>, Lennart Poettering <lennart@poettering.net>,
       Johannes Berg <johannes@sipsolutions.net>,
       Larry Finger <Larry.Finger@lwfinger.net>
In-Reply-To: <200612062241.58476.IvDoorn@gmail.com>
References: <200612031936.34343.IvDoorn@gmail.com>
	 <200612062031.57148.IvDoorn@gmail.com>
	 <d120d5000612061218x4eac87e0jc18409f82bb7c99c@mail.gmail.com>
	 <200612062241.58476.IvDoorn@gmail.com>
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Date: Thu, 07 Dec 2006 08:22:34 -0500
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On Wed, 2006-12-06 at 22:41 +0100, Ivo van Doorn wrote:
> Hi,
> 
> > > > That is my point. Given the fact that there are keys that are not
> > > > directly connected with the radio switch userspace will have to handle
> > > > them (wait for events then turn off radios somehow). You are
> > > > advocating that userspace should also implement 2nd method for buttons
> > > > that belong to rfkill interface. I do not understand the need for 2nd
> > > > interface. If you separate radio switch from button code then
> > > > userspace only need to implement 1st interface and be done with it.
> > > > You will have set of cards that provide interface to enable/disable
> > > > their transmitters and set of buttons that signal userspace desired
> > > > state change. If both switch and button is implemented by the same
> > > > driver then the driver can implement automatic button handling.
> > > > Otherwise userspace help is necessary.
> > >
> > > Well there are 3 possible hardware key approaches:
> > >
> > >  1 - Hardware key that controls the hardware radio, and does not report anything to userspace
> > 
> > Can't do anything here so just ignore it.
> 
> Ok.
> 
> > >  2 - Hardware key that does not control the hardware radio and does not report anything to userspace
> > 
> > Kind of uninteresting button ;)
> 
> And this is the button that rfkill was originally designed for.
> Laptops with integrated WiFi cards from Ralink have a hardware button that don't send anything to
> userspace (unless the ACPI event is read) and does not directly control the radio itself.

My take: if there is a button on your keyboard or laptop labeled "Kill
my radio now", it _NEEDS_ to be somehow communicated to userspace what
happened when the user just pressed it a second ago.  Personally, I
don't particularly care how that happens, and I don't particularly care
what the driver does.  But if the driver, or the hardware, decides that
the button press means turning off the transmitter on whatever device
that button is for, a tool like NetworkManager needs to know this
somehow.  Ideally, this would be a HAL event, and HAL would get it from
somewhere.

The current situation with NM is unacceptable, and I can't do anything
about it because there is no standard interface for determining whether
the wireless card was disabled/enabled via rfkill.  I simply refuse to
code solutions to every vendor's rfkill mechanism (for ipw, reading
iwpriv or sysfs, for example).  I don't care how HAL gets the event, but
when HAL gets the event, it needs to broadcast it and NM needs to tear
down the connection and release the device.

That means (a) an event gets sent to userspace in some way that HAL can
read it, and (b) the event is clearly associated with specific piece[s]
of hardware on your system.  If HAL can't easily figure out what device
the event is for, then the event is also useless to both HAL and
NetworkManager and whatever else might use it.

Again, I don't care how that happens, but I like the fact that there's
renewed interest in getting this fixed.

Dan

> > >  3 - Hardware key that does not control the hardware radio and reports the key to userspace
> > >
> > > So rfkill should not be used in the case of (1) and (3), but we still need something to support (2)
> > > or should the keys not be handled by userspace and always by the driver?
> > > This is making rfkill moving slowly away from the generic approach for all rfkill keys as the initial
> > > intention was.
> > >
> > 
> > I my "vision" rfkill would represent userspace namageable radio
> > switch. We have the followng possible configurations:
> > 
> > 1. A device that does not allow controlling its transmitter from
> > userspace. The driver should not use/register with rfkill subsystem as
> > userspace can't do anyhting with it. If device has a button killing
> > the transmitter the driver can still signal userspace appropriate
> > event (KEY_WIFI, KEY_BLUETOOTH, etc) if it can detect that button was
> > presssed so userspace can monitor state of the transmitter and
> > probably shut down other transmitters to keep everything in sync.
> 
> And this event should be reported by a generic approach right? So it should
> be similar as with your point 2 below. But this would mean that the driver
> should create the input device. Or can a driver send the KEY_WIFI event
> over a main layer without the need of a personal input device?
> I am not that familiar with the input device layer in the kernel, and this is
> my first attempt on creating something for it, so I might have missed something. ;)
> 
> Because it could still register with rfkill, only not give the callback functions
> for changing the radio or polling. Then the driver can use the send_event function
> to inform rfkill of the event and process it further. The sysfs attributes could
> even be reduced to only add the change_status attribute when the radio_enable
> and radio_disable callback functions are implemented.
> 
> > 2. A device that does allow controlling its transmitter. The driver
> > may (should) register with rfkill subsystem. Additionally, if there is
> > a button, the driver should register it with input subsystem. Driver
> > should manage transmitter state in response to button presses unless
> > userspace takes over the process.
> 
> This is indeed the main goal of rfkill. :)
> 
> > 3. A device without transmitter but with a button - just register with
> > input core. Userspace will have to manage state of other devices with
> > transmitters in response to button presses.
> 
> This is clear too. Rfkill is only intended for drivers that control a device with
> a transmitter (WiFi, Bluetooth, IRDA) that have a button that is intended to
> do something with the radio/transmitter.
> 
> > Does this make sense?
> 
> Yes, this was what I intended to do with rfkill, so at that point we have
> the same goal.
> 
> > > > > > attribute should be a tri-state on/off/auto, "auto" meaning the driver
> > > > > > itself manages radio state. This would avoid another tacky IMHO point
> > > > > > that in your implementation mere opening of an input device takes over
> > > > > > RF driver. Explicit control allow applications "snoop" RF state
> > > > > > without disturbing it.
> > > > >
> > > > > Currently userspace can always check the state of the button whenever
> > > > > they like by checking the sysfs entry.
> > > > >
> > > >
> > > > Unless the key is not directly connected to the driver (so there is no
> > > > sysfs entry). Again you force 2 different interfaces.
> > >
> > > Ok, so input device opening should not block the rfkill signal and the rfkill handler
> > > should still go through with its work unless a different config option indicates that
> > > userspace wants to handle the event.
> > >
> > 
> > I don't think a config option is a good idea unless by config option
> > you mean a sysfs attribute.
> 
> I indeed meant a sysfs attribute. I should have been more clear on this. :)
> 
> Ivo
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