linux-kernel - Re: [PATCH v2 1/3] platform: x86: dell-rbtn: Dell Airplane Mode Switch driver

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Date:	Wed, 29 Apr 2015 20:59:26 +0200
From:	Pali Rohár <pali.rohar@...il.com>
To:	Gabriele Mazzotta <gabriele.mzt@...il.com>,
	Alex Hung <alex.hung@...onical.com>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	Darren Hart <dvhart@...radead.org>,
	platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] platform: x86: dell-rbtn: Dell Airplane Mode Switch driver

On Wednesday 29 April 2015 20:41:38 Gabriele Mazzotta wrote:
> On Wednesday 29 April 2015 20:16:06 Pali Rohár wrote:
> > On Wednesday 29 April 2015 20:11:38 Gabriele Mazzotta wrote:
> > > On Wednesday 29 April 2015 20:00:18 Pali Rohár wrote:
> > > > On Wednesday 29 April 2015 19:54:43 Gabriele Mazzotta
> > > > wrote:
> > > > > On Wednesday 29 April 2015 18:28:40 Pali Rohár wrote:
> > > > > > On Wednesday 29 April 2015 15:57:58 Gabriele Mazzotta
> > > > > > wrote:
> > > > > > > On Wednesday 29 April 2015 15:08:40 Pali Rohár
> > > > > > > wrote:
> > > > > > > > On Wednesday 29 April 2015 12:30:32 Gabriele
> > > > > > > > Mazzotta wrote:
> > > > > > > > > On Wednesday 29 April 2015 11:51:04 Pali Rohár
> > > > > > > > > wrote:
> > > > > > > > > > This is an ACPI driver for Dell laptops
> > > > > > > > > > which receive HW switch events. It exports
> > > > > > > > > > rfkill device dell-rbtn which provide
> > > > > > > > > > correct hard rfkill state.
> > > > > > > > > > 
> > > > > > > > > > Alex Hung added code for supporting Dell
> > > > > > > > > > laptops which have toggle button instead HW
> > > > > > > > > > slider switch. On these laptops toggle
> > > > > > > > > > button event is reported by new input
> > > > > > > > > > device (instead rfkill) as they do not have
> > > > > > > > > > hw radio switch.
> > > > > > > > > > 
> > > > > > > > > > It looks like those are two different
> > > > > > > > > > functions (rfkill, input device), but Dell
> > > > > > > > > > BIOS exports them via same ACPI device and
> > > > > > > > > > uses same ACPI functions. So code is in one
> > > > > > > > > > kernel driver.
> > > > > > > > > 
> > > > > > > > > I made a patch some time ago that I've just
> > > > > > > > > adapted. It allows to prefer RBTN_SLIDER over
> > > > > > > > > RBTN_TOGGLE. The main reason why I'd like to
> > > > > > > > > have the hardware switch is that the BIOS
> > > > > > > > > doesn't alter the soft state of the devices.
> > > > > > > > > This comes in handy when the function key
> > > > > > > > > controls multiple radio devices.
> > > > > > > > 
> > > > > > > > Now I'm thinking... is't this bug in wifi kernel
> > > > > > > > driver (which exports phy rfkill)? Or problem
> > > > > > > > somewhere else (userspace or kernel)?
> > > > > > > 
> > > > > > > What is the presumed bug you are referring to? The
> > > > > > > fact that the soft state doesn't change?
> > > > > > 
> > > > > > Can you remind me whats the problem on your laptop?
> > > > > 
> > > > > CRBT returns 0 (so RBTN_TOGGLE), but by default my
> > > > > laptop acts as if it returned 2 or 3, so we have to
> > > > > call ARBT.
> > > > > 
> > > > > As said before, there's no way to know when a platform
> > > > > whose CRBT method returns 0 or 1 also has the
> > > > > hardware switch, so to be sure that all the platforms
> > > > > have working function keys, some of them (such as
> > > > > mine) have to give up on the hardware switch.
> > > > 
> > > > Ok, and what happens when you load this v2 version? What
> > > > stopped working on your laptop?
> > > > 
> > > > Alex, can you help? Code for toggle laptop version is
> > > > originally yours.
> > > 
> > > When I press the Fn key, a _Qxx EC method is executed. The
> > > code path of this method depends on a variable set by
> > > ARBT.
> > > 
> > > When you call ARBT with 1 as argument, the variable is set
> > > to 1 and the _Qxx method does nothing but sending a
> > > notification (0x80) to RBTN whenever the function key is
> > > pressed.
> > > 
> > > When you call ARBT with 0 as argument, the variable is set
> > > to 0 and the _Qxx method both sends 0x80 to RBTN _and_
> > > toggle the state of the radio devices whenever the
> > > function key is pressed.
> > > 
> > > So in the end nothing _really_ breaks.
> > 
> > So in linux kernel is missing code for toggling state of
> > radio devices? And you can do that only by ACPI when ARBT
> > is called with 0, right?
> 
> Yes.
> 
> With Alex's code the kernel sends keypresses to userspace and
> userspace takes care of toggling the state of radio devices.

Alex, can you ask Dell for documentation how to enable/disable 
radio devices? Because when ARBT is set to 1, then system must 
take care of it but, linux does not support it yet...

-- 
Pali Rohár
pali.rohar@...il.com

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