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

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Date:	Tue, 5 May 2015 22:55:46 -0700
From:	Darren Hart <dvhart@...radead.org>
To:	Gabriele Mazzotta <gabriele.mzt@...il.com>
Cc:	Pali Rohár <pali.rohar@...il.com>,
	Alex Hung <alex.hung@...onical.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	"platform-driver-x86@...r.kernel.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 Tue, May 05, 2015 at 11:23:05PM +0200, Gabriele Mazzotta wrote:
> On Thursday 30 April 2015 09:44:29 Pali Rohár wrote:
> > On Thursday 30 April 2015 14:06:27 Alex Hung wrote:
> > > Method ABRT is to be used by driver to disable BIOS handling of radio
> > > button. So the changes in behaviours observed by Gabriele is expected.
> > > I have seen other systems behave the same way.
> > > 
> > 
> > Right, that after that ARBT call operating system get full control over
> > radio devices and ACPI/BIOS will not automatically enable/disable them.
> > I think this is OK.
> > 
> > But for that we need also support for manually enable/disable radio
> > devices and code for this support is missing. Or do DELLABCE/RBTN acpi
> > devices somehow support enabling/disabling it via system/kernel request?
> > 
> > > I do also see firmware only sends Notify(RBTN, 0x80) and no hard block
> > > whether ABRT(1) is called or not.  Thus keycode are the only option on
> > > those machines.
> > > 
> > 
> > Key is ok, but we *must* have ability to hard block it via some
> > ACPI/WMI/BIOS/FW/etc... call. Otherwise ARBT(1) is no go as users should
> > be able to enable/disable their radio devices (bluetooth for powersave)
> 
> Does it really matter in the end? As I understand it, radio devices are
> off either way.

As a point of reference for consideration, we recently dropped the Thinkpad
hardware mute button because it seriously complicated everything in what appears
to be a similar sort of situation. By eliminating the hardware mute and relying
purely on software mute, we were able to provide a much more consistently
functional driver.

Also note that this driver provided a "software_mute" module parameter to allow
the user to control this.

I believe this provides some relevant precedent for your consideration. I don't
want to add parameters casually, but it could be one is warranted here.

-- 
Darren Hart
Intel Open Source Technology Center
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