From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Subject: Re: [Regression]: Changing brightness does not work with v3.16-rc4
Date: Mon, 14 Jul 2014 21:10:47 +0200
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References: <20140712180636.698e2e4c@saldaea> <20140714203422.171a3e58@saldaea> <1853509.BZhYt7FKHM@vostro.rjw.lan>
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To: Julian Wollrath <jwollrath@web.de>
Cc: linux-acpi@vger.kernel.org, Aaron Lu <aaron.lu@intel.com>

On Monday, July 14, 2014 09:02:34 PM Rafael J. Wysocki wrote:
> On Monday, July 14, 2014 08:34:22 PM Julian Wollrath wrote:
> > Am Mon, 14 Jul 2014 20:21:19 +0200
> > schrieb "Rafael J. Wysocki" <rjw@rjwysocki.net>:
> > 
> > > On Saturday, July 12, 2014 06:24:52 PM Julian Wollrath wrote:
> > > > Hi,
> > > > 
> > > > > changing the brightness on my Thinkpad X230 with Intel HD4000
> > > > > graphics, stopped working after commit 886129a8eebe (ACPI / video:
> > > > > change acpi-video brightness_switch_enabled default to 0).
> > > > > Changing it back to 1, fixes the problem, if "acpi_osi=!Windows
> > > > > 2012" is also set. Before that commit just setting
> > > > > "acpi_osi=!Windows 2012" was enough to get changing the
> > > > > brightness working.
> > > >
> > > > small correction: It setting "acpi_osi=!Windows 2012" does only help
> > > > when using a kernel with commit 886129a8eebe as HEAD, with v3.16-rc4
> > > > setting video.brightness_switch_enabled=1 and acpi_osi=!Windows
> > > > 2012 or just one of them, does not make changing the brightness
> > > > work again.
> > > 
> > > And reverting commit 751109aad583 (ACPI / video: Change the default
> > > for video.use_native_backlight to 1) make that last problem go away,
> > > right?
> > > 
> > > We are going to rever commit 886129a8eebe for other reasons, so can
> > > you please revert it from 3.16-rc5 on your system and report back?
> > Yes, with both 751109aad583 and 886129a8eebe reverted, changing the
> > brightness works again.
> 
> What if you revert 886129a8eebe alone?

I mean, what exactly do you need to pass to the kernel command line in that
case to make brightness switching work?

Rafael