Re: [Regression]: Changing brightness does not work with v3.16-rc4

[Julian Wollrath <jwollrath@web.de>]

Am Wed, 16 Jul 2014 10:36:56 +0800
schrieb Aaron Lu <aaron.lu@intel.com>:

> On 07/15/2014 02:56 AM, Julian Wollrath wrote:
> > Am Mon, 14 Jul 2014 21:10:47 +0200
> > schrieb "Rafael J. Wysocki" <rjw@rjwysocki.net>:
> > 
> >> 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?
> > I need to pass
> >   acpi_osi="!Windows 2012" video.brightness_switch_enabled=1
> > video.use_native_backlight=-1
> > 
> > If I leave one of these parameters out, the brightness switch stops
> > working.
> 
> If you only pass the following 2 cmdline options:
> acpi_osi="!Windows 2012" video.brightness_switch_enabled=1
> Will there be the /sys/class/backlight/acpi_videoX file?

Yes, and interestingly with v3.16-rc5 the brightness switching works
with just these two options.

Cheers,
Julian