Re: [PATCH] ACPI: Disable Windows 8 compatibility for some Lenovo ThinkPads

[Seth Forshee <seth.forshee@canonical.com>]

On Mon, Apr 22, 2013 at 08:11:17PM +0800, Aaron Lu wrote:
> On 04/22/2013 07:51 PM, Rafael J. Wysocki wrote:
> > On Monday, April 22, 2013 05:39:43 PM Aaron Lu wrote:
> >> On 04/22/2013 05:42 AM, Rafael J. Wysocki wrote:
> >>> On Sunday, April 21, 2013 07:07:04 PM Aaron Lu wrote:
> >>>> On 04/21/2013 06:06 AM, Rafael J. Wysocki wrote:
> >>>>> On Friday, April 19, 2013 11:15:57 AM Aaron Lu wrote:
> >>>>>> On 04/03/2013 03:04 PM, Ben Jencks wrote:
> >>>>>>> On 04/02/2013 09:00 AM, Seth Forshee wrote:
> >>>>>>>> On Tue, Apr 02, 2013 at 05:08:23PM +0800, Aaron Lu wrote:
> >>>>>>>>>
> >>>>>>>>> I really wondered, how Windows handled this, it should have the same
> >>>>>>>>> problem, unless they are not using the acpi video interface?
> >>>>>>>>
> >>>>>>>> I can only guess.
> >>>>>>>>
> >>>>>>>> I think I remember reading that Windows 8 does smooth backlight
> >>>>>>>> transitions, so it may well hit every intermediate brightness value.
> >>>>>>>> Lenovo could also be supplying a driver which rounds values to the
> >>>>>>>> nearest working value or uses some other interface or something else.
> >>>>>>>
> >>>>>>> Just checked; Windows 8 doesn't use the ACPI interface. It seems to have
> >>>>>>> access to at least 100 distinct brightness levels.
> >>>>>>
> >>>>>> I just came across a document on win8 backlight control, it has words
> >>>>>> like this:
> >>>>>> "
> >>>>>> In Windows 8, the primary mechanism by which a platform should expose
> >>>>>> its display brightness control functionality is the Windows Display
> >>>>>> Driver Model (WDDM) miniport Device Driver Interfaces (DDI).
> >>>>>> "
> >>>>>> So looks like, on win8, ACPI interface is not used for these systems.
> >>>>>>
> >>>>>> The link for the document is here:
> >>>>>> http://msdn.microsoft.com/en-US/library/windows/hardware/jj159305
> >>>>>
> >>>>> OK, so what does that mean for the issue at hand?
> >>>>
> >>>> That means, we should not try to use acpi video interface to control
> >>>> backlight on these systems if they are in win8 mode.
> >>>
> >>> In that case, how are we going to indentify "these systems"?
> >>
> >> Sorry, I don't know.
> >>
> >> According to the following bug page:
> >> https://bugzilla.kernel.org/show_bug.cgi?id=51231
> >> "these systems" now include: thinkpad x230, t430s, t530, L430.

Also W530, X1 Carbon, and Edge E330.

> > I suppose we need to blacklist them to start with.  I wouldn't like to apply
> > any general changes before we know how many different systems are affected by
> > this particular issue.
> 
> I totally agree.

Are you sure that all of these machines have an alternate interface for
userspace to change the brightness? I know that I've got a non-Lenovo
machine with nVidia graphics for which nouveau exposes no backlight
control, and I have no idea what controls are exposed by the proprietary
graphics drivers.

Seth