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 -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
