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. 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. Thanks, Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- 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
