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. > > 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. Thanks, Aaron -- 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
