於 一，2013-04-22 於 18:08 +0800，Aaron Lu 提到： > On 04/22/2013 10:18 AM, joeyli wrote: > > 於 五，2013-04-19 於 11:15 +0800，Aaron Lu 提到： > >> 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 > >> > >> -Aaron > >> > > > > Per WDDM document, OEM/ODM should keep the ACPI methods (_BQL, _BCM, > > _BQC) available for compliant to the OS that doesn't support WDDM, e.g. > > XP, Vista. > > Thanks for the information, so this suggests that acpi interface is > mostly used for pre-win8 OSes?(does win7 support WDDM?) Yes, they applied WDDM driver support on Windows 7 platform, but I don't know how many models only work on WDDM and have broken ACPI implementation. > > One interesting thing is, if they do not support acpi interface, why > they even bother to expose this interface in acpi table? > > -Aaron > I don't know, maybe they just thought that doesn't hurt anything because they only test Windows 7 or Windows 8, dependent on which OS preloaded and shipped with the machine. Use OSI string fallback to Windows XP or Vista mode sometimes can workaround problem when we are lucky. But, bad thing is OEM/ODM also didn't test XP/Vista code path with other ACPI features, e.g. S3/S4. Fallback to vendor mode, leave video driver to control backlight is what we done in platform driver, that's why we have quirk table. That best situation is we find a general logic to detect does issue machine shipped with WDDM driver. It's out of my knowledge. Thanks a lot! Joey Lee -- 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
