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

[Aaron Lu <aaron.lu@intel.com>]

On 04/21/2013 07:07 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.

The reason I mentioned this document is: we have been wondering how
windows handle such systems, and according to Ben's own use of win8, he
thinks win8 is not using acpi interface to control backlight. And the
words from the document that I pasted here kind of confirms this I think,
so I mentioned this document here, it is used to confirm how windows
handle such systems: using a native driver instead of acpi video
interface.

Thanks,
Aaron