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

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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.

-Aaron

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