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

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

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