From mboxrd@z Thu Jan 1 00:00:00 1970 From: Aaron Lu Subject: Re: [PATCH] ACPI: Disable Windows 8 compatibility for some Lenovo ThinkPads Date: Fri, 19 Apr 2013 11:15:57 +0800 Message-ID: <5170B6ED.2040408@intel.com> References: <1360599681-24781-1-git-send-email-seth.forshee@canonical.com> <5158E8A0.3050904@intel.com> <20130401130340.GA3269@thinkpad-t410> <515AA007.1050305@intel.com> <20130402130000.GA12381@thinkpad-t410> <515BD48B.7000901@bjencks.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from mga09.intel.com ([134.134.136.24]:21629 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S967861Ab3DSDOa (ORCPT ); Thu, 18 Apr 2013 23:14:30 -0400 In-Reply-To: <515BD48B.7000901@bjencks.net> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Ben Jencks Cc: Seth Forshee , Aaron Lu , Len Brown , "Rafael J. Wysocki" , linux-acpi@vger.kernel.org, joeyli , Matthew Garrett 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