From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: [PATCH] ACPI: Disable Windows 8 compatibility for some Lenovo ThinkPads Date: Sun, 21 Apr 2013 00:06:53 +0200 Message-ID: <1595406.DWIUmGvNI0@vostro.rjw.lan> References: <1360599681-24781-1-git-send-email-seth.forshee@canonical.com> <515BD48B.7000901@bjencks.net> <5170B6ED.2040408@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7Bit Return-path: Received: from hydra.sisk.pl ([212.160.235.94]:39218 "EHLO hydra.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755449Ab3DTV6v (ORCPT ); Sat, 20 Apr 2013 17:58:51 -0400 In-Reply-To: <5170B6ED.2040408@intel.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Aaron Lu Cc: Ben Jencks , Seth Forshee , Len Brown , linux-acpi@vger.kernel.org, joeyli , Matthew Garrett 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? Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.