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: Sun, 21 Apr 2013 19:07:04 +0800 Message-ID: <5173C858.10208@intel.com> References: <1360599681-24781-1-git-send-email-seth.forshee@canonical.com> <515BD48B.7000901@bjencks.net> <5170B6ED.2040408@intel.com> <1595406.DWIUmGvNI0@vostro.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-da0-f53.google.com ([209.85.210.53]:39683 "EHLO mail-da0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751012Ab3DULH0 (ORCPT ); Sun, 21 Apr 2013 07:07:26 -0400 Received: by mail-da0-f53.google.com with SMTP id n34so126628dal.12 for ; Sun, 21 Apr 2013 04:07:26 -0700 (PDT) In-Reply-To: <1595406.DWIUmGvNI0@vostro.rjw.lan> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: "Rafael J. Wysocki" Cc: Ben Jencks , Seth Forshee , Len Brown , linux-acpi@vger.kernel.org, joeyli , Matthew Garrett 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. -Aaron