From mboxrd@z Thu Jan 1 00:00:00 1970 From: Seth Forshee Subject: Re: [PATCH] ACPI: Disable Windows 8 compatibility for some Lenovo ThinkPads Date: Mon, 1 Apr 2013 08:03:40 -0500 Message-ID: <20130401130340.GA3269@thinkpad-t410> References: <1360599681-24781-1-git-send-email-seth.forshee@canonical.com> <5158E8A0.3050904@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from youngberry.canonical.com ([91.189.89.112]:49897 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756444Ab3DANDv (ORCPT ); Mon, 1 Apr 2013 09:03:51 -0400 Content-Disposition: inline In-Reply-To: <5158E8A0.3050904@intel.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Aaron Lu Cc: Len Brown , "Rafael J. Wysocki" , linux-acpi@vger.kernel.org, Ben Jencks , joeyli , Matthew Garrett On Mon, Apr 01, 2013 at 09:53:36AM +0800, Aaron Lu wrote: > On 02/12/2013 12:21 AM, Seth Forshee wrote: > > The AML implementation for brightness control on several ThinkPads > > contains a workaround to meet a Windows 8 requirement of 101 brightness > > levels [1]. The implementation is flawed, as only 16 of the brighness > > values reported by _BCL affect a change in brightness. _BCM silently > > discards the rest of the values. Disabling Windows 8 compatibility on > > these machines reverts them to the old behavior, making _BCL only report > > the 16 brightness levels which actually work. Add a quirk to do this > > along with a dmi callback to disable Win8 compatibility. > > If we disable the _BQC(i.e. set cap._BQC=0) for these systems, will the > problem go away? If so, I think perhaps we can put these systems into a > _BQC quirk table and set cap._BQC=0 for them. That helps a little, but we're still left with only 16 of the 101 brightness levels causing any change in brightness. The firmware isn't rounding the "bad" values or anything like that; it just silently ignores them. I submitted a second set of patches [1] which writes all intermediate values between the old and new brightness values and disables _BQC for these machines (empirically rather than using a quirk table), though no one seems to be interested in reviewing them. Seth [1] http://www.spinics.net/lists/linux-acpi/msg42525.html