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, 11 Feb 2013 13:06:17 -0600 Message-ID: <20130211190617.GH13768@thinkpad-t410> References: <1360599681-24781-1-git-send-email-seth.forshee@canonical.com> <20130211175213.GA25139@srcf.ucam.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from youngberry.canonical.com ([91.189.89.112]:45898 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758329Ab3BKTGX (ORCPT ); Mon, 11 Feb 2013 14:06:23 -0500 Content-Disposition: inline In-Reply-To: <20130211175213.GA25139@srcf.ucam.org> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Matthew Garrett Cc: Len Brown , "Rafael J. Wysocki" , linux-acpi@vger.kernel.org, Ben Jencks , joeyli On Mon, Feb 11, 2013 at 05:52:13PM +0000, Matthew Garrett wrote: > On Mon, Feb 11, 2013 at 10:21:21AM -0600, 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. > > So the problem is that userspace is writing values that don't happen to > be aligned with the values the hardware reacts to, and so nothing gets > changed? Yes. The values are valid according to to _BCL, but _BCM is discarding any values that aren't contained in an array named BRTW. BRTW is literally the object returned by _BCL returns for !Windows 2012. Here's a link to the AML if you'd like to take a look. http://people.canonical.com/~sforshee/x230-acpi-tables/SSDT1.dsl Seth