From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Jencks Subject: Re: [PATCH] ACPI: Disable Windows 8 compatibility for some Lenovo ThinkPads Date: Wed, 13 Feb 2013 16:09:52 -0500 Message-ID: <511C0120.80707@bjencks.net> References: <1360599681-24781-1-git-send-email-seth.forshee@canonical.com> <20130211175213.GA25139@srcf.ucam.org> <20130211190617.GH13768@thinkpad-t410> <20130211190914.GA27364@srcf.ucam.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: Received: from mail-vc0-f173.google.com ([209.85.220.173]:45604 "EHLO mail-vc0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752010Ab3BMVJz (ORCPT ); Wed, 13 Feb 2013 16:09:55 -0500 Received: by mail-vc0-f173.google.com with SMTP id fy7so1060786vcb.4 for ; Wed, 13 Feb 2013 13:09:55 -0800 (PST) In-Reply-To: <20130211190914.GA27364@srcf.ucam.org> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Matthew Garrett Cc: Seth Forshee , Len Brown , "Rafael J. Wysocki" , linux-acpi@vger.kernel.org, joeyli On 02/11/2013 02:09 PM, Matthew Garrett wrote: > On Mon, Feb 11, 2013 at 01:06:17PM -0600, Seth Forshee wrote: >> On Mon, Feb 11, 2013 at 05:52:13PM +0000, Matthew Garrett wrote: >>> 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. > > Right. My concern here is that Windows clearly doesn't trigger the > issue, and so there's some chance that we'll see similar issues on other > machines. Disabling Windows 8 compatibility isn't really an option. One > choice might be to have the ACPI video driver set all intermediate > values if the system makes the Windows 8 OSI call? Stupid hack idea: what about trying all the levels _BCL reports and seeing which ones change _BQC? Then filter out any that don't really exist. It might make bootup look odd, seeing the backlight quickly scan through all brightness levels, but it's only once per boot. -Ben