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: Tue, 02 Apr 2013 17:08:23 +0800 Message-ID: <515AA007.1050305@intel.com> References: <1360599681-24781-1-git-send-email-seth.forshee@canonical.com> <5158E8A0.3050904@intel.com> <20130401130340.GA3269@thinkpad-t410> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from mga03.intel.com ([143.182.124.21]:46345 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753812Ab3DBJHL (ORCPT ); Tue, 2 Apr 2013 05:07:11 -0400 In-Reply-To: <20130401130340.GA3269@thinkpad-t410> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Seth Forshee Cc: Len Brown , "Rafael J. Wysocki" , linux-acpi@vger.kernel.org, Ben Jencks , joeyli , Matthew Garrett On 04/01/2013 09:03 PM, Seth Forshee wrote: > 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. OK, and if GUI tool like g-s-d decides to go some more steps when adjusting backlight level, it may always choose the non-functional values. Hmm, doesn't seem to be an usable way then. I really wondered, how Windows handled this, it should have the same problem, unless they are not using the acpi video interface? > > 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. Suppose we are at level 100, and the user sets the target level to be 20, then we will need to call _BCM 80 times? Thanks, Aaron