From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hans de Goede Subject: Re: [PATCH] acpi-video: Add disable_native_backlight quirk for Dell XPS15 L521X Date: Mon, 12 Jan 2015 10:12:57 +0100 Message-ID: <54B39019.2070501@redhat.com> References: <1420444624-8313-1-git-send-email-hdegoede@redhat.com> <20150111061602.GA1677@srcf.ucam.org> <54B25280.6010604@redhat.com> <20150112024411.GA6831@srcf.ucam.org> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mx1.redhat.com ([209.132.183.28]:57534 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751859AbbALJNF (ORCPT ); Mon, 12 Jan 2015 04:13:05 -0500 In-Reply-To: <20150112024411.GA6831@srcf.ucam.org> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Matthew Garrett Cc: "Rafael J. Wysocki" , linux-acpi@vger.kernel.org Hi, On 12-01-15 03:44, Matthew Garrett wrote: > On Sun, Jan 11, 2015 at 11:37:52AM +0100, Hans de Goede wrote: > >> Userspace is writing to the intel_backlight device because it is the >> only one present under /sys/class/backlight, as we disable acpi-video >> on win8 ready laptops by default now. > > Why is nouveau not providing a backlight device? I do not know. >> The commit message may not be 100% accurate, although I believe this is >> related to the laptop having nvidia graphics, but the code / fix is correct >> regardless. > > I don't think we have enough evidence to know whether this fix is > correct. This fix fixes a regression introduced from kernel 3.15 to 3.16, when we switched video.use_native_brightness's default from 0 to 1, all this patch does is restore the previous behaviour on this specific model as the new behaviour is broken. So this is in essence a model targeted "revert" fixing a regression and as such most certainly is correct, given the clear no regressions policy the kernel has. Might it be good to dive deeper as to why the intel_backlight interface does not work, yes certainly. Regards, Hans