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: Sun, 11 Jan 2015 11:37:52 +0100 Message-ID: <54B25280.6010604@redhat.com> References: <1420444624-8313-1-git-send-email-hdegoede@redhat.com> <20150111061602.GA1677@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]:43812 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751267AbbAKKiD (ORCPT ); Sun, 11 Jan 2015 05:38:03 -0500 In-Reply-To: <20150111061602.GA1677@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 11-01-15 07:16, Matthew Garrett wrote: > On Mon, Jan 05, 2015 at 08:57:04AM +0100, Hans de Goede wrote: >> The L521X variant of the Dell XPS15 has integrated nvidia graphics, and >> backlight control does not work properly when using the native interfaces. > > I'm not convinced that the assessment of this bug is correct. Is the > system using the nvidia graphics device? I do not know. > If so, why is userspace writing to the intel backlight device? 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. What this commit does is disable the disabling of acpi-video, and after that userspace will see an acpi_video0 backlight under /sys/class/backlight, use that and then things work, this has been confirmed by the bug reporter. 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. Regards, Hans