From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hans de Goede Subject: RFC: changing acpi-video brightness_switch_enabled default to 0 Date: Fri, 02 May 2014 11:32:15 +0200 Message-ID: <5363661F.1050301@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from mx1.redhat.com ([209.132.183.28]:53988 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751364AbaEBJcZ (ORCPT ); Fri, 2 May 2014 05:32:25 -0400 Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Zhang Rui , "Rafael J. Wysocki" , Len Brown Cc: linux-acpi , Josh Boyer Hi All, I was already considering asking for $subject for a while, but I did not see any bug reports caused by it so I didn't ask. Until today I discovered that I'm not seeing any bugs because Fedora is carrying a kernel patch changing the default. A quick google search for brightness_switch_enabled OTOH reveals that for other distros it is a serious problem, see ie: https://bugs.launchpad.net/gnome-settings-daemon/+bug/527157 http://askubuntu.com/questions/173921/why-does-my-thinkpad-brightness-control-skip-steps The problem is that acpi-video is unique in that it not only generates brightness up/down keypresses, but also (sometimes) actively changes the brightness itself. This presents an inconsistent kernel interface to userspace, basically there are 2 different scenarios, depending on the laptop model: 1) On some laptops a brightness up/down keypress means: show a brightness osd with the current brightness, iow it is a brightness has changed notification. 2) Where as on (a lot of) other laptops it means a brightness up/down key was pressed, deal with it. Most of the desktop environments interpret any press as in scenario 2, and change the brightness up / down as a response to the key events, causing it to be changed twice, once by acpi-video and once by the DE. With the new default for video.use_native_backlight we will be moving even more laptops over to behaving as in scenario 2. Making the remaining laptops even more of a weird exception. Also note that it is hard to detect scenario 1 properly in userspace, and AFAIK none of the DE-s deasls with it. Therefor I would like to propose to change the brightness_switch_enabled default to 0. Regards, Hans