From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Bertrik Sikken" Subject: Re: [REGRESSION BISECTED] backlight control stops workin with 3.14 and later Date: Fri, 22 Aug 2014 12:52:45 +0200 Message-ID: <687157eaa790afcc531adb1dfd2cd2dc.squirrel@webmail1.one.com> References: <53CE07D9.3090308@redhat.com> <53CF7651.4080305@redhat.com> <87d2c4qzdf.fsf@intel.com> <53ED11DD.3040104@sikken.nl> <878umpq36f.fsf@intel.com> <53F06B65.4090001@sikken.nl> <87wqa6nt91.fsf@intel.com> <7955720e6579951f4da64388ab4e1673.squirrel@webmail1.one.com> <87iolohakj.fsf@intel.com> <53F66849.4010608@sikken.nl> <87d2btm347.fsf@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from webmail1.one.com (squirrelmail.public.one.com [195.47.247.29]) by gabe.freedesktop.org (Postfix) with ESMTP id 472A26E889 for ; Fri, 22 Aug 2014 03:52:46 -0700 (PDT) In-Reply-To: <87d2btm347.fsf@intel.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" To: Jani Nikula Cc: "intel-gfx@lists.freedesktop.org hdegoede@redhat.com" , Bertrik Sikken List-Id: intel-gfx@lists.freedesktop.org > On Fri, 22 Aug 2014, Bertrik Sikken wrote: >> On 19-8-2014 3:29, Jani Nikula wrote: >>> On Tue, 19 Aug 2014, Bertrik Sikken wrote: >>>>> On Sun, 17 Aug 2014, Bertrik Sikken wrote: >>>>>> On 15-8-2014 3:43, Jani Nikula wrote: >>>>>>> On Thu, 14 Aug 2014, Bertrik Sikken wrote: >>>>>> >>>>>>>> Attached is dmesg output from booting kernel 3.14-2 (debian >>>>>>>> unstable) >>>>>>>> with drm.debug=0xe and the samsung_laptop module enabled, from my >>>>>>>> Samsung N150plus netbook. >>>>>>> >>>>>>> Have you tried 3.15? >>>>>> >>>>>> I've built the v3.15 kernel (using the .config file from debian >>>>>> unstable and doing make oldconfig). >>>>>> >>>>>> The backlight is at maximum brightness after boot and I can't >>>>>> control >>>>>> it using the backlight buttons, nor by writing to >>>>>> /sys/class/backlight/samsung/brightness >>>>>> (say half the value or 1/10th of max_brightness) >>>>>> >>>>>> Backlight does work when writing >>>>>> /sys/class/backlight/intel_backlight/brightness >>>>> >>>>> How about disabling samsung backlight module with 3.15? >>>> >>>> I'm not sure what you mean by that. >>>> >>>> As I understand it, there are three ways to control the backlight on >>>> this >>>> netbook: using intel_backlight, samsung_laptop (using a "sabi" >>>> interface) >>>> and acpi_video. >>>> Backlight control using the samsung_laptop driver no longer seems to >>>> work >>>> after the change. If I disable it (e.g. by blacklisting it), I expect >>>> it >>>> to no longer work at all obviously. >>>> >>>> What do you want me to test exactly? >>> >>> If the intel_backlight interface works in 3.15, I presume the problem >>> is >>> that you have a non-functional samsung backlight interface that is >>> preferred over intel_backlight by your userspace. >> >> I tested the intel_backlight interface in linux v3.15 with the samsung >> backlight module blacklisted. The intel_backlight interface still works. > > I read that as, "I no longer have problems with backlight". The problem as I see it, is that the bisected backlight change in the intel-gfx driver caused the samsung_laptop backlight mechanism to break, while they apparently were able to play nice with each other before. You could consider having two drivers trying to access the same hardware as a more general linux kernel bug. As I understand it now, the intel-gfx driver talks directly to the hardware and the samsung_laptop driver talks through a BIOS interface (SABI = "Samsung advanced BIOS interface"). I'm not trying to put the blame on any of the two drivers, just looking for the best solution to a practical problem. With kind regards, Bertrik Sikken