From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Vetter Subject: Re: [PATCH 2/2] drm/i915: quirk disable i915 backlight on Dell XPS 13z Date: Fri, 27 Apr 2012 23:25:12 +0200 Message-ID: <20120427212512.GL5147@phenom.ffwll.local> References: <1335374922-7905-1-git-send-email-kamal@canonical.com> <1335374922-7905-2-git-send-email-kamal@canonical.com> <1335560169.3877.99.camel@fourier> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-we0-f177.google.com (mail-we0-f177.google.com [74.125.82.177]) by gabe.freedesktop.org (Postfix) with ESMTP id 5CC059E7C2 for ; Fri, 27 Apr 2012 14:24:13 -0700 (PDT) Received: by werp11 with SMTP id p11so899210wer.36 for ; Fri, 27 Apr 2012 14:24:12 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1335560169.3877.99.camel@fourier> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org Errors-To: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org To: Kamal Mostafa Cc: Robert Hooker , Intel Graphics Development List-Id: intel-gfx@lists.freedesktop.org On Fri, Apr 27, 2012 at 01:56:09PM -0700, Kamal Mostafa wrote: > On Thu, 2012-04-26 at 22:07 +0200, Daniel Vetter wrote: > > ... > > To cut things short: This time around I want more justification for the > > quirk than just "this makes this one machine work somehow". > > > A bit more detail... > > On this Dell XPS 13z "Ultrabook" (sandybridge_m 0x0116) when > intel_backlight/brightness gets stuffed with any value except 0 or > max_brightness, the backlight cycles between flashing (like a strobe > light!) and then pulsating (bright to dim to bright). That > flashing/pulsating cycle repeats continuously, about every 2 seconds. > The behavior is affected by the value stuffed into brightness more or > less along the lines of: > > 0: very dim, totally stable > 1: flashes like crazy for about 1.5 sec, then pulsates for 0.5 sec > 1000: flashes for about 0.5 sec, then pulsates for about 1.5 sec > 2000: flashes very briefly, then pulsates for about 2 sec > 3000: flickers, then pulsates for about 2 sec > 4000 pulsates continuously, every 2 sec > 4882: (max_brightness) full brightness, stable > > This behavior manifests both in X and in a text VT, and occurs with or > without the presence of other backlight interfaces besides > intel_backlight. It does not appear to me to be a userspace problem. > > The additional wrinkle is that this machine presents an acpi_video0 > backlight interface as well, and it even works properly -- but *only* > after you specifically stuff 0 into intel_backlight/brightness (or if > intel_backlight is disabled by the proposed quirk). > > Any non-zero intel_backlight/brightness value prevents acpi_video0 from > working. When intel_backlight is set to max_brightness (like at boot), > acpi_video0/brightness seems to have no effect at all; when > intel_backlight is set to other non-zero values, the flashing/pulsating > behavior occurs. > > I'd be (quite) happy to test a proper intel_backlight fix, but in the > meantime disabling it by quirk seems appropriate for this machine, since > that allows the acpi_video0 interface to work out of the box. > > Thanks for considering it, Hm. Can you please install intel-gpu-tools and attach the output of intel_reg_dumper? I have an idea ... Thanks, Daniel -- Daniel Vetter Mail: daniel@ffwll.ch Mobile: +41 (0)79 365 57 48