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 at ffwll.ch Mobile: +41 (0)79 365 57 48
