The quirk was added as what I'd say was a stopgap measure in
commit e85843bec6
Author: Kamal Mostafa <kamal@canonical.com>
Date: Fri Jul 19 15:02:01 2013 -0700
drm/i915: quirk no PCH_PWM_ENABLE for Dell XPS13 backlight
without really digging into what was going on.
Also, as mentioned in the related bug [1], having the quirk regressed
some of the machines it was supposed to fix to begin with, and there
were patches posted to disable the quirk on such machines [2]!
The fact is, we do need the BLM_PCH_PWM_ENABLE bit set to have
backlight. With the quirk, we've relied on BIOS to have set it, and our
save/restore code to retain it. With the full backlight setup at enable,
we have no place for things that rely on previous state.
With the per platform hooks, we've also made a change in the PCH
platform enable order: setting the backlight duty cycle between CPU and
PCH PWM enable. Some experimenting and
commit 770c12312a
Author: Takashi Iwai <tiwai@suse.de>
Date: Sat Aug 11 08:56:42 2012 +0200
drm/i915: Fix blank panel at reopening lid
indicate that we can't set the backlight before enabling CPU PWM; the
value just won't stick. But AFAICT we should do it before enabling the
PCH PWM.
Finally, any fallout we should fix properly, preferrably without quirks,
and absolutely without quirks that rely on existing state. With the per
platform hooks have much more flexibility to adjust the sequence as
required by platforms.
[1] https://bugzilla.kernel.org/show_bug.cgi?id=47941
[2] http://lkml.kernel.org/r/1378229848-29113-1-git-send-email-kamal@canonical.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
bc0bb9fd1c