[Intel-gfx] Regression: Backlight not coming on after resume.

[James Courtier-Dutton]

On Feb 28, 2013 5:20 PM, "Takashi Iwai" <tiwai at suse.de> wrote:
>
> At Thu, 28 Feb 2013 17:33:56 +0200,
> Jani Nikula wrote:
> >
> > On Thu, 28 Feb 2013, James Courtier-Dutton <james.dutton at gmail.com>
wrote:
> > > Bisect done on tree:
> > > git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
> > > Worked on 3.7.
> > > Broken on 3.8
> > >
> > > Problem: "Backlight not coming on after resume."
> > > git finally bisected  for my Samsung Serial 7 Laptop.
> > > Bisecting: 0 revisions left to test after this (roughly 0 steps)
> > > [cf0a6584aa6d382f802f2c3cacac23ccbccde0cd] drm/i915: write backlight
> > > harder     <- This is the problem commit. Seems that fixing some
> > > machines breaks others, based on the existing comments on that patch.
> >
> > The backlight haunts us again. Could you post the dmesg with
> > drm.debug=0xe module parameter, first running vanilla 3.8, and then with
> > the bad commit reverted, please?
> >
> > Might not be a bad idea to file a bug on Product=DRI,
> > Component=DRM/Intel at https://bugs.freedesktop.org (see
> > https://01.org/linuxgraphics/documentation/how-report-bugs-0 for
> > details) and attach your bisect results and the dmesgs there.
>
> I'm afraid the patch doesn't do it right.  It fixes for Dell, but the
> old problem on others back by that.  It was merged before actually
> testing on the machines the original fix was intended for.
>
> Now I can confirm a problem (partially) with the latest Linus tree on
> a new laptop.  I write "partially" because it happens only during the
> splash screen of S4 hibernation, so I've ignored, so far.
>
> James, try to revert that commit.  Does it fix?
>
> If so, you should check the output of intel_reg_dumper at broken and
> working states.
>
Can someone point me to a datasheet that relates to this bit of code, so i
can understand what all the registers do.
I would like to understand the code in order to suggest a better fix.
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