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SubjectRe: [Intel-gfx] Bad flicker on skylake HQD due to code in the 4.7 merge window
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On Thu, 2016-07-07 at 09:55 -0700, James Bottomley wrote:
> On Thu, 2016-07-07 at 19:14 +0300, Ville Syrjälä wrote:
> > On Tue, Jun 21, 2016 at 06:44:34PM +0300, Ville Syrjälä wrote:
> > > On Tue, Jun 21, 2016 at 09:53:15AM -0400, James Bottomley wrote:
> > > > On Mon, 2016-06-20 at 11:03 +0300, Jani Nikula wrote:
> > > > > Cc: Ville
> > > > >
> > > > > On Mon, 20 Jun 2016, James Bottomley <
> > > > > James.Bottomley@HansenPartnership.com> wrote:
> > > > > > OK, my candidate bad commit is this one:
> > > > > >
> > > > > > commit a05628195a0d9f3173dd9aa76f482aef692e46ee
> > > > > > Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > > > > Date: Mon Apr 11 10:23:51 2016 +0300
> > > > > >
> > > > > > drm/i915: Get panel_type from OpRegion panel details
> > > > > >
> > > > > > After being more careful about waiting to identify flicker,
> > > > > > this one seems to be the one the bisect finds. I'm now
> > > > > > running v4.7-rc3 with this one reverted and am currently
> > > > > > seeing no flicker problems. It is, however, early days
> > > > > > because the flicker can hide for long periods, so I 'll
> > > > > > wait
> > > > > > until Monday evening and a few reboots before declaring
> > > > > > victory.
> > > > >
> > > > > If that turns out to be the bad commit, it doesn't really
> > > > > surprise me, and that in itself is depressing.
> > > >
> > > > As far as I can tell, after running for a day with this
> > > > reverted,
> > > > this is the problem. The flicker hasn't appeared with it
> > > > reverted. It's pretty noticeable with this commit included.
> > >
> > > Hmm. The only difference I can see is low vs. normal vswing.
> > > Panel
> > > 0 has low, panel 2 has normal. So either the VBT or opregion is
> > > telling utter lies, or there's some other bug in our low vswing
> > > support.
> >
> > I did a quick once over of out DDI vswing stuff and didn't find
> > anything too serious. There were some buglets in the iboost
> > handling,
> > but I'm not very hopeful that fixing those would help with your
> > machine.
> >
> > Here's a branch anyway in case you want to give it a go:
> > git://github.com/vsyrjala/linux.git ddi_iboost_fixes
> >
> > Actually, I think the only patch in there that might make a
> > difference is 15d887855180 ("drm/i915: Fix iboost setting for DDI
> > with 4 lanes on SKL")
>
> Running with it now (the entire branch). So far it looks OK, but
> I'll give it a couple of days to see if anything manifests before
> declaring victory.

Bad news, I'm afraid: after a couple of hours of run time, there is now
noticeable flicker on the display, so although the iboost fixes may
have lessened it, it's still present.

James


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