[Intel-gfx] Bad flicker on skylake HQD due to code in the 4.7 merge window

[James Bottomley]

On Fri, 2016-07-08 at 13:19 +0300, Ville Syrjälä wrote:
> On Thu, Jul 07, 2016 at 12:19:36PM -0700, James Bottomley wrote:
> > 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 at HansenPartnership.com> wrote:
> > > > > > > > OK, my candidate bad commit is this one:
> > > > > > > > 
> > > > > > > > commit a05628195a0d9f3173dd9aa76f482aef692e46ee
> > > > > > > > Author: Ville Syrjälä <ville.syrjala at 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.
> 
> Oh well, I suspected as much. Which BIOS version did you have 
> exactly?

As mentioned upthread, now 1.4.3 since skylake microcode was
potentially implicated in the problem:

http://mid.gmane.org/1466179729.2271.33.camel@HansenPartnership.com

> If I'm reading the Dell website correctly there's a new one (1.4.4)
> released on Jun 30, which is after you reported the issue. Might be
> I'm reading the wrong thing though. Can you double check this?

New bios doesn't change the microcode:

[    2.390172] microcode: CPU0 sig=0x406e3, pf=0x80, revision=0x8a

And the flicker is still present.

James