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

[James Bottomley]

On Fri, 2016-06-17 at 16:06 -0700, James Bottomley wrote:
> On Fri, 2016-06-17 at 16:34 +0300, Jani Nikula wrote:
> > On Fri, 17 Jun 2016, Daniel Vetter <daniel at ffwll.ch> wrote:
> > > On Thu, Jun 16, 2016 at 03:42:12PM -0700, James Bottomley wrote:
> > > > On Thu, 2016-06-16 at 14:29 -0700, James Bottomley wrote:
> > > > > On Thu, 2016-06-16 at 23:24 +0200, Daniel Vetter wrote:
> > > > > > I guess we'll need the bisect on this one to make progress.
> > > > > 
> > > > > Sigh, I was afraid that might be the next step.
> > > > 
> > > > OK, I have a curious data point.  I assumed the problem would
> > > > be
> > > > somewhere in the drm update, so I started bisecting that at the
> > > > top. 
> > > >  However, the top most commit:
> > > > 
> > > > commit 1d6da87a3241deb13d073c4125d19ed0e5a0c62c
> > > > Merge: 1f40c49 a39ed68
> > > > Author: Linus Torvalds <torvalds at linux-foundation.org>
> > > > Date:   Mon May 23 11:48:48 2016 -0700
> > > > 
> > > >     Merge branch 'drm-next' of
> > > > git://people.freedesktop.org/~airlied/linux
> > > > 
> > > > Isn't actually bad.  There's no flicker here, so whatever
> > > > caused
> > > > the
> > > > problem came from some update after this.
> > > 
> > > There was a fixes pull after this. Might be worth it to restrict
> > > to
> > > just
> > > the i915 changes, which are just
> > > 5b4fd5b1111b1230cd037..157d2c7fad0863222
> > > 
> > > Looking at those nothing seems to stick out which might explain
> > > what's
> > > happening for you.
> 
> OK, so just on the firmware, the system seems less flickery with the
> new 1.4.3 UEFI, so I'm starting to think it is a Skylake errata 
> issue.  The flicker isn't gone for good, but seems to be reboot 
> dependent (it's there in some boots, but gone on a reboot).
> 
> > This should be easy enough to try before bisecting:
> > http://patchwork.freedesktop.org/patch/msgid/1466162081-12042-1-git
> > -s
> > end-email-mika.kahola at intel.com
> 
> Applying this didn't seem to make a difference: still there on some 
> and gone on other reboots.

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.

James